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BSA A10 to A70 A65 crank conversion #757412
11/28/18 2:05 pm
11/28/18 2:05 pm
Joined: Aug 2013
Posts: 25
England
Servodyne Online content OP
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Servodyne  Online Content OP
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Having spent years looking for an A70 crankshaft for my A70 project I decided to bite the bullet and convert an A10 crank when I came across a very good example with large journals. After reading much reference material on the subject I came to the conclusion that there was not much to be gained from using an alternator A10 crank as the drive side shaft is exactly the same length as a dynamo version.
Here is my story;

[Linked Image]

The one thing I wanted to retain about the A70 layout was the 'improved' timing side main bush oil feed and location. My crankcases, although used, still had the original standard bush fitted which was only marginally worn. The needle roller inner sleeve I was thinking of using had a nominal 1.5" OD which was slightly bigger than the std crankshaft size of 1.4985 to 1.499". Therefore the original bush only required the slightest amount to be reamed out to restore the nominal 1.5 thou clearance.
As the thrust face on an A10 crank is of smaller diameter than the A70/A65 the first job I did was weld a annular ring around the existing thrust face so that when it was ground down along with all the journals it would be big enough to cover the entire thrust washer. The photo shows the finished item after grinding and as you can seen the original oil groove is still evident. The journal was ground to 1.250" nominal to give the desired bearing fit to the sleeve.

[Linked Image]

This photo shows the bearing sleeve fitted, after being heated slightly. The annular groove was made using a high speed disc cutter with two discs fitted, guided by two jubilee clamps. I put two holes in the sleeve, one to match the feed hole in the crankshaft and another 180 deg opposite. The theory is in the very unlikely chance it moves some/enough oil will still make it to the big ends through the remaining groove on the crank. This is one of Mr SRM's concerns about sleeving worn shafts. The big difference here is the sleeve will also be firmly clamped by the outboard thrust washer, pinion and worm nut so movement is extremely unlikely.

[Linked Image]
[Linked Image]
[Linked Image]

These photo's show the outboard thrust washer and pinion fitted. The standard A70 pinion which is different to the A65 had to relieved slightly so as not to bottom on the radius on the crank. In difference to the A70 thrust washer, mainly due to wanting it to firmly clamp the sleeve, mine fits over the diameter of the timing side bush journal and not the worm drive shaft. Also, I wasn't keen on the idea of shims under the thrust washer to control end float so I Installed the assembly in the crankcase and found that 8 thou" needed to be removed from the end of the bush to give me the desired 2 thou" of end float.

[Linked Image]
[Linked Image]
[Linked Image]

These photo's show the modifications to the drive side. Strangely the A10 drive side bearing has a 30mm journal which had to be ground down to 1.125" nominal as used on the A65/A70s. Luckily the spines for the A10 crank cush drive are the same as the A70/A65 sprocket and mine where in good condition. the only problem is that they do not extend far enough along the crank so I elected to modify the sprocket rather machine the crank. There should be more than enough engagement on the splines when compared to other makes. Two options that I heard of for accommodating the alternator rotor. Drill and tap for an extension bolt or the more elegant option of a sleeve nut as per Commando. The thread is 5/8" UNF as original. The sleeve nut shown in the photo's was way too long as it turns out so it was cut down virtually in halve whilst maximising thread engagement on the crank. A new keyway was machined at the end of the alternator shaft and fortunately is spot on to the original setting for timing purposes.
I decided to retain the original A10 flywheel as modifying a late A65 one which is slimmed down around the big ends was proving far too difficult. The first thing that had to be done was reduce the outside diameter to that of an A65/A70. Also to remove weight from the big end area I shaved down the sides to 35mm wide compared with 40 mm on the A65. The resulting assembly was parcelled off to SRM for dynamically balancing.

[Linked Image]

This photo shows the engine nearing completion. It's got the later A65/A70 conrods with the steel caps and original pistons, bought at great expense. I did worry that the 1mm shorter stroke would be noticeable, but it looks fine and the slightly lower compression will probably be of benefit.

Please Note; Some of the photo's look horrible and apparently covered in swarf, but it's only particles of dust picked up by the flash.

Thanks for reading, hope it may be of use to someone.


1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando
1961 Norton 99
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Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757431
11/28/18 5:00 pm
11/28/18 5:00 pm
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DMadigan Offline
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Curious why you decided to grind the drive side to fit the inch size bearing rather than boring the cases for the metric one? Metric bearings are easier and cheaper to come by.
Nice work by the way.

Re: BSA A10 to A70 A65 crank conversion [Re: DMadigan] #757449
11/28/18 7:10 pm
11/28/18 7:10 pm
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England
Servodyne Online content OP
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Basically I didn't want to modify the A70 crankcases in any way just in case I got hold of an A70 crank, which I have just recently albeit crazily modified but that's another story. Also I just happened to have a new original Goldie drive side bearing of the same imperial size with wide rollers and a lovely brass cage. The outer ring doesn't have a lip to control end float but then again A70s don't need this as the timing side bush takes control of all that.

[Linked Image]


1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando
1961 Norton 99
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757519
11/29/18 3:00 pm
11/29/18 3:00 pm
Joined: Jan 2003
Posts: 36
minnesota
chuckmn Offline
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My old friend George Helm used to convert all his rebuilds on A65 and A10s to the A70 crankshaft. All his flat track bikes were set up this way. After he passed and the shop was closed I ended up with the patterns and directions he had. His one big problem was finding a correct sized thrust washer, he had bought up all the BSA A70 washers he could find and then used a modified tractor washer.

Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757523
11/29/18 3:36 pm
11/29/18 3:36 pm
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England
Servodyne Online content OP
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Servodyne  Online Content OP
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I'm sure that it's the way to go if you retain the bush. It must help maintain good oil pressure, a bit like putting you finger over the end of a hose pipe. I'll certainly look into it when I strip my A10 down as I'm sure there's just enough room for a thrust washer without having to counter bore the crankcases and reduce bush width as on the A70.


1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando
1961 Norton 99
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757612
11/30/18 1:17 pm
11/30/18 1:17 pm
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Rotherham - S. Yorkshire
Allan Gill Offline

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Many thanks for creating this thread, I will print this off as I find it very valuable.

1) Was the sleeve nut something you bought off the shelf (Commando type etc?),

2) How did you lock the rotor in position? is there a key way to stop the inertia of the crank winding off the sleeve nut?

3) on the A70 type bearing plate you have, does this stay fixed to the crank and then spin within the recess in the crank case, or does the crank end spin within the spacer?

4) Theres an irony as your putting an A10 crank into a dove framed OIF, which is what I wanted to do laughing , do you know the paint colour? is it powder or wet paint? and where did you have it done?

5) I have just noticed that the frontal Key hole slot is missing on your A70 cases, Mark Parker welded his up after it cracking I believe, I wonder if the factory found this also... Your cases also look a bit beefier than the A65 ones.

6) Am I right in thinking that the A10 T-S journal is smaller than that of the A65? or have I miss understood that part of the post? I will be having mine end fed, but will have much the same movements otherwise as yourself on this subject

Again thanks for posting and excellent work!!


beerchug
Re: BSA A10 to A70 A65 crank conversion [Re: Allan Gill] #757658
11/30/18 7:41 pm
11/30/18 7:41 pm
Joined: Aug 2013
Posts: 25
England
Servodyne Online content OP
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1) The sleeve nut was based on the Commando but is slightly longer by about 5mm. A Pity that the A10 crank drive shaft is just too short otherwise a Commando one would do.

2) There's a new keyway a bit further up the shaft that locates the rotor. You can see it on one of the photos. A lock washer fits in the rotor key way in the normal way.

3) The 'bearing plate' or thrust washer is clamped to the crank by the worm nut. It then spins in the recess in the crankcase and controls the 2 thou" end float. see new photos

4) The frame is powder coated RAL7035 dove grey https://paintman.co.uk/shop/bsa-dove-grey/

5) Just checked similar picture of my 71 Firbird cases. They look pretty much to same. There is a key hole slot but it's to the rear of the main bearing. The cases may be beefier, they certainly look rougher and not as well fettled.
6) The standard A10 timing side journal is 1.375" whereas the A65/A70 is 1.5".

[Linked Image]
[Linked Image]
[Linked Image]


1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando
1961 Norton 99
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757759
12/01/18 9:16 pm
12/01/18 9:16 pm
Joined: May 2013
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Rotherham - S. Yorkshire
Allan Gill Offline

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Again brilliant information. The A10 crank should be an almost direct fit with the NKIB5907 combination bearing that has a 35mm ID or 1.377” so depending on the grind on the crank it would only need machining enough to size to be true.

Thank you for the paint tip, did you have yours sprayed?


beerchug
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757773
12/01/18 11:15 pm
12/01/18 11:15 pm
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NickL Offline
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Looking at those photo's seems like you may have a problem with the fitting of the oil pump,
that thrust seems to be proud of the case.
As for the setup improving oil pressure, it's marginal, the oil losses are still there as they were
with the bush, maybe a little more restricted. The main thing is you can set the endfloat without
splitting the cases and you are running less risk of the sometimes not so captive thrust washer
chewing up the inner case. Also you can run an MRJ1 1/8 drive side main which is cheaper.
Personally, i still think the best way to preserve oil pressure on these old heaps is to fit a full
flow cartridge or canister oil filter. The other thing is to spend time rebuilding the pump properly.


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757774
12/01/18 11:22 pm
12/01/18 11:22 pm
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DMadigan Offline
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I wonder if a better approach to the timing bush would be a two piece flanged bush inserted from each side with a small gap between for the oil passage? That way the thrust can be taken up by a bronze face on both sides rather than the bronze washer on the inside and the aluminum case on the outside.
There would be no problem with the bronze turning in the steel backing since the oil passes between them instead of through a hole. They would have to be align bored after installing but that is necessary with the single bush anyway.
End float can be adjusted with a shim between the outside thrust washer and crank.

Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757775
12/01/18 11:39 pm
12/01/18 11:39 pm
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NickL Offline
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The snag with that Dave, is the outer one of the pair would be very narrow by the time you've got the recess..
There is no problem running a hard thrust against the softer ally case and remember the natural thrust of the
engine is toward the timing side anyway.


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757808
12/02/18 8:39 am
12/02/18 8:39 am
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Rotherham - S. Yorkshire
Allan Gill Offline

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Nick, what’s your view of fitting a triumph style oil filter in the bottom of the frame so that the oil is filtered before hand instead of after. Easy enough to convert and I should think the head pressure/weight of the oil is enough to stop the pump starving of oil?

LP Williams triumph oil filter

Last edited by Allan Gill; 12/02/18 8:49 am.

beerchug
Re: BSA A10 to A70 A65 crank conversion [Re: NickL] #757814
12/02/18 10:15 am
12/02/18 10:15 am
Joined: Aug 2013
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England
Servodyne Online content OP
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Servodyne  Online Content OP
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Originally Posted by NickL
Looking at those photo's seems like you may have a problem with the fitting of the oil pump,
that thrust seems to be proud of the case.
As for the setup improving oil pressure, it's marginal, the oil losses are still there as they were
with the bush, maybe a little more restricted. The main thing is you can set the endfloat without
splitting the cases and you are running less risk of the sometimes not so captive thrust washer
chewing up the inner case. Also you can run an MRJ1 1/8 drive side main which is cheaper.
Personally, i still think the best way to preserve oil pressure on these old heaps is to fit a full
flow cartridge or canister oil filter. The other thing is to spend time rebuilding the pump properly.


The thrust washer does protrude by 3 thou" even though it looks more in the photo. However the thickness of the gasket and the foot of the pump have been suitably cut away' to give 10 thou" running clearance which should be ample barring some sort of catastrophic failure. I would have to disagree with you on the benefits of running this 'closed' system with that of the standard open ended bush. I would consider that the extra back pressure caused by the thrust washer forcing the oil to change directions twice through small running clearances should be well worth the effort. I do take DMadigan's point though about the thrust washer running on the machined face of the aluminium casing. Hopefully clean filtered modern oil should be the answer to that one. I fit paper cartridge filters to all my old British machines.

[Linked Image]


1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando
1961 Norton 99
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757873
12/02/18 7:34 pm
12/02/18 7:34 pm
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argyll. scotland, uk
gavin eisler Offline
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I hope you fitted the DS rear engine plate and puzzle bolt before you installed the motor, its nearly impossible to fit once the motor is in place.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: BSA A10 to A70 A65 crank conversion [Re: gavin eisler] #757877
12/02/18 7:59 pm
12/02/18 7:59 pm
Joined: Aug 2013
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England
Servodyne Online content OP
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I know. It's a bitch if you forget it. A mate of mine forgot it on his 72 Lightning and gave the problem to his 12 year old son after he had put the pipes and carbs on. Poor lad tried for hours trying to get it in. lol

You did say it's nearly impossible??


1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando
1961 Norton 99
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757879
12/02/18 8:06 pm
12/02/18 8:06 pm
Joined: Aug 2001
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argyll. scotland, uk
gavin eisler Offline
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I have made this mistake in the past, I think I was able to finagle the rear plate into place with the puzzle bolt by removing the lower motor mount, leaving in the front mount and lifting the rear a bit, I remember succeeding without having to completely lift out the motor but it wasnt easy , paint got scratched and the air was blue for days,

Last edited by gavin eisler; 12/02/18 8:14 pm.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: BSA A10 to A70 A65 crank conversion [Re: Allan Gill] #757898
12/02/18 10:29 pm
12/02/18 10:29 pm
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NickL Offline
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Originally Posted by Allan Gill
Nick, what’s your view of fitting a triumph style oil filter in the bottom of the frame so that the oil is filtered before hand instead of after. Easy enough to convert and I should think the head pressure/weight of the oil is enough to stop the pump starving of oil?

LP Williams triumph oil filter


I don't really like filters in series with the input of a gear pump as they have little suction power. A full flow filter on the return ensures the tank is clean unless
you fill it with iron filings or suchlike.

As for holding more pressure, unless you have the thrusts sealed better or as well as the main bearing, they will pass the oil with little more resistance than
the open bush, but it's better than standard a65. Modern oil makes no difference at all. the thrust face on that side takes next to no load, the trust is toward
the pump side, there is no need for a bronze thrust face, Hardened steel against ally is a good combination.
Shame your leaving it that horrible dove gray colour.


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757904
12/02/18 11:32 pm
12/02/18 11:32 pm
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DMadigan Offline
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Thr thrust washer on the outside does not need to be as large in diameter as what he used since the radial thickness of the bearing is usable thrust surface. That also eliminates the problem of the washer interfering with the pump mounting.
Since, as you say, the thrust is mainly toward the timing side the washer could be thinner also. I would have to look closer at all the parts but it may be possible to not recess the case at all.
The other possibility is to use a roller guide ring on the drive side so the float is controlled there.

Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757910
12/03/18 12:01 am
12/03/18 12:01 am
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New Jersey USA
Tridentman Offline

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On the equivalent Triumph set up there is no need for the oil pump to suck.
Because the oil flow rate is so small the head of the oil in the "tank" provides positive pressure at the pump inlet.
Not sure of the oil flow rate on an A65---does anyone know?
If it is similar to a Triumph twin then the logic as above would apply.
HTH

Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757912
12/03/18 12:03 am
12/03/18 12:03 am
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NickL Offline
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The cases already have that large aperture machined if they are genuine a70 type.
The lined steel housed bush used by the a70 is just a narrower version of the a65 bearing so
using that as a thrust face is not ideal, i don't much like the idea of carving up the oil pump
to allow the washer to clear though, i'd rather recess the washer or as you say, use a thinner one.
The one Steve Wilson did used a one piece bronze bush so it has a suitable face for a thrust
similar to to the one i did, the bronze face is continued out a couple of mill by the ally case,
The washer i used was 2.8mm thick and 50mm diameter sitting about 5 thou below the surface
In all honesty, i think any of these setups will be fine for what they are.
Unless racing or similar the standard setup is good for the expected rebuild life of the engine, probably more.


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: BSA A10 to A70 A65 crank conversion [Re: Tridentman] #757913
12/03/18 12:07 am
12/03/18 12:07 am
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NickL Offline
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Originally Posted by Tridentman
On the equivalent Triumph set up there is no need for the oil pump to suck.
Because the oil flow rate is so small the head of the oil in the "tank" provides positive pressure at the pump inlet.
Not sure of the oil flow rate on an A65---does anyone know?
If it is similar to a Triumph twin then the logic as above would apply.
HTH


It would mean that the pump would have to be primed each time the filter is changed though.
Any cavitation would be a problem unlike a piston type pump.
Plus if allowed to block, it's doubtful the a65 pump could pull oil past the bypass in the filter if there is one.
I tend to like things a little more idiot proof and it's so easy to fit/change a return line filter plus i can't see
any real advantage.

Last edited by NickL; 12/03/18 12:19 am.

No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757923
12/03/18 3:14 am
12/03/18 3:14 am
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New Jersey USA
Tridentman Offline

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The filter element normally used on Triumphs is the B25 unit---it has no bypass.
Agreed---if it blocks you have a problem---if you don't change the filter element at sensible intervals you shouldn't put a filter on in the first place.
Having said that reasonable filter change frequencies means that blockage should not be a problem.
The advantage in my book is that you are filtering the oil immediately prior to it going into the pump whereas with a return filter you are filtering the oil going onto the tank.
Of course there is no reason why you couldn't filter in both locations---we always say that there are two oil pumps with separate circuits.
BTW on the Triumphs several thousand of the Charlie filters have been sold in UK and more overseas so the basic concept is IMHO well proven.
Installing it is straight forward on 1973 on Triumphs but the 71/72 OIF frames need some piping mods.
I think we all agree that adding oil filtration using a proper filter element is one of the best mods to do on these bikes --I have put several on Triumphs with no problems.
Still looks original and no extra connections to potentially leak.
Just my two cents worth of course.

Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757948
12/03/18 11:37 am
12/03/18 11:37 am
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argyll. scotland, uk
gavin eisler Offline
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IMO a return line filter is better for two reasons, it provides a useful boost to the oil capacity and it is relatively easy to access and change. I considered fitting a Charlie type filter on my rebuild , but didnt in the end.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: BSA A10 to A70 A65 crank conversion [Re: Servodyne] #757953
12/03/18 1:01 pm
12/03/18 1:01 pm
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Rotherham - S. Yorkshire
Allan Gill Offline

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Rotherham - S. Yorkshire
If im not misteken there is a mod for the B50 where a filter replaces the strainer in the oil feed tube (front down tube) If "a" BSA had a charlie type filter in the feed line i could foresee the cavitation problem, the head pressure pushing the oil will be lessened by the pipe feeding the filter, but as the filter is submerged in the oil, oil can't sit above it and would soak through the filter fast than it will feed oil to the engine.

I do know of one case where it has been sucessfully done. Im not against fitting a filter on the return line, my 68' has this. However it does put a level of back pressure on the system also, but I think this is down to the 68 crank cases dumping oil to the sump, where I beleive post 68 cases dumped into the return feed line.

Anyway I think I've hyjacked this thread enough, appologies Servodyne.

... I still like the frame colour grin


beerchug
Re: BSA A10 to A70 A65 crank conversion [Re: NickL] #757991
12/03/18 7:27 pm
12/03/18 7:27 pm
Joined: Aug 2013
Posts: 25
England
Servodyne Online content OP
BritBike Forum member
Servodyne  Online Content OP
BritBike Forum member

Joined: Aug 2013
Posts: 25
England
Originally Posted by NickL
i don't much like the idea of carving up the oil pump
to allow the washer to clear though, i'd rather recess the washer or as you say, use a thinner one.


The alteration to the oil pump amounted to a few thou being removed from material at the edge of the hole on it's forward foot. I must admit that it was far from ideal, but a thinner thrust washer wouldn't have given me the protrusion over the edge of the bearing sleeve to ensure sufficient clamping when the crank pinion and worm nut were installed. A recessed washer would have been a more elegant solution but I did think if there was any wear on the thrust washer in the future I could just reverse it.
This problem wouldn't occur with a standard A70 crank as the ID of the washer is the same diameter as the pinon and therefore would be firmly clamp while being slightly thinner.

Last edited by Servodyne; 12/03/18 7:29 pm.

1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando
1961 Norton 99
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