Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board T140 Drive spline wear.

Hi All,

I have excessive wear on the drive splines of the crankshaft of my T140v. Really I blame my complacency and laziness for not catching this sooner. The noise was always there (not so bad) when I first got the bike started after picking her up as a non runner about 11 years ago, and also I found some type of Loctite product in the end of the splines on disassembly. I had picked it as transmission, and probably because I would only notice it at low R.P.M, I would “get around to fixing that one day...”.
So the noise has all of a sudden got worse after a couple of recent high speed rides. After discovering where it was coming from, and I could be wrong, but it feels like I can turn the drive sprocket back and forth about 1/8th of an inch. It’s enough to replicate the knocking I have been hearing at idle anyway.
A couple of people have suggested the only way to repair it is a new crank... And I guess the bottom line is for peace of mind they’re right. I should add that the sprocket itself also has wear in the spline also, so it’s a sum of both parts causing the noise. I found a couple of used sprockets in my parts pile, one had the equal amount of rocking and the second had less. The machinist in me wonders if the splines on the crank can be successfully welded, indexed and re machined. Though I know there is special welders for crankshafts and by the time I start paying others to work on it, a good second hand crank maybe be more economical(?). Plus the time involved...
Has anyone had this issue before and successfully come up with a solution to delay the inevitable engine strip, major repair or replace? I have been thinking of cutting pieces of feeler strips or getting some tiny diameter “blue rod” cutting it to length and somehow knocking it in each spline, I guess anything will be tedious. As a last, “the engine has to be stripped eventually anyways”, solution could the sprocket be tack welded in place? I cringe at this though, with thoughts of tacks breaking away etc... I have come across this repair on a couple of Japanese dirt bike gearbox sprockets but obviously broken welds would have been less disastrous in that situation.
Any ideas/advice appreciated!
Cheers
Adrian

I spun a rear wheel bearing on the 72. It enlarged the hole the bearing fit in quite a bit. A new wheel bearing and a feeler gauge cut to fit and tapped into the gap and then the leftover gap filled with red Loctite cured everything. It's been in there for years now. Hopefully I won't live long enough to have to fix it right. Maybe a new gear and some red Loctite? Remember when it was called Triumph Loctite???

I think that you need a new or known good as new sprocket to absolutely determine the amount of wear to the splines of your crankshaft.
Until then you are just guessing at the problem.
It is rare for these to be a problem, my pre-unit ~1957 3-piece crank still has a close fit with the sprocket.
I suppose wear can happen here if the rotor nut was left untightened for a long time, how would that not show up at an earlier stage?

I know in the "olden days" folk would bodge with anything they could find to fill the gaps at the rearward sides of the splines. I've heard of knitting needles, nails etc, being used.
Depends on what you find the crank spline wear to be with a new sprocket. It may be fine as far as is known at the moment.

If it turns out to be excessively worn on the splines, then I'd suggest it is either a replacement crank, have your splines repaired, or bodge it.
The choice then depends on your wallet, or lifetime of use of the bike.

I think this is quite a rare problem, but certainly one that is known to occur occasionally. There was a T140 crank on Ebay a couple of months ago with absolutely shocking wear to the splines - despite this it got several bids and sold to some poor sod for well over £100. I can't imagine an economic way of repairing 'properly', unless you happen to be an expert machininst with a very well equipped machine shop.

Bodging to get the last bit of life out if it might be worth a go though? If you could make some hard steel pieces to hammer into the gaps, with a good sprocket, who knows how long it might last? As long as the rotor nut is really tight and there are no gaps for the sprocket's splines to move in, it could last for years. If it doesn't, you haven't lost much as it had to come apart anyway.

Hi All,
Spline wear is common enough on BSA A10's where owners do not tighten the cush drive nut properly
I have had a couple repaired by SRM in Wales who weld up the wear and re machine back to original profile
A long way from Australia I know but there must be engineering companies there who would do the job for you

John

I have used Loctite 638 to fix this, on splines and bearing shafts. There's no downside to it, and amazingly it lasts forever. 638 is a bearing fit compound, and available at most Loctite stockists.
I suggest you try it, after all it's a quick fix and there's nothing to loose by trying.
You won't dare to believe it really works, but you'll be surprised.

SR

Me too! Loctite has worked wonders on splines and alternator rotors on my bikes.

I think it depends on the degree of wear. I'm thinking about the crank I saw on Ebay which had a good 1/16" of wear to the crankshaft splines - far too much for Loctite to take up (unless you're relying on the Loctite to glue the sprocket to the cranks regardless?)

There must be a degree of guidance for the sprocket, so it won't end up eccentric to the shaft, but in reality that rarely happens. 1/16" slop is a lot but not if the diametrical fit is like half that I think.
Anyway, I'd try, nothing to lose but some time and effort... and BIG savings when it works!

SR

Hey all,
thanks for all the replies! I have a great few ideas to consider...
The first thing to do is to get a new sprocket. I actually have a bottle of 638 at the moment, however agree that it will come down to the amount of clearance. I work away from home and now won’t get to try the new sprocket for a couple of weeks. If the engine was apart I would definitely go down the welding and machinist route. I am a machinist so would only cost me time, but that is the rub! Time... I have a photo of the splines and video of the amount of play. I would be happy to share them here, however they were taken on my iPhone and the attachment manager says that the format they are in is forbidden. If someone has the skills to change the format, and post them here for me I would appreciate it and happy to email them to you.
Cheers
Adrian

I discovered this on a T140D I owned back in 2012. New crank needed for me. In the end I sold the bike as was and bought a wee 5Ta with the money

OMG!!! as my grand-daughter would say!

Can you imagine the racket it would have made, for a loong time? Some people have no mechanical sympathy whatsoever.
Here's a Norton clutch center I found in a non-runner, can't have sounded very nice either. Look at the inner splines.

That puppy had just one more smokey burnout left in it.
Cheers,
Bill

the crank spline probably takes more hits
as the clutch cush Drive ... loses its cush ... once there's an air gap in the spline started.
it builds on itself ... a good reason to use a low strength Loctite , from new on a good spline .
the spline cant hammer on itself ... if it does not move .
... rebuild the cush while you're in the area

locktite 660 is good to fill up to 0.5mm ... but its a real bear to undo .
if you use it ... write /scribe ...660 on the sprocket as a reminder
to yourself ... because if it works ... it's probably going to take heat and a puller to remove the sprocket .

there are a number of High solid , metallic filled epoxies ... on the market that
"could work" with a medium amount of spline wear ... heavy equipment guys use them
in the field to help eliminate downtime and the cost of a welded up repair ( proper , expensive and time consuming )
call around to your local heavy equipment repair guys ...
locktite , devcon and who knows how many other brands ... sell some industrial epoxies that have potential .
i see some listed with some impressive compressive strengths .
.

Looks like someone needs to check primary chain alignment carefully. Triplex chains are not very forgiving in this regard.

I had a crank for a triple repaired by Cranktech in Melbourne...that was ages ago and its still going fine. They welded and recut the spline. Only issue is avoiding heat stress where the shaft meets the crank web. If you can't stop this you end up with a weak point and could snap the drive side off.

https://www.truelocal.com.au/business/cranktech/ferntree-gully

That's all I could find on them. But not many such businesses have a website.

This seems to be true, as I've seen in other applications than motorcycles. The more rows the less forgiving. Which is why I use an IWIS Big Pin duplex chain in my Trident and other bikes.
The Trident chain has 12500 km on it, so early days, but I haven't had to adjust it yet.
Apart from alignment issues, one can always wonder if the crank and gear shafts are parallell...