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Hi folks,
I'm slowly bringing a pre unit 6T Thunderbird motor & 4 speed box (fitted to Triton) back to life and have stripped the gearbox to replace a worn main bearing and oil seal.
Now it's ready to go back together I'm finding a few things that don't match the workshop manuals & Haynes.

* The mainshaft oil seal is held in by what seems to be a separate disk with a lip, is this just an old style seal that has seperated from it's outer metal shell?
* Removing the mainbearing was easier than expected. It was a nice sliding push fit into the gearbox casing, the manuals say to heat the cases as the bearing should be tight interference fit. Is this a problem or have a I got an earlier design of 'box? There are no signs of the bearing spinning in the housing.
* The brass/broze bushing between high gear and the mainshaft is a nice sliding fit on the shaft and inside the gear. Should this be a tight fit inside the high gear?

The gearbox casing is stamped 74274 and the end casing is marked 1955 if that helps...

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

Any advice or suggestion before I start putting things back together?
The plan is to get the bike working for the summer to shake problems into the open ready for a major rebuild of parts that need attention over the winter, so the target for now is "make it work".

Many thanks cool

Last edited by Nomad6T; 07/23/21 2:37 pm.

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I've just done this recently.
This was helpful.
Timing the quadrant was the only difficult bit.
I did several dry runs, before I put sealant on the cases, so when I did it for real , I had it all figured out, and didn't smear sealant every where.

https://hermit.cc/tmc/technote/gearbox/index_cam_quad/index.htm

There's also this.

http://americantriumph.com/holiday-...Q9KrEox5R1r5zQjTRBbQ3jxjfeC-VSI-Zjl1iHPM


1969 Royal Enfield Interceptor
1979 Suzuki GS1000S
1982 Suzuki Katana 1100
1996 Buell S2T Thunderbolt
1997 Harley Ultra Classic

Triton project, mainly boxes of stuff.
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Thanks for the links - I'd seen a couple of good pages on the Hemit site before, the AmericanTriumph was new and helpful.
beerchug

Last edited by Nomad6T; 07/23/21 2:35 pm.

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Regarding your questions in your first post:

The high gear bearing should be a firm interference fit in the housing.
It should require heating the case to remove/install.
So the housing may be oversize (most likely) or the bearing is undersize, or a bit of both.

Once the bearing is in place, there should then be a circlip which fits in a groove in the housing. This retains the bearing axially in its recess.

The oil seal is then pressed into the housing (open side inwards) until it is stopped by the circlip.
The ~half a dozen seals I’ve fitted over 40-odd years have been rubber-coated on the outside, and press firmly into the housing without any additional “collar”.

The long sleeve gear bush should be tight inside the sleeve (not free at all). The bearing surface is the inside of the bush, on the mainshaft.
If the bush is loose inside the sleeve gear, there is nothing to hold it axially, so it is free to migrate in either direction and make unintended contact at either end.
This bush is difficult to DIY replace, and will often need some reaming afterwards, as it tends to tighten with the long pressing, as well as the compression of the interference fit.

Your gearbox is a little earlier than mine (pre-slickshift style as opposed to slickshift style) but AFAIK the only differences were in the timing side inner and outer covers.
These differences were due to relocation of the clutch lever, and had nothing to do with the above issues.
The only other difference was the later use of needle bearings (rather than your bushes) for the layshaft, which again has nothing to do with the above issues.

Purely speculating, I wonder if the gearbox may have been run at some point with vastly inadequate oil level, causing the sleeve gear bush to tighten on the mainshaft, and so spin in the sleeve. Possibly that situation could also have seized and spun the main bearing. I know you say there is no sign of spinning, but without precise measuring it may be less than obvious to the eye.

Alternatively, a PO may have been creative (AKA destructive)?

Best of.

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I'm not sure what you have there! The bearing sould be an interference fit in the casing, but it should not be a sealed bearing like the ones shown either. The bearing is retained in the housing by a circlip, then the seal pushes in outboard of that, with the inner diameter of the seal mating with the high gear O/D.
The bronze bush should indeed be a press fit in the high gear.
You can use Loctite bearing fit on a loose bearing, I personally use the correct RHP open bearings, as sold by the better dealers, but the bearings are likely the same size anyway, and you can always hook out the built-in seal. A new bronze bush will be a pess fit in the high gear, but you will highly likely have to ream the bush once fitted to be a nice sliding fit on the mainshaft.
HTH

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+1 to Tinker except:

“then the seal pushes in outboard of that, with the inner diameter of the seal mating with the high gear O/D.”

The ID of the seal fits around the OD of the sprocket boss.

I agree that sealed bearings are not suitable for this application. They would normally be used for situations where lubricant isn’t freely available otherwise, eg wheel bearings. There should be plenty of oil splashing about in the gearbox, assuming the level at least reaches the layshaft gears.
Sealed bearings would typically be used in lower rpm situations than that of a gearbox mainshaft (which runs up to ~half crankshaft rpm. Once the original lubricant has escaped (which it will inevitably do) the bearings will be shielded from adequate splash.

I suspect a PO has had problems with oil leakage from the sprocket end of the gearbox, and has tried a sealed bearing. However, oil will still leak around the loose fit of the bearing in its housing, though it should still be held by the oil seal on the sprocket boss (there can be minor leakage along the spline gaps between sprocket and high gear – sealant?).

I’d suggest you either do some precise measurements of ID and OD’s or get a new bearing and seal and see how they fit.
Does that extra collar go round the seal? If so, I suspect the housing has been modified. Does a circlip groove still exist in the housing?

Best of.

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Things are now clearer, many thanks :
The main bearing / housing fit isn't as tight as it should be (I'll use bearing fit during the rebuild)
I ordered a new sealed-type main bearing as I thought that was correct, odd that the original bearing is also sealed type. Hooking out the seals is an option.
The bushing should be a tight fit in the high gear but isn't, I'll look at my options (use bearing fit during the rebuild ?)

Other info:
The circlip holding the main bearing in the housing looks fine, I ordered a new one so I'll fit that as a precaution.
I'm in Southern Europe so machining parts isn't an option, and getting new parts isn't practical (my last UK delivery took over 2 months)
Taking the high gear and mainshaft in handluggage on my next trip to the UK might be an option to get a new bushing fitted...
The history / PO of the bike is all unknown so I can't help with the history of use / abuse.


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“I ordered a new sealed-type main bearing as I thought that was correct, odd that the original bearing is also sealed type.”

Far as I know, sealed bearings didn’t exist in the 1950’s. Even if they did, they weren’t used in this application. That you have one (or two) installed is likely some idea a PO had in more recent decades to attempt to solve a problem, is my guess.
More than likely was an oil leakage problem.

A Loctite variety may deal with the slack bearing (as long as its still a good fit).
See what a new seal fits like, I still wonder about that extra collar.

Definitely take the seal out of the bearing on the inside of the main bearing, and I’d suggest both of the timing side bearing.

I’ve been into Tritons since 1975, so will be following your trials and tribulations!

Best of.

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Back in the 60s in the UK when Loctite was not yet around and we didnt have two halfpennies to rub together I remember on one occasuiobn we had a similar loose bearing in the case.
We carefully wound the outside of the bearing wone wind with the thinnest shim stock we could find and gently tapped the bearing c/w shim into the case .
It worked and was working OK at least fior a couple of years when the bike was sold on.
A bodge?--yes---but it was either that or no bike.
Sometimes needs must.

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Hi TM,

I expect that was easier described than done? Keeping the shim with the bearing would be no simple task, and you can’t bash on the shim, unless it is really quite thick (say 5+ thou). What was your technique (if you can remember that far back!)?

Nomad, when you get the new bearing and seal, just see how well they fit. If the bearing slip fits without any slack, loctite may do the job. Any looser than a couple of thou and I don’t rate your chances very highly.

Then you may need to listen to TM’s shim description, if you wish to avoid serious engineering work. Ideally the bearing cavity would be sleeved or built up, then re-machined.

Is Portugal so entirely lacking in engineering facilities? I wouldn’t have thought so, though the engineering may not be for old British bikes. I’ve worked at Azeitao for Jose Maria da Fonseca, installing equipment, and they could cope with every issue that cropped up. I’d be surprised if there aren’t facilities in Portugal to do this sort of work.

The sleeve gear bush being loose in the sleeve is the first time I’ve EVER heard of this. It just doesn’t happen. I suspect a PO tried doing it his own way (possibly found it difficult to press a new bush in without it compressing), so made it a slip-fit in the high gear, just maybe?

Nowt so strange as folk!

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Originally Posted by Tridentman
Back in the 60s in the UK when Loctite was not yet around and we didnt have two halfpennies to rub together I remember on one occasuiobn we had a similar loose bearing in the case.
We carefully wound the outside of the bearing wone wind with the thinnest shim stock we could find and gently tapped the bearing c/w shim into the case .
It worked and was working OK at least fior a couple of years when the bike was sold on.
A bodge?--yes---but it was either that or no bike.
Sometimes needs must.


I heard of shellac being used instead of Loctite. Probably an "Arfur Daley" type bodge, like putting saw dust in a whining gearbox.

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Apologies for the spelling in my last post---trying to hurry!
Koan---it was a long time ago but if I remember correctly we made the shim stock wider than the bearing outer and put the shim into the case bore first then tapped the bearing outer in.
The shim was a sort of cone shape guiding the bearing outer into the bore.
When fully home cut off the surplus shim stock.
HTH

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Quote
I expect that was easier described than done? Keeping the shim with the bearing would be no simple task

When I have used this technique I have fitted the shim 1/2 way into the housing followed by the bearing being centred in the shim before then tapping the bearing home, the bearing drags the shim in enough so its fully seated as long as the shim is not too thick.

On a loose crank main bearing loctite to restore inference fit does not last more than 1000 miles, the heat cycles and the 2 differing expansion rates of the steel and aluminium break the bond and the loctite fails. On a pre unit gearbox with lower temps loctite may work but for how long.

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Apologies, I was on holiday and enjoying FAR too much wine.
Any engineering place will have adjustable reamers (no worry about imperial/metric), I get my fancier work done by a toolmaking company, they make and modify plactic moulding tools. There are two of these companies near even where I live in rural Buckinghamshire.
If you really get stuck, send the high gear to me and I'll do it for you!

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Thanks to everyone for the advice - and TinkerToo for the very kind offer of helping out if needed. It's all appreciated.

I now know more than I did.

PO was a hamfisted bodger (or everyday rider of the time). The mainshaft / mainbearing bush is a sliding fit into the high gear when it should be tight, and the outside has been peened in the past to take up the slack.
This has allowed the bushing to slide out of place and it now has a significant wear ring on the outside (note at the tip of the screwdriver)
[Linked Image from i.postimg.cc]

We've just had a powercut in the village. With little else to do I hit the case with a brass wire brush in a battery drill, lubrication (for me) was with local beers.
Results are a big improvement.
[Linked Image from i.postimg.cc]

It's progress. If I had easy access to parts and machines I'd renew the bushing now, as it is I think I'll put it together and maybe take the parts back to the UK with me later in the year for machining.

TinkerToo & others, posting from Europe to UK is ok, return post from UK to anywhere in Europe is now a nighmare as it's classed as "Importing into EU" - so needs customs declarations & this leads to all kinds of problems. Best avoided if at all possible. frown

Last edited by Nomad6T; 07/24/21 4:29 pm.

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TinkerToo - just for info I tried to send a message but the system says you're over you limit.

A mate is planning to drive from UK to Portugal in October and will be able to bring parts for me without shipping them through customs.
I'm hoping I can get the bike on the road for a couple of shakedown runs before then so I can give him a list of parts I need.
If I make a trip back to the UK I have access to a couple of good machine shops, if not I might take you up on your very kind offer.

Thanks again everyone beerchug


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Do you have access to the RAT forum? I post there under Mick Barratt (my name!), as far as I know there's a pretty liberal PM on there.
Cheers,
Mick.

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Today has been "fun" facepalm

The main bearing was a sliding push fit into the casings, no need for shims so I've used bearing locktite, this should be fine for a few short test runs, maybe longer.
The high gear/mainshaft bushing has been refitted using same bearing fit, it's not ideal but again - it should be ok for test runs.
The mainshaft where the highgear runs has slight but definite wear, it's not ideal but ...

I hooked the oillseals out of the new bearing, measured old & new parts and they seemed to match apart from the oilseal so I fitted the bearing - circlip - oilseal. All went well so I had a beer to celebrate.
The highgear fitted the bearing fine but when I tried to fit the drivecog and couldn't get it into the oilseal.

Rechecking everything shows the centrebore of the final drive sprocket is too big, it's engaging the teeth on the driveshaft but only slightly, it's also wider so the final drive nut is flush with the end of the mainshaft.
The oversized sprocket explains why the original oilseal was non-standard, the new oilseal is about 1/4" to small to fit this sprocket.
As a temporary measure I've removed the oilseal and refitted the "sealed highgear bearing" cover to the outer race for testing.

[Linked Image from i.postimg.cc]

I've stopped there for today but noticed when I did a trial fit with the other endcasing the mainshaft seems to have too much endfloat (3/16" ?) so I supect there's a spacer missing somewhere ...

It clearly needs a new final drive sprocket but today just confirms I need a couple of test runs as I can't wait 2 months for a UK delivery every time I find a new problem.
facepalm


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The mainshaft is located positively in the inner end cover by the end nut tightening onto the lockwasher, kickstart ratchet and kickstart pinion sleeve in that order - no endfloat. That sprocket obviously does not belong, and would be deadly!

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“The plan is to get the bike working for the summer to shake problems into the open ready for a major rebuild of parts that need attention over the winter, so the target for now is "make it work".”

“PO was a hamfisted bodger…” I’m tempted to agree with this.

That sprocket is a disaster waiting to happen, as Tinker says. It has such little purchase on the splines that it is almost certain to slip under drive. Even if the high gear/sleeve is serviceable now, it almost certainly won’t be after that has happened.

Whether the PO installed that sprocket because it was all he could find, or whether he wanted higher gearing (pre-unit gearbox sprockets were only ever 18T, though other tooth counts are available now), it was a bad move.

The chances of keeping oil in the box with that sprocket/seal arrangement are slim.

Also the bush that you have loctited in should be flush with inner end of the high gear, and should protrude from the clutch end by perhaps 3/8” (at a guess). It nearly reaches the clutch hub, passing through the sliding oil seal of the inner chaincase. It is the wear of that bush against the sliding seal that you pointed to in a recent post Though the wear is usually a narrow ring corresponding to the thickness of the sliding seal, whereas yours is much broader due to the mobility of the bush in the sleeve gear.
It may be that your bush has been ground shorter than it should be by having made contact with the mainshaft second gear.

I doubt the usefulness of running this gearbox as it is.
If the same PO has done anything to the engine, that would only add to my doubts.
You may end up with scrap, or worse put yourself at risk.

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Hi Koan,

I agree totally about the fit of the sprocket and the risk of damaging the highgear / sleeve but thanks for the warning. I'm trying to work out how to get everything I need on my next UK shipment (when my mate visits in October?). A new sprocket & sleeve bush are top of the list but I'd like to see if there's any other big problems lurking before then so I can get the parts I need at the same time.

The bush I've loctited is a lot shorter than you expect but at least the wear on it is now explained - thanks. It's slightly shorter than the width of the highgear so is slightly recessed at both ends, not protuding at all.

I stripped the engine down when I got the bike & cleaned the sludge tube. Most other parts were ok after replacing the big end bearings. As predicted, the engine internals had a few surprises but I'm happy with it for now.

Keep the suggestions coming everyone, this should be a simple machine to get back on the road - I just need to work out the easiest way to do it beerchug


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Hi Nomad,
While these old bikes are simpler in design than modern stuff, don’t be tempted to under-estimate the importance of careful assembly with good quality well-toleranced components.
While they can be made to run by throwing worn bits together, the result is likely to be disappointing and short-lived.

Considering what we’ve seen thus far, my inclination would be to check everything in detail and to fully understand exactly what you have.

You’ve cleaned the sludge tube. That suggests it’s a later crank, as the original crank would have been 3-piece, which would be dismantled (6 nuts and bolts) to clean the cavity (not a tube). Is that what you have?

With a Triton, you also have the engine/gearbox not in its original frame. Does it have a Norton rear wheel/brake drum? A wideline would have a 1/4 “ sprocket here. The correct Triumph gearbox sprocket will be 3/8 “ wide.
A 3/8 “ drum/sprocket is available for later 60’s Nortons, but will also need the later 3 Fasteners (different thread).

Does the bike still have magneto and dynamo? If so, they are unknown quantities, and would be a good reason for being able to run the engine, but not necessarily ride the bike. These can be very expensive to deal with.

What carburettor does it have? Is it an iron or alloy head? Did you notice what cams it has while you were in there? It can make a difference to cam-wheel timing and valve clearance.

And we haven’t yet touched on cycle parts or most of the electrical system.

A Triton is more work than a standard Triumph, don’t be fooled.

Best of.

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Ignore some of my previous post, I've just read your other thread! Apos.

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Hi Koan, the pointers are all appreciated, some answers :

The crank was cleaned by my machine shop many years ago so I didn't see it apart, from memory it was accessed via a circular cap (3/4" for a guess) in the side of the crank. It has an alternator fitted so is a later crank?
The rolling chassis is all original Norton, I hadn't thought of the mismatch between rear wheel & gearbox - good point. That could explain the odd gearbox sprocket. The rear drum is in good condition so I wasn't planning to change it but ...

The bike is running with :
a distributor but I have 3 spare magnetos here (1 was good - not tested recently, others are complete but untested)
I have 3 monoblock carbs here, the best condition is slightly oversized for the bike (276 ?) but is ok for testing.
There's also a SU carb & manifold stored in the UK that might eventually end up being used.
It has an iron head, I think cams are 3134, I set with standard gaps and timing (6T ?) and it's happy to start and run around the yard.
Electrics - I recently rewired totally with a DIY harness and I have confidence in that side for testing (the charging circuit hasn't been checked yet)

I have a rebuild thread with more info (I though asking about the gearbox problems on the dedicated Triumph section made sense hence the separate thread)
https://www.britbike.com/forums/ubb...ine-650-thunderbird-awakening#Post831335
beerchug

Last edited by Nomad6T; 07/25/21 9:17 pm.

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A couple of comments about the engine, having had a bit of a look at the other thread. Count the fins on the head, the 6T had (mostly) 4 fins, while the very similar iron T110 had 5 fins. I believe the very late Iron 6T head also had 5 fins, but the inlet and exhaust valves were the same size on this oddity - I've never seen one. Either way, as long as the bore of the inlet manifold matches the carb bore, the 389 carb you have would be fine, particularly if you have E3134 cams. Which leads me to valve clearances, the E3134 cams need 0.002" clearance on the inlet and 0.004" exhaust, but the 6T ramp cams are 0.010" inlet and exhaust, so you really do need to know what cams are in there!

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Hi Koan, I think I've finally found some good news.

The rear wheel brake drum / sprocket measures 3/8" wide (so does the "scrap" gearbox sprocket) and has the correct chain,so the rear wheel is ok as it is.
It looks like i just need a standard 3/8" Triumph gearbox sprocket to fix the final drive setup - if so, I'm happy.

To double-check, it's wider than the primary drive which I measured as 1/4"

In other news, I've just booked a UK flight for mid-September so I'll be able to collect the parts I need when I'm in the UK. I still need to work out what I need...

Never a dull day
beerchug

Last edited by Nomad6T; 07/26/21 11:41 am.

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Hi Nomad,

TriSupply is a good quality supplier (Oliver Barnes the proprietor really knows his stuff and knows these bikes inside out) but can be on the expensive side for run of the mill bits.

I’ve mainly used TMS Nottingham for most parts over the last 20 years, as most of the suppliers I used in the 80’s and 90’s have gone.
http://www.tms-motorcycles.co.uk/

Only an 18T gearbox sprocket was originally available for pre-units, as gearing changes were done with the engine sprocket.
I note that “disaster” sprocket of yours is 19T. As I said previously, we can’t know if that was just any old sprocket he had on hand to try to bodge-fit, or whether he wanted to gear it up a little on the cheap.

TMS list engine sprockets from 19T-24T.
The standard for a 6T would have been 22T (the more powerful and rev-willing TR6 and T120 had 21T).
How many teeth are on your engine sprocket? If it is in good condition you may wish to re-use it.

So when you buy a new gearbox sprocket (IMHO you must) it would be worth considering the overall gearing from crank to rear wheel, while keeping in mind factors such as:
-the bike is significantly lighter than the original Triumph
-the engine may have more power than original
-the kind of riding you expect to be doing (short twisties needing acceleration, fast roads/motorways etc)
-solo or with pillion

The original sprockets for a 6T would have been 22 engine X 43 clutch, then 18 gearbox X 43 wheel (with 3.50x18 tyre).
What is your rear tyre? It would be 3.50x19 on the original Norton rear wheel.
I think you can imagine the considerations involved.
Of course this only really matters if you hope to enjoy the bike to the max when its fully sorted, if just selling it on then less to concentrate on.

It is good you’ve already got the later rear 3/8 “ sprocket/brake drum (from the late 60s). I only found out about that when I bought my first triton (a bag of sxxt) when I was 17, it had a gearbox sprocket slimmed to ¼ “ to match the wheel sprocket, they wore out in short order. I didn’t know of such subtleties in 1977, so when I bought a new gearbox and rear wheel sprocket at considerable expense, I discovered the mis-match. Gotta get a sprocket from a late Atlas, and also the nuts to suit.

You’ve got a Norton front end, except for the brake plate. My guess is that’s from a late 60s Triumph (or BSA). They first introduced them in 1968 (I think) and it was with the problematic cable routing that you have. The following year it was modified to bring the cable in line with the fork.
There will be people here with expertise in this, I believe different components can be used to obviate the issue.

Moving on, I have no idea what’s going on with the clutch nuts and springs. They are not right. Its not surprising that they are leaving marks on the chaincase, they protrude far beyond the pressure plate. Get the right bits I‘d suggest.

Good to see the alternator is of the later encapsulated variety. Is it 2 or 3 wire? No simple way to know if the rotor magnetism is still strong enough for practical use until you run the engine.
What electrical bits were fitted, as in switches, bulbs, anything?

I’m not too excited by a distributor, but as its working that’s a good thing (better than 3 unknown magnetos).
There are other options in this area depending on where you wish to go with this project.

The old photo is pretty, but there’s nothing Manx about it. I had exactly the same tank for years, before ethanol destroyed it. I now have a vaguely similar shape alloy tank.
That is what I requested when I had it made.

I think the Manx look is pretty, but it is so ubiquitous that I find it a bit monotonous, like a uniform. That is why I posted years ago “Is the Triton still a special” because most builders were making bikes in a similar mould. I thought a special was supposed to be individual.
You could line up dozens of tritons along Brighton esplanade and hardly tell one from another. That is not individualism to me, its following a recipe.

Only my silly thoughts…

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Originally Posted by koan58
Only an 18T gearbox sprocket was originally available for pre-units, as gearing changes were done with the engine sprocket.
I note that “disaster” sprocket of yours is 19T. As I said previously, we can’t know if that was just any old sprocket he had on hand to try to bodge-fit, or whether he wanted to gear it up a little on the cheap.

TMS list engine sprockets from 19T-24T.
The standard for a 6T would have been 22T (the more powerful and rev-willing TR6 and T120 had 21T).
How many teeth are on your engine sprocket? If it is in good condition you may wish to re-use it.

So when you buy a new gearbox sprocket (IMHO you must) it would be worth considering the overall gearing from crank to rear wheel, while keeping in mind factors such as:
-the bike is significantly lighter than the original Triumph
-the engine may have more power than original
-the kind of riding you expect to be doing (short twisties needing acceleration, fast roads/motorways etc)
-solo or with pillion

The original sprockets for a 6T would have been 22 engine X 43 clutch, then 18 gearbox X 43 wheel (with 3.50x18 tyre).
What is your rear tyre? It would be 3.50x19 on the original Norton rear wheel.
I think you can imagine the considerations involved.
Of course this only really matters if you hope to enjoy the bike to the max when its fully sorted, if just selling it on then less to concentrate on.

Hi Koan / everyone. Apologies for the slow reply I have a flight back to the UK booked for 2 weeks time and I've been trying to get lots of thing arranged.

Gearing now on the bike is 22 engine / 43 clutch, 19 gearbox / 42 rear wheel (if I counted the teeth right), rear tyre is 4.10/19 but needs to be changed due to age. All sprockets have good teeth so I'll only be changing the "disaster waiting to happen" one.
The bike has been a long term project so the plan is to get it on the road and fix things later once I've ridden it for a few months, I'm expecting most riding to be steady solo runs on smaller roads, possibly some distances on motorways. Gearing for relaxed cruising wiould be fine, no need for dragster gearing.

I suppose the question would be - what size gearbox sprocket (19T-24T) should I buy as a replacement ?

Thanks again


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Hi Nomad,
Would be worth double-checking your rear wheel sprocket, the ones I've used have all had 43 teeth.

The 19-24T options are for the ENGINE sprocket.

TMS list 18-21T options for P/U GEARBOX sprocket.

http://www.tms-motorcycles.co.uk/store/products/list.asp?cat_id=173&order_by=name

I would suggest 18 or 19T

Cheers

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Sorry, I was a little short of time this morning to fully go into the matter.

The original sprockets for a 6T would have been 22 engine X 43 clutch, then 18 gearbox X 43 wheel (with 3.50x18 tyre).

Assuming your rear wheel sprocket does turn out to be 43T, then using an 18T gearbox sprocket will leave all the sprocket ratios as standard for a P/U 6T.

The only difference will be the 19” Norton rear wheel, increasing the gearing by ~5.5% over the 6T (the 4.10 won’t be significantly different in outside circumference to a 3.50 – different profiles).
That is where you will be with a standard 18T P/U gearbox sprocket, possibly a reasonable starting point with a 6T Triton.

Going from the standard 18T gearbox sprocket to a 19T is another ~5.5% increase, so a total of ~11% above standard 6T gearing. That is quite a leg up.

If it’s only to be used solo, the lighter weight of the bike (compared to the original 6T) might make that work, but most builders would use components from the T120 (or maybe TR6 and other variants) to increase power.
Then you could possibly go to even higher gearing.

If it is a fairly standard iron head 6T, you could have a good riding experience, perhaps without ultimate performance, with what you have, on fairly standard gearing.

19T gearbox sprocket is my suggestion, but if it turns out TMS can’t supply it, don’t worry. If you find that you’re desperate to gear it up after you’ve ridden it, the engine sprocket options (up to 24T) may be available.

The only reason I got into this subject was that in the early 80’s I installed unit duplex parts into my P/U. This meant the primary ratio was 2:1 (no options).
I had already gone to 18” wheels. I found the gearing too short for comfort.
No alternative gearbox sprockets were available back then, so I had a 21T made by Supasprox. It has worked fine on a light Triton with a mildly hopped T120 engine ever since.

So this example is, from front to back, 29 X 58, 21 X 43, with an 18” 4.10 tyre. So it is significantly taller geared than a standard Triumph 6T (even more than a standard T120), but it is ~50lbs lighter than those, and pulls it well.

Of course, raising the gearing increases the gaps between the gears. This has trivial impact on my road-riding experience, but could be important if you were racing. MickB Tinkereretoo may be one to talk to on this subject, he fits 5-speeds into pre-unit boxes. I've been tempted but never quite gone that route.

Hope this is of some help.

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HI Koan, no need for apologies - I really appreciate your help as this is an unkown area for me,

I rechecked the rear wheel and recounted the teeth, I still get 42 (not the 43 you expected).
The origins of the sprocket are unknown but it's been on the bike since at least the late 70s ...

You have given me plenty of info to make a start. I'll keep everyone updated when I get back from the UK.
beerchug


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Well 42 teeth is unusual to me! See:
https://www.rgmnorton.co.uk/dept/sprockets_d0178.htm

The 2 5/8 X 3/8 sprocket drums are both 43T.

It is a Norton wheel?

42T will raise the gearing a little more beyond my expected 43T, by about ~2.4%.

Add this to the impact of the 19" rear wheel (as compared to the 6T's original 18" ~5.5%), then you're already looking at ~8% gearing raise using a standard 18T gearbox sprocket.

An extra tooth on the gearbox sprocket (to 19T) will add another ~5.5%, making ~13.5% total gearing raise over 6T standard.
That really is quite a lot, probably not something I'd entertain with a standard 6T engine. It might be appropriate with a 750 conversion and/or sportier head and cams.
I'm sure a good 6T will pull that high gearing, but acceleration and 2-up use will suffer, and you may find in some circumstances it will be faster in 3rd than top.

I would suggest sticking with a 18T gearbox sprocket for now, and feel how it goes.
When you come to fully recondition the bike, a change to a different sprocket will be a very minor part of the cost.
Don't forget that you don't necessarily need to change the gearbox sprocket. If using the original single chain primary, you can increase the engine sprocket up to 24T. Going from 22 to 23T here will be ~4.5% gearing raise.

Lots of options! Cheers.

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Having a trawl about, I do see that 42T brake drum sprockets were used for some late 60's models and Commando. I've learnt something.

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Things are moving, very slowly (I had a trip back to the UK recently and bought some bits while I was there, and brought the parts back with me in my suitcase..)
Rebuilding the gearbox with the new parts hasn't gone the way I hoped.

First, I cleaned the casings while the box was strippped, rebuilt the internals, reassembled the box, and when done refilled with oil - which prompty started leaking from the casing.
PO etc has shaped the casings using a file, I guess for extra clearance, and has *just* broken though in one spot. Short term I'll seal it with chemical metal if I can find any locally. I know people in the UK who can weld the casing but I need to get the casing to them. Not a disaster but it's very frustrating !

[Linked Image from i.postimg.cc]

I also ordered new clutch springs "5 plate, 4 speed pre-unit" from TriSupply who have been very good in the past. See photos - the original springs are the short narrow ones.
New springs extend a long way past the coverplate, is this right?
The plates and cover are a long way below the edge of the clutch basket.
Is this a sign that the whole setup is mismatched parts put together, maybe a 6 plate basket fitted with 5 plates or some similar bodge ?
I realised too late that the nuts holding the clutch springs need changing for standard ones ... will add them to my next parts order.

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

I'm assuming nothing. The bike came to me as a complete engine (out of the bike, wrong engine plates - possibly BSA), rolling chassis with gearbox fitted (not sure if had ever been used or if it was an incomplete conversion), missing chaincases which I bought later.

Last edited by Nomad6T; 01/23/22 4:34 pm.

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I just had a quick look at a spares manual (the '56 one), just to confirm what I was pretty sure of, and the only clutch with the 5 plain and 4 friction is the one on the 5T. All others used 6 plain and 5 friction and the cups should be 57-0998, which are longer. I actually machine off the flange at the back of the cush hub, which allows 6 plain and 6 friction as per the unit engines - the 7 plate conversion allows 7 and 7, but I'm using engines that I convert to 750 with more radical cams - a lot more power than you will have!
I don't have any of the 5T clutch bits, so can't measure, but this info should help.

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Is it time to mention the late Pete Russell’s recommendation again, to glue cork mat onto the 650 clutch basket and squeeze an extra plain plate in?


Amateur Loctite enthusiast.
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I’d forgotten about that, I just did a late T140, and that’s exactly what it had! You still have to machine off that lip, though.

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Well I filed the lip off.

Now that I own a quaint old lathe, I’d use that.


Amateur Loctite enthusiast.
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Originally Posted by Tridentman
Back in the 60s in the UK when Loctite was not yet around and we didnt have two halfpennies to rub together I remember on one occasuiobn we had a similar loose bearing in the case.
We carefully wound the outside of the bearing wone wind with the thinnest shim stock we could find and gently tapped the bearing c/w shim into the case .
It worked and was working OK at least fior a couple of years when the bike was sold on.
A bodge?--yes---but it was either that or no bike.
Sometimes needs must.


how have i missed this useful thread?

i have done the shim stock thing with trailer wheel bearings, when the correct-by-number new bearing was still too loose in the bore. it worked for a few thousand miles, then i swapped for heavier axles and cant tell what happened after to them


i'm old enough to remember when patriotism meant not trying to overthrow the government.
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Thanks everyone, I'm busy tomorrow but will look in daylight in the next few days and report back.

beerchug


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As someone who used to "get things going" at the expense of an imagined final build quality, I've found that it's a false economy. I had a "dry build" that got ridden for the better part of a decade, because stripping the bike and fixing all the niggles didn't sound that fun, so just didn't happen until it absolutely needed to happen. It was a waste of time, money and energy to not do it right from the start, and that's with no major breakdowns (or injuries!).

With a gearbox on a Triton, there is a lot of disassembly involved just to get that thing out of the frame. They do not come out easily. Much of the internal work on a gearbox can be done in the frame, but if you've got dodgy castings, you're MUCH better off to fix them permanently now and be done with it.

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