Britbike forum Forums Thread Like Summary - Triumph pre unit gearbox rebuild - some questions

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...







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

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.

Well I filed the lip off.

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

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

“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.

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!

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!

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.

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!

“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.

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!

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…

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

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.

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.

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.

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?

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.

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

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.