Yamaha TRX850 Enthusiasts Forum

Hi;
I hope you don't mind me asking what may appear to be a simple question, but I'm going to anyway!
I've just bought a TRX which has stripped some of the teeth from the timing chain drive cog on the end of the crankshaft.
Is it possible to replace this cog and re-use the crankshaft, or do I need to source a new crank? (or is it easier just to replace the complete engine?)
In either case, could anyone suggest a source of the part(s) needed please?
Thanks for any advice offered.

You cannot economically replace the timing gear. It is machined into the billet of the crank. All the othe gears are shrunk on, but not that one - it is the one that commonly fails.

I have a crank sat in my garage if you want one. Otherwise Yamaha can supply a crank for around £800.

There is a braker in France that specialises in TRX and TDM. He has a crank with rods on his website... http://www.gn-moto.com/boutique/product ... 14aedc964c but even that is £475.

Let me know if you're interested in the crank I have.

this has happened before ,,but i cant remember if anyone has had a go at having the old cog machined off , a new one made and welded back on ! i feel sure it must be possable ,,,is this phatt,s old bike that you now have ?

I can recommend the French guy, I bought a 2nd hand cylinder head. Speedy service, and in better shape and more parts included than I expected!

steve speed wrote:this has happened before ,,but i cant remember if anyone has had a go at having the old cog machined off , a new one made and welded back on ! i feel sure it must be possable ,,,is this phatt,s old bike that you now have ?

There's very little meat under the gear steve. not enough to machine off and weld to easily.

the French TRX group were looking at having a bunch repaired, as a one off repair was astronomical, but even for a number of cranks the price was still prohibitive.

what are the chances of it being blue and brought off phatvr6???

Thanks very much for the info guys, and the offer of a replacement crank.

There is indeed a serious chance it may have been bought from phat, just hope I can get it all back together and have some fun on it.

don't put the camshafts in 180 degrees out!

brockzila wrote:what are the chances of it being blue and brought off phatvr6???

every

with the right machinist, you would be able to cut it off on a lathe, get a new gear, heat it up, freeze your crank, shrink it on. Its possible to do, but, still.. risky.

2nd hand might be one of the only options.

you'd have to remove the oil pump drive gear first, then machine down the crank to get a gear on there. the gear is so shallow to the crank though the new gear would be dead thin.

as you say its a bit thin , but my idea would be to weld it on as well

Even if you could somehow machine the old gear off, make a new one to EXACTLY the same dimensions, how can you 100% guarantee that it would be aligned exactly so that when the chain runs around it AND the camshafts, that the timing would be spot on? Just getting the gear half a tooth out of alignment with the crank would cause you loads of hassle.

I know there is a little adjustment on the sprockets, i.e. bugger all, but that would have to be some serious retro engineering.

Take Youngys crank IMHO, save you a lot of grief!