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Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #756574
11/19/18 6:09 pm
11/19/18 6:09 pm
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Magnetoman Online content OP

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Originally Posted by AML
I've been looking forward to the revival of this thread!
Because of other obligations I won't be able to do any more work on the Spitfire for a week, but this is an actual revival, not a post about hoped-for work that might or might not happen. As a result of rebuilding the Ariel, several relevant developments since my last real work on the Spitfire are that I now have a Sunnen hone and Magnaflux kit, as well as the ability to build up metal with Stellite, copper, and hard chrome.

BSA Service Sheet 702 lists the diameters of the bushes used in the various models and I have Sunnen mandrels for all of them (and many more, covering 0.106" to 4.2"), from the 0.218" speedometer spindle to the 2.756" cylinder bore. This should allow me to assemble the bike with a bit better precision than when it left the factory. Since finishing the gearbox is at the top of the list, the first component to benefit from the Sunnen will be the bush that fills half the sleeve gear (with a bearing in the other half).

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Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757190
11/26/18 3:42 pm
11/26/18 3:42 pm
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The real reason for soaking the gearbox covers for a full week is I "had" to make a three-day trip to France (nb. I'm sure there's a compound word in German, but I can't think of an appropriate English word for agreeing to do something that you enjoy doing). It was a bit chilly, but perfect for walking around the picturesque city of Besançon, and the ever-changing weather forecast managed to keep moving its 100% chance of rain predictions away from the times I would be outside.

Anyway, with France dealt with, I'm now back to dealing with the Spitfire. I've now learned from Kibblewhite that the Ariel valve blank I need is still backordered, reducing temptation to work on the Ariel even though I could usefully machine and install a new guide and do the final honing to size after the valve arrives.

Since no such guide seems to exist on the web I've started photographing the various components in order to produce a comprehensive "manual" over the next several posts for rebuilding pre-unit BSA gearboxes at the level of detail of my six-spring clutch thread

Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757258
11/27/18 2:29 am
11/27/18 2:29 am
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Before starting to document the assembly of my gearbox I skimmed through this thread to see what I had previously posted and was impressed to discover how much work I've already done. The nice thing about spreading a rebuild out over so many years is not realizing how much time has been squandered. Anyway, to (re)start the gearbox rebuild, this post contains some information that I don't think is commonly known.

There are four spacers critical to the smooth operation of T-type gearboxes that are not clearly illustrated in the parts manual so the first two images show their positions and thicknesses. It's important to note that #73 and #74 are not used in Standard-type gearboxes It might seem with 8 gears, some of which could be installed in either of two orientations, that getting the correct gears in the correct locations would be nearly impossible. However, it's actually not that difficult, and the second photograph should help make it even easier.

Because there is a slight taper, rather than a sharp edge, where the inside end of the layshaft meets the splines, and depending on production tolerances, that taper might extend slightly beyond the face of the gear (e.g. at the left side of the gear that's at the top of the third photograph, which has the spacer in question positioned against the face of the gear). A subtle point is both sides of the IDs of OEM spacers are chamfered allowing them to be installed in either orientation without hanging up on that taper. However, if an aftermarket spacer doesn't have the chamfer, or has it only on one side and is incorrectly oriented, the spacer might not sit flush with the gear. If this is the case the hardened spacer will have to be relieved by grinding before it is installed.

Unfortunately, a huge pitfall awaits someone assembling a gearbox from mixed parts because some of the "equivalent" gears in bush-type (e.g. STD2) and in T-type (e.g. ASCT, SCT2, etc.) have different widths. Referring to the standard BSA gearbox chart, note that gear 'B' on the STD2 and SCT2 both have 18T (although a closer look at the chart reveals they have different part numbers). Unless careful, even when holding the gears side-by-side you might not notice there's a difference, but the third photograph shows that gear B on the bush-type layshaft (at the bottom, with a scroll at the end of the shaft is narrower than that on the T-type layshaft (at the top, with a smooth end on the shaft).

Although I had never before taken the time to measure the width of gears, now I have, albeit only for one of each type, i.e. STD2 and SCT2. Although for some gears it's clear what is meant by the width, the fourth and fifth images show how I determined it in unclear cases. Although I measured each of the widths to 0.001", below I list the values rounded to 0.01" because with only two examples I don't want to imply precision that might not be present due to production tolerances.

__________ width
Gear_STD2 ___ SCT2
A ___ 0.68" ____ 0.70"
B ___ 0.70" ____ 0.78"
C ___ 0.88" ____ 0.85"
D ___ 0.59" ____ 0.60"
E ___ 0.68" ____ 0.86"
F ___ 0.94" ____ 0.93"
G ___ 0.86" ____ 0.86"
H ___ 0.54" ____ 0.54"

As can be seen from the above values, both B and E are different between the two types of gearboxes,(*) although the 0.03" discrepancy of C must be within the production tolerance as can be deduced from comparing part numbers. As a result, to assemble a gearbox from mixed parts requires a set of calipers along with the usual sockets and spanners.

(*)Note: I came across an unattributed reference that gives different figures than above, which means they used different points across the teeth for measurement, and also says that Gear A is wider for the T-type gearbox as well (although it doesn't mention E as being different). Although this might seem to be confirmed by the different part numbers for A for the two gearboxes I measured, A is a special gear for the SCT2 since it contains a needle bearing so it would have a different part number no matter what. However, it's even more complicated for earlier gear sets. For example, the RR and RRT used the same 25T Gear A as each other (but different than in later gear sets), as do the DAY and DAYT for their 26T gear (again, different than in later gear sets). In all the chart has five different part numbers each listed for 25T and for 26T Gear A. Clearly, what is needed is a table of widths, all measured in the same way, for all the gears BSA used over the years. Unfortunately, this is greatly complicated by the fact in most cases gearboxes might have been rebuilt at some time in the past 60 years using one or more incorrect gears, coupled with the fact there are no part numbers on the gears.

Attached Files Gearbox_assembly_001.jpgGearbox_assembly_002.jpgGearbox_assembly_003.jpgGearbox_assembly_004.jpgGearbox_assembly_005.jpg
Last edited by Magnetoman; 12/03/18 11:00 pm. Reason: added text about Fig. 1 only applying to T-type gearboxes
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757375
11/28/18 4:55 am
11/28/18 4:55 am
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Magnetoman Online content OP

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Originally Posted by Magnetoman
I skimmed through this thread to see what I had previously posted and was impressed to discover how much work I've already done.
A friend called today and pointed out I also had contributed material to a gearbox 'sticky' thread on the Gold Star forum, which I'd also forgotten about. Sigh...

He also suggested that instead of hiding my gearbox rebuild in this thread about an obscure model, I should make it stand-alone so it would be easier for BSA owners to find it later. That's an excellent suggestion, that I agreed to, but upon reflection and review of what I've already written, I'm going to implement a modified version of his suggestion. I'll continue with the rebuild here, while off-line I'll start organizing a stand-alone rebuild thread that will include this material, and more, although organized in a straightforward way. Also, since I'm now at the point of putting the Spitfire's gearbox back together, I'll need to document taking another one apart to have a complete thread anyway.

When I took the gearbox components out of the bucket of diesel+Gunk I noticed a couple of cracks in the lid. Since they could have let rain water in I bought a new bucket and decanted the old one into it. The first photograph shows the dregs, which must be congealed grease. Interestingly, even though I haven't cleaned very many things in that bucket the mixture has managed to remove ~25 cu.in. residue, which speaks well of the cleaning power of this solution.

As I took them out of the bucket I spent maybe two minutes each on the three gearbox castings with #0 Medium Fine stainless steel wool, followed by washing with soapy water and paper towels. Although a difference in reflectivity of only a few percent makes a big difference visually, it's difficult for a camera to capture. The best I could do was to position the cleaned SCT2 casting with an uncleaned one to directly reflect sunlight. As the blown out highlights in the second photograph show, that nearly obscure the 'T2', the casting I cleaned with very little effort is significantly more reflective.

The next step in the rebuild will be to replace the sleeve gear bearing and seal. These are held in place with an internal retaining ring that doesn't have holes for using "standard" retaining ring pliers, as shown in the next photograph. While it's relatively easy to worry the ring out of the groove using a pick or small screwdriver, getting it back in again can be quite a hassle. The next two photographs shows a "tool" I made that makes this job much easier. I get one end of the ring started in the groove then while pushing down I"walk" the tool around it to push it into position, sometimes helped by pushing inwards on the ring from the side with a thin screwdriver.

Attached Files Gearbox_assembly_006.jpgGearbox_assembly_007.jpgGearbox_assembly_008.jpgGearbox_assembly_009.jpgGearbox_assembly_010.jpg
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757397
11/28/18 10:03 am
11/28/18 10:03 am
Joined: Sep 2004
Posts: 900
Farnham, Surrey, UK
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Interesting degreasing solution, what's the ratio of diesel to gunk and what type of gunk are you using?


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: 1957 BSA Spitfire Scrambler [Re: gunner] #757422
11/28/18 3:46 pm
11/28/18 3:46 pm
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Originally Posted by gunner
what's the ratio of diesel to gunk and what type of gunk are you using?
I thought I had described it earlier in this thread, but instead it is here. Since I wrote that post I learned diesel is available in at least two mixes with #2 specified for modern cars (which is what I used) and #1 having a higher ratio of kerosene in it (which is what I would have used if I had known about it and could find it). Unfortunately, a quick search didn't show any sources of #1 where I live, although it may be so common at truck stops that no one bothers to explicitly list it. However, I wouldn't dump out my current mix even if I did find #1 now. Also, as a friend in New York recently discovered, diesel fuel begins to congeal at ~32 oF and gels at ~15 oF, so those of you who live in colder climates will have to keep your 5-gal. bucket of degreaser in the kitchen if you want to use it over the winter months.

Originally Posted by gunner
I don't think the wife would be too impressed with a bucket of degreaser in the kitchen!
I haven't tried, but I bet it would work better than any standard kitchen detergent on pots and pans.

Last edited by Magnetoman; 11/28/18 4:25 pm. Reason: corrected #1 and #2 plus gunner reply
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757427
11/28/18 4:09 pm
11/28/18 4:09 pm
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Posts: 900
Farnham, Surrey, UK
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Great, thanks for that MM I will try my own experiment with Diesel/Kerosene and use the one of the Gunk formulations available in the UK.

You seem to have had very good results which is something I want to try and replicate.

Luckily my garage is attached to the house so it never gets below freezing & I don't think the wife would be too impressed with a bucket of degreaser in the kitchen!


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757457
11/28/18 8:36 pm
11/28/18 8:36 pm
Joined: Feb 2014
Posts: 497
Cork Ireland
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Hi MM and All,
In photo four in above in post 737573 showing the "tool" and circlip

This photo shows a very common error !!!!!!!!!
The circlip is not fully seated opposite its open ends
It should be Concentric with the seal step and casing bore
The inner face of the seal has rings of the sealing material standing proud of the base material
These have to be compressed in order to get the circlip to seat fully
It can be a real struggle to get the circlip fully seated on some (most) gearboxes!!
Clamping the assembly usually grips the circlip and does not allow it to expand
Working around the circlip circumference with a blunt ended brass punch and small hammer helps then you may
also work on the circlip ends to "encourage" it to seat fully

Almost all the BSA gearboxes I have worked on have arrived with the above problem and oil leaks to go with it
On one particularly stubborn box I had to resort to sanding the inner face of the seal in order to seat the circlip

John

Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757469
11/28/18 10:30 pm
11/28/18 10:30 pm
Joined: Jun 2018
Posts: 38
Rabbit Creek, Alaska, USA
Jay Gilling Offline
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Originally Posted by Magnetoman
Originally Posted by gunner
what's the ratio of diesel to gunk and what type of gunk are you using?
I thought I had described it earlier in this thread, but instead it is here. Since I wrote that post I learned diesel is available in at least two mixes with #2 specified for modern cars (which is what I used) and #1 having a higher ratio of kerosene in it (which is what I would have used if I had known about it and could find it). Unfortunately, a quick search didn't show any sources of #1 where I live, although it may be so common at truck stops that no one bothers to explicitly list it. However, I wouldn't dump out my current mix even if I did find #1 now. Also, as a friend in New York recently discovered, diesel fuel begins to congeal at ~32 oF and gels at ~15 oF, so those of you who live in colder climates will have to keep your 5-gal. bucket of degreaser in the kitchen if you want to use it over the winter months.

Originally Posted by gunner
I don't think the wife would be too impressed with a bucket of degreaser in the kitchen!
I haven't tried, but I bet it would work better than any standard kitchen detergent on pots and pans.



Home heating oil has the kerosene mix which you can just buy separately as well. As far as diesel gelling in cold climates, You can also just buy a bottle of diesel antigel and mix it in. I keep some diesel with 6 oz of antigel outside in a shed that reaches -30F -40f just as a back up for a generator and there are no issues.


'67 BSA 441 Victor Special
'73 Triumph T140V
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757472
11/28/18 10:48 pm
11/28/18 10:48 pm
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Originally Posted by chaterlea25
This photo shows a very common error !!!!!!!!!
That's a good point and in light of your comment I should have noted the issue in my original post. I took an empty housing from the shelf to use to make that shot of the tool, and the fact the tool isn't sitting flat in the last photograph of that post certainly shows the snap ring in that housing isn't properly seated.
Originally Posted by chaterlea25
It can be a real struggle to get the circlip fully seated on some (most) gearboxes!!
+1 on that observation. Even on "easy" gearboxes it's a struggle, which is why I made that tool.

Showing one of the landmines that awaits a rebuilder, the only gear in my SCT2 that has a part number on it is H, shown in the first photograph. However, 42-3082 does not appear anywhere on BSA's gearing chart. Unless someone had a BSA 'Master Priced List' from later than 1959 they wouldn't know that this number was superceded by 42-3210, which is on the chart as the correct gear for an SCT2.

Back to assembling the gearbox. If there is excessive wear of any of the bushes (or sleeve gear needle bearing, in the case of the RRT2/SCT2), press the old one out and the new one in. You may have to ream or hone the new bush after installation. These finer points of assembly will be discussed later in an Appendix.

During inspection of the components note that the layshaft is hollow and has a number of holes for feeding oil to the gears as shown in the second photograph. Even if you didn't press gear B off and back on again, make sure that its oil hole is lined up with the corresponding oil hole in the shaft. Also, as better seen in the inset, there is a steel "O-ring" under the dogs that serves to locate the position of the gear when pressed onto the shaft. Make sure it is present and that the position of the gear on the shaft with respect to it is as shown in the photograph.

As shown in the third photograph, if you need to replace the sleeve bearing remove the circlip with a screwdriver (or two), then remove the oil seal. Clean residual oil off as best you can to reduce the smell and heat in an oven to ~225 oF. The bearing may fall out at that point when rapped against a wood table, but have a suitable drift ready in case it needs a few taps. The fourth photograph shows a 1-5/16" socket with extension that would work as a drift.

The final photograph shows that the 'tophat' shape of the bush in a bush-type gearbox housing serves as a stop to locate the in-out position of the bush, but be sure to install it with the oil hole facing the drilling in the housing. If you are replacing the bush it's convenient to have everything ready to press it into place while the housing is still hot. This photograph also shows that the needle bearing in a T-type gearbox is installed with its outer edge flush with the countersink in the housing. I note this because Torrington recommends having it protrude by a certain amount. As is the case with a bush, make sure the oil hole in the needle bearing is aligned with the hole in the housing.

Originally Posted by Jay Gilling
Home heating oil has the kerosene mix which you can just buy separately as well.
You can also just buy a bottle of diesel antigel ... shed that reaches -30F -40f
Thanks very much for that information which will be quite helpful for those in colder climates. Heating oil and -40oF temperatures aren't experienced where I live, but I wonder how much the cleaning effectiveness might be reduced even if the diesel doesn't gel. I'm sure my friend will head straight to the diesel supply store to buy some of that magic antigel, and then report back if it still cleans in a New York minute... er, I mean winter.

Attached Files Gearbox_assembly_011.jpgGearbox_assembly_012.jpgGearbox_assembly_013.jpgGearbox_assembly_014.jpgGearbox_assembly_015.jpg
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757517
11/29/18 2:43 pm
11/29/18 2:43 pm
Joined: Jun 2018
Posts: 38
Rabbit Creek, Alaska, USA
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No need to go to a fancy diesel supply store , every Home Depot or Walmart sells it.Power Service in the white bottle or Howe’s Diesel Treat. I would think it might clean even better thinned out a little with the dispersants. That looks like it’s coming together nicely.


'67 BSA 441 Victor Special
'73 Triumph T140V
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757525
11/29/18 4:28 pm
11/29/18 4:28 pm
Joined: Aug 2013
Posts: 25
England
Servodyne Offline
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Hello Magnetoman it's good to hear that you have started up your fascinating thread again on the 57 Spitfire. I have been reading it with interest since buying my 57 Spitfire from Paul67 who contributed to the thread way back in 2013/14.
I bought the Spitfire as a project and it had been assembled with upswept pipes and 3/4 seat, but I wanted it to be it as close as possible to the original 57 spec but with a bit of room for individuality. I got it up and running last year and I love it, but regret not having the crank balanced as I would like to enjoy more of it's performance. I've recently bought an early heavy crank, which may have been correct for 1957, so I may prepare that with billet rods and 9:1 pistons and get it balanced in readiness for a swop over in the future.

Jim

https://www.youtube.com/watch?v=IMpF7ZD4GN8&list=LLn6l8XGJ6EyXLrc50lQzNWA&index=2&t

Last edited by Servodyne; 11/29/18 4:31 pm.

1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando
1961 Norton 99
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757583
11/30/18 4:10 am
11/30/18 4:10 am
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Magnetoman Online content OP

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Originally Posted by Servodyne
. I got it up and running last year and I love it,
Congratulations on a bike that looks and sounds so great. With those pipes, your neighbors much love you.

It's unlikely there will be a problem with the selector quadrant in the middle cover, but if there is the gearchange bush will have to be pressed out, which is best done after heating to ~250 oF. While it is hot also would be a good time to replace the layshaft bush and main shaft ball bearing (standard gearbox) or needle and ball bearing (T-type), if they are worn. If you install a new bush make sure it has the correct clearance. The end of the selector quadrant spindle that's exposed after removing the gearchange bush is threaded 1/4-26 BSF and should be a slip fit. If so it can be withdrawn by hand, although a spacer may be needed if force is required.

Check the fit of the sleeve gear on the main shaft, paying particular attention to this if you have renewed the two bushes that are in it, with a gap between them. If the gear is too tight on the shaft you risk having it seize. If the sleeve gear is for a standard gearbox there will be three oil holes (at 12:00, 4:00 and 8:00 in the photograph) that need to align with the holes in the bush that's nearest the camera. A second bush has no oil holes. If it is an RRT2 or SCT2 there only will be one hole in the face of the gear (shown at 12:00) that has to align with the hole in the needle bearing. Like the other type of sleeve gear there is no oil hole in the bush at the other end of the gear.

Thanks to aftermarket parts, the next step may be the most difficult in any rebuild. I've only measured one gearbox housing so I don't know how much variation there is due to BSA's production tolerances, but in my case I found the following dimensions:

Height of bottom of retaining ring groove above top of Hoffmann bearing: 0.054"
Width of retaining ring groove: 0.074"
Thickness of retaining ring: 0.069" (i.e. this gives it room to move upwards in the groove by 0.005" if forced)
Thickness of the old Hoffmann oil seal: 0.059"

From the above you can see that after installing the 0.059"-thick original oil seal the retaining ring just (barely) fit in the groove with 0.000" additional clearance. The problem is the aftermarket oil seals I have are 0.077" thick, i.e. fully 0.018" too thick to have any chance of installing the retaining ring. And, no, there's no way the rubber coating could be compressed by anything close to this much. As an aside, the metal on both seals is 1.0 mm so the problem is an excess thickness of the rubber coating on the aftermarket oil seal.

I don't have a photograph to show it, but I suggest a trial installation of the retaining ring without the seal in place in order to measure the gap between the ends when you know it is fully seated in the groove. This will give you a value to compare against when you repeat it with the seal, so you will know whether or not the retaining ring is properly seated. In my case the gap was ~5 mm.

I pity the poor rebuilder who doesn't have a lathe, but after removing the excess 0.018" thickness of rubber using a combination of the lathe and 100-grit abrasive paper, and using the tool I showed in an earlier post I was able to install the snap ring with a minimum of hassle. Because of the 0-thou. clearance I worked my way around the seal's housing applying light pressure from a screwdriver blade to get the retaining ring fully into its groove, with the result shown in the final photograph.

Attached Files Gearbox_assembly_016.jpgGearbox_assembly_017.jpgGearbox_assembly_018.jpgGearbox_assembly_019.jpgGearbox_assembly_020.jpg
Last edited by Magnetoman; 11/30/18 2:42 pm. Reason: added text about bush clearance
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757597
11/30/18 10:09 am
11/30/18 10:09 am
Joined: Sep 2016
Posts: 178
County Durham
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ducati2242 Online content
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County Durham
I thought I must have been doing something wrong when I was trying to fit that seal . I didn't have the gearbox out and was trying to do it in situ . Luckily I do have a lathe and did similar to yourself but couldn't measure it as well . I always had doubts about what I did but seeing your work puts my mind at ease . Thanks for this .

Re: 1957 BSA Spitfire Scrambler [Re: ducati2242] #757667
11/30/18 9:00 pm
11/30/18 9:00 pm
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Posts: 497
Cork Ireland
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Hi MM and All,
There is probably a "tolerance" in the housing depths or circlip groove location ????
Only on one occasion have I had to resort to thinning the seal down
I believe that some compression of the seal face is required to prevent oil leakage
Measuring an old seal that has been previously fitted (compressed) may lead to unknown unknown's ??
With zero compression of the seal it may rotate in use!!

John

Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757704
12/01/18 4:50 am
12/01/18 4:50 am
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Magnetoman Online content OP

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Originally Posted by chaterlea25
With zero compression of the seal it may rotate in use!!
Even with the tool I made I had to push hard to get the retaining ring into the groove so there's no chance it will rotate. Also, in what I prefer to think is belt 'n braces rather than OCD, there's gasket cement between the seal and bearing.

For those who are interested in such things, on the durometer A scale the rubber on the old seal measures 94 and the new seal 80. For comparison, my Ariel's front tire is 65. The high durometer value is why the ~0.020" thickness of the rubber on the back of even a correctly made new seal can be compressed very little by anyone other than Superman.

Speaking of sealing, the next thing to check in a gearbox rebuild is the condition of the sealing surface of the sprocket since it is subjected to an abrasive mixture of dirt and oil. As a result, in addition to the pits in the surface, the sprocket on the left in the first photograph has a groove 0.007" deep worn into it. A rough surface like this will quickly abrade away a new seal so either needs to be reconditioned, or replaced.

The second photograph shows the what is needed for the next step of installing the sleeve gear. I use a chain wrench I made with drive chain at one end and primary chain at the other end. Also, I made a sprag socket so I can use an impact and/or torque wrench on the nut, although the classic tools are a punch and big hammer.

However, this is as far as I got today because my older daughter called with a 55-gallon leaking fish tank emergency. Not counting the ~40 lbs. of rocks in the bottom or the weight of the stand the tank sits on, the water alone weighs 450 lbs. Siphoning, bucket carrying, and fish wrangling used up the rest of the day.

Attached Files Gearbox_assembly_021.jpgGearbox_assembly_022.jpg
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757718
12/01/18 11:54 am
12/01/18 11:54 am
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Farnham, Surrey, UK
gunner Online content
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Hi MM, I realise you are keen on keeping the bike original as possible but was wondering if you had considered using a sealed bearing in the gearbox instead of an open one? It would be hidden from view and will stop any leaks so worthwhile in my view.

SRM sell a gearbox sprocket nut with a built in seal designed to stop leaks from the mainshaft, see This Link, so maybe worth considering.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757730
12/01/18 3:22 pm
12/01/18 3:22 pm
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Originally Posted by gunner
Hi MM, I realise you are keen on keeping the bike original as possible but was wondering if you had considered using a sealed bearing in the gearbox instead of an open one? ... SRM sell a gearbox sprocket nut with a built in seal ...
Quoting from SRM's web site the nut will help reduce the oil weep from the gearbox mainshaft when the bike is standing on its side stand, However, like other Gold Star frames produced prior to late 1957, the Spitfire doesn't have a side stand lug. My BB and Catalina also only have center stands, don't leak from their gearboxes when parked, and the oil consumption when under way is acceptable as well.

On a more fundamental level, the "problem" with something like the SRM nut is my compulsion to try to keep the bike as original as possible, whether or not any particular item can be seen (if anyone is aware of inconsistencies with this statement in this thread, please spare me the embarrassment of pointing them out). It's not a question of cost since I bypassed a new sealed bearing that was part of a hoard that came to me a few years ago and instead installed a used Hoffmann that also was in that hoard

Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757751
12/01/18 8:27 pm
12/01/18 8:27 pm
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Hi MM and All,
When an impact wrench or long lever is used with a "proper" tool to tighten the gearbox sprocket nut,
it can cause the inner diameter of the sleeve gear bush to close up at the outer end a thou or two
Enough to cause seizure in use!!!

DAMHIK
John

Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757763
12/01/18 9:40 pm
12/01/18 9:40 pm
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Originally Posted by Magnetoman
I made a sprag socket so I can use an impact and/or torque wrench on the nut, although the classic tools are a punch and big hammer.
Originally Posted by chaterlea25
When an impact wrench or long lever is used with a "proper" tool to tighten the gearbox sprocket nut,
it can cause the inner diameter of the sleeve gear bush to close up at the outer end a thou or two
That's an excellent point, well worth noting.

I have one battery and three pneumatic impact drivers with claimed max. torques of 75, 225, 320, and 700 ft-lbs. Since none are adjustable, the only safe way to use any of them is for removing fasteners. Or for installing fasteners that require higher torque than the max. rating of a given impact driver, followed by a torque wench. The battery-powered one I had along on the Cannonball made me nervous for this reason because it is so easy and convenient to use, but it has a max. torque of 225 ft.lbs. that is ~3x higher than any torque specification on any of our motorcycles other than crankpin nuts.

There will be another work stoppage of a few days, not due to industrial action, but due to grandparenting duties.

Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757876
12/02/18 7:53 pm
12/02/18 7:53 pm
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While mostly on grandparenting duty today I did manage to sneak into the garage to make a few photographs and measurements. The guy who hoarded the hoard of BSA singles parts that I now hoard didn't seem to throw anything away, no matter how worn. As a result I have 14 spare gearboxes, some of which are assembled or partially assembled. However, of the seven cases that were empty or easy to empty, two have cracked housings under the sleeve gear like that shown in the first photograph.

You might think I'm no better than the previous hoarder was since I haven't thrown out these cracked cases. Although you might be right, in my defense, if these were for a machine for which parts were hard to come by these cases could be repaired to be fully functional by TIG welding and machining. However, for present purposes the important thing is to note that the casting around the bearing is pretty thin and my best guess from the nature of the damage is it was caused by someone hammering the bearing out without having heated the case.

If you heat a gearbox casting to ~225 oF to install the sleeve gear bearing the ~0.0053" thermal expansion of the 2.83" ID cavity is enough that a room temperature bearing will fall to the bottom of the recess under its own weight, requiring no help from a drift. However, if you do this to remove a bearing that's already installed the steel bearing also expands. But, because the bearing expands at a slower rate than the AL, the differential expansion is ~0.0023". The fact it requires a few gentle taps on a drift to remove a bearing this way says the interference fit at room temperature must be ~0.002"-0.0025". I'd have to deploy the inside micrometer for a quantitative check, but this value has to be very close.

If you decide not to bother heating the casting before removing the bearing, look at the first photograph and reconsider your bad decision before you regret it.

Looking at all of these cases lined up on the bench I see data points waiting to be gathered. I only had time to make quick measurements, but they seem to show the distance from the face of the housing to the large diameter faced region around the layshaft bush/bearing is 4.5". As the second photograph shows, because of variations in the castings, to achieve this result required removal of different depths of material. I'll be making much more careful measurements of this dimension to confirm this is the case, and to determine how much production variation there is since in the end that determines the spacers required to give the proper layshaft end float. Also, since the only difference between the standard-type and the T-type housing is in the layshaft bush/bearing, and since the bearing requires a larger diameter hole, it is easy to convert from one to the other. Or back again, with a bespoke bush having a thicker wall.

Anyway, as soon as I get back in the garage I predict I'll head down this rabbit hole for a little while.

Attached Files Gearbox_cracked housing.jpgGearbox_back face.jpg
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #757962
12/03/18 4:25 pm
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As can be seen from the 2nd photograph of my previous post, the area around the bush/needle for the layshaft has two circular regions cut into it. Call these InC and OutC. I measured the ODs of one each of these on a standard and on a T-type housing and found the InC 1.268" on both and the OutC 2.001" and 2.025". These dimensions aren't critical since they just need to be larger than the 1.175" OD of shim #73 and the 1.963" OD of the larger of the two possible Gear B, 18T.

Next, using a depth gauge of better precision than needed, supported on the face of the gearboxes by Brown & Sharpe 'Ultra-Precision' parallels of measured heights 1" to better than 0.0005", and at a garage temperature a frigid 62 °F, I measured the depth below the face of the cases of those two circular areas.

The depths of OutC below the face of the gearboxs for the two T-types that I measured were 4.509" and 4.525". For the four standard type the depths were a bit less at 4.455", 4.484", 4.492", and 4.499". However, given the almost-overlapping ranges it seems BSA was aiming for 4.500" for this depth for both types of gearboxes.

As for the InC, although both types of gerboxes have the same ~1-1/4" OD, the depths are different for the two types. The two T-types I measured were 4.577" and 4.580" while the two standard types were ~0.060" less at 4.518" and 4.522" (the other two housings had bushes installed so I didn't measure them). Although I only have two data points for each type, this difference seems significant since the different widths of gear B causes the face of the T-type gear to be ~0.08" closer to the end of its layshaft.

Before I emerge from this latest rabbit hole I'll have to press a "tophat" bush out of one of the cases and measure the thickness of its "brim" since along with shim #73, the depth of InC, and to-be-measured possible differences in the layshafts, it determines the gap to the face of Gear B, i.e. the end float of the layshaft.

Aside from the depth of InC the only other difference between the cases is the 7/8" (nominal) diameter of the hole for the press fit bush and the 1" (nominal) diameter of the hole for the press fit needle bearing. So, subject to someone pointing out something obvious I missed, the only two things that need to be done to convert a standard gearbox housing to a T-type are to skim an additional ~0.06" from InC and ream the hole larger for the necessary press fit of a needle bearing. Both are very easy operations on a milling machine.

Attached Files DepthMicrometer.jpg
Last edited by Magnetoman; 12/03/18 4:33 pm.
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #758109
12/04/18 3:26 pm
12/04/18 3:26 pm
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To return to an earlier subject for a moment, in looking for gearbox parts to measure I found a middle casting with the same sort of damage as I noted in several main castings. As the first photograph (again) shows, if you need to remove the bearing from any Al casting you first need to heat it to ~225 °F before you then gently tap the bearing out. The same for installation, although it probably will fall into place under its own weight.

As the 2nd photograph shows I used old fashioned analog technology to measure the lengths of one Standard-type and two T-type layshafts. For the Standard-type the faces of the top hat bushes at either end of the layshaft serve the purpose of thrust washers so neither #73 nor #74 from the first figure in an earlier post is used.

As shown, placing the layshafts upright on accurate 1.000" parallels I used a vernier height gauge to make measurements from the outer surface of Gear B (Standard type) and the outer surface of thrust washer #73 (T-type) to the outer surface of Gear H, i.e. without the 0.113"-thick thrust washer #74. The Standard type layshaft was 4.392" long but the T-types (with #73 in place) were 4.561" and 4.575" long.

As the 3rd photograph shows, the surface in the middle casting against which #74 sits is recessed from the face by approximately the thickness of that thrust washer. In two of the three T-type castings the washer sits 0.006" and 0.0015" below the surface and in the third it is 0.0015" above the surface. The bush in the single Standard-type is 0.005" above the surface, i.e. it has the same thickness as #74 within BSA's apparent production tolerances (the bush measures ~0.116" with calipers vs. 0.1125" for #74 with a micrometer). From these measurements I infer that BSA intended for that recess to be 0.1125" below the surface of the middle casting for both types of gearboxes.

Another aspect that will contribute to end float is the thickness of gasket #46 that sits between the two castings. I don't know how thick the original BSA paper gaskets were but I have a few that might be OEM along with a bag of aftermarket composite gaskets. The uncompressed paper ones are 0.010", the blue composites are 0.016" and the red composites are 0.018".

Putting together information from the past few posts, for the T-type:

Distance of the inner machined circle (against which #73 sits) to the face of the casting: 4.577"~4.580"
Length of T-type layshafts with #73 but without #74: 4.561"~4.575"
Thickness of gasket: 0.010"-0.018" (or ~0.002" if only gasket sealer is used)
Clearance for layshaft in middle casting with #74 in place: from +0.006" to -0.0015"

If all the components are at the ends of their tolerance ranges needed to give max. end float, the end float will be:

4.580" - 4.561" + 0.018" + 0.006" = 0.043"

If, instead, the tolerances conspire to give min. end float, the end float will be:

4.577" - 4.575" + 0.002" - 0.0015" = 0.0025"

It should be emphasized that these variations came from just the few components I measured. If I had measured more components almost certainly the range of variations would be larger.

My measurements on the Standard type aren't as precise because I didn't press the top hat bushings out of the cases to accurately measure the thickness of their brims. However, my measurements with calipers on two of them should be accurate to ~0.002". I only measured one Standard-type layshaft and found it to be 4.392" (without #73 or #74 since neither belong on this type of layshaft) so:

Distance of the inner machined circle (against which bush #77 sits): 4.518"~4.522"
Thickness that the rim of bush #77 sits above the surface: 0.071"~0.090"
Length of Standard-type layshaft without either #73 or #74: 4.392"
Thickness of gasket: 0.010"-0.018" (or ~0.002" if only gasket sealer is used)
Clearance for layshaft in middle casting: -0.005"

If all the components are at the end of their tolerance ranges where they give max. end float, the end float will be:

4.522" - 0.071" - 4.392" + 0.018" - 0.005" = 0.072"

If, instead, the tolerances give min. end float, the end float will be:

4.518" - 0.090" - 4.392" - .002" - 0.005" = 0.029"

In both cases it would seem the addition of a a thicker thrust washer would be needed to get to the BSA's specified range of 0.010"-0.020". Which end of the layshaft such a hardened washer should go on would have to be decided after trial assembly and inspection through the cover.

As can be seen from this, given the variations I found in the components I measured, achieving BSA's recommended end float of 0.010"-0.020" either requires considerable luck, or trial fitting and measurement. The gasket used (or not used) is the biggest and easiest variable over which the rebuilder has control. Once the adjustment possible with gaskets is used up, look into using thrust washers of different thicknesses. The Standard-type gearbox also allows adjustment of the end float using bespoke bushes with appropriate brim thicknesses.


Attached Files Gearbox_BrokenMiddleCasting.jpgLayshaft_length.jpgMiddleCover01.jpgMiddleCover02.jpg
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #758314
12/06/18 2:50 am
12/06/18 2:50 am
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Since one can't have too many special tools, and since I know a friend is going to need them in the future, I took time today to make drifts for removing and installing the bearing/bush in the main gearbox housing and in the central casting. They're sized to work both on needle bearings as well as bushes.

On the subject of bushes, one of the first things I did was to heat a case and use one of the new drifts to drive the bush out so I could measure the thickness of its brim. It is 0.111", which is essentially the same as the thickness of thrust washer #73 (0.108") of a T-type gearbox. However, this does not mean the inside face of Gear B for both types of gearboxes starts out the same distance from the housing because the recesses in the housings (that I termed 'InC' in an earlier post) have different depths. I'll return to this point in what follows.

Since the depth of 'InC' is a critical difference between the two types of gearboxes I took the time to very carefully measure it again. I laid out three each of both types of gearboxes and, after checking the calibration of my depth micrometer, measured them at several points inside the recess. For the T-type I measured 4.5770", 4.5812" and 4.5816" for an average of <4.5799">. For the Standard type I measured 4.5170", 4.5182" and 4.5183" for an average of <4.5178">. These show that the InC recess is 0.0621" deeper (call it 0.062"+/-0.001") on a T-type gearbox than on a Standard type.

Note on thermal expansion: Although thermal expansion has an effect on the results on a 4½" Al piece made with a steel micrometer, the difference between measurements made at, say, 60 °F and 75 °F only will be ~0.0005". Still, whenever possible, one should avoid depending on the difference between two large numbers in a machining operation so it would be better to 'zero' at the current surface of InC and then move by 0.062" instead of 'zeroing' at the face of the gearbox and moving 4.580".

Remeasuring Gear B, it is 0.080" thicker on the T-type. The recess in its housing is 0.061" deeper, and thrust washer #73 is the same thickness as the brim of the bronze top hat bush in a Standard type, so this leaves ~0.020" unaccounted for. To get to the bottom of this I measured both types of layshafts gear-by-gear.

As the second photograph shows, after using a flat to make the outside faces of Gear B flush with each other, it can be seen that Gears B+D of the T-type (at the top of the photograph) are still thicker than the Standard type. In fact, the pair is now 0.098" thicker than on the Standard, so we seem to be going in the wrong direction. Don't give up, though.

Making the same measurement on B+F the T-type still is thicker by essentially the same amount (0.095"). However, finally, for B+H the difference is 0.058", i.e. the same amount as the "extra" depth cut into the T-type housings.

Since Gear H and spacer #99 are the same for both gearbox types, the difference must be in the layshaft itself. And, it is. As the third photograph shows the distance from the face of Gear B to the splines against which #99 presses on the T-type layshaft is 3.778". On the Standard-type it is 3.718", for a difference of 0.060". This is the amount by which the face of Gear B on the T-type gearbox has to be closer to the main gearbox housing in order for the face of Gear H to be the necessary 0.113" from the recess in the middle casting. The gears start out at different distances from the main case because of the extra ~0.060" depth, increase those differences as gears are added, but both end up with their Gear H at the same distance because the length to the end of the splines on the T-type layshaft is shorter than on the Standard layshaft.

Another nice feature of the measurements on the two layshafts is they quantitatively confirm the extra 0.061"+/-0.001" depth found with a depth micrometer on the T-type housing within the combined overall uncertainty of ~+/-0.002". Measure twice, cut once...

The second difference between these two types of gearboxes is shown in the fourth photograph. At the top is shown a 1.007"-diameter steel cap of thickness 0.082" (I only measured one cap, but two housings) next to the 1"-diameter recess (0.9986" and 1.0042") of depth 0.150" (0.140" and 0.156") into which the cap is pressed. The cap did not come from this particular gearbox, which can be seen to have a closed-end needle bearing in it rather than the open-end bearing which I believe is what was supplied by the factory. Hence, the need for a cap to keep the oil in.

As can be seen, no such recess for a cap is in a Standard type gearbox. However, the holes for both types are reamed 0.875"-dia. for a ~0.002" press fit with the bearing or bush. The photograph shows a reading of 0.8749" although the bore fluctuated by ~0.0005" along the length. In another gearbox the bore averaged 0.8762" which would have resulted in a press fit of only 0.0005"-0.001" with the OD of a Torrington bearing.

To summarize, the four differences I found between the two types of main gearbox housings are that in a T-type: 1) the inner recess for the layshaft into which thrust washer #73 fits is 0.061" deeper than in a Standard type; 2) the outer recess is ~0.035" deeper, 3) a 1"-diameter recess ~0.150" deep is on the outside of the bore for the needle bearing to allow for press-fitting a 0.082"-thick steel cap, and 4) all T-type, not just the RRT2, are drilled and tapped in both locations for the indexing plunger.

Attached Files RemovalInstallationTools.jpgLayshaft_length02.jpgLayshaft_length03.jpggearbox_outside.jpgBearingBushingBore.jpg
Last edited by Magnetoman; 12/09/18 8:34 am. Reason: Added note on thermal expansion; added text on the 4th difference
Re: 1957 BSA Spitfire Scrambler [Re: Magnetoman] #758467
12/07/18 5:09 pm
12/07/18 5:09 pm
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Before putting away the seven gearbox housings neatly lined up on the workbench I used the opportunity to carefully remeasure the depths of the 'OutC',

For the three T-type these depths are 4.5078", 4.5272" and 4.5370" for an average of 4.5240". The variation is in the actual depths so call this 4.524+/-0.015". For three Standard type these were 4.4842", 4.4912" and 4.4964" for an average of 4.4905". Assuming the same production variation, call this 4.490+/-0.015". Thus, the depth of the OutC for the T-type seems to be ~0.035" greater than that of the Standard type, although the variations are at least half of that difference. Since OutC only provides clearance for Gear B the depth isn't critical, and the variation in the above measurements are consistent with this.

A fourth Standard type has no OutC machined into it, as shown at the left of the first composite, but there are signs that something trapped between Gear B and the case rubbed against it at some point in its life even though the ~0.11" brim of a proper top hat bush is thick enough that there would have been no contact with the gear itself. The depth of the untouched portion at the right of this case is 4.465" and that of the rubbed portion near ~8:00 is 4.453", i.e. shallower by 0.025" and 0.037", respectively, than they should be.

At the right of the first composite is another case that shows the tool bit machined the case over most of OutC but didn't touch part of it. The machined region is 4.484" deep and the untouched region is slightly deeper at 4.488". Along with the untouched region of the case at the left of the composite that's 4.465", this indicates variations in the castings were ~0.02" which sometimes placed the back face slightly further back than the reach of the cutting tool for OutC.

I rechecked the spacing between Gear B and the spline as shown in the third photograph of my previous post. The two T-types were 3.774" and 3.778" and the one Standard type was 0.061" shorter than the average of those two at 3.715". Since Gear B is a press fit there is room for a few thou. variation in these measurements between different layshafts. I also found a bare Standard layshaft and measured the distance shown in the second photograph as 3.680". This implies a bare T-type layshaft would be 3.690+0.061 = 3.751" so it's probably specified on BSA's production drawing as 3.750". Which means it's a reasonable guess that the 0.061"+/-0.002" difference I measured for the depth of InC, and for the Gear B-to-H difference, is actually on the drawings as 0.0625", i.e. 1/16".

Attached Files Gearbox_NoRecess02.jpgGearbox_StdLayshaft.jpg
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