richty250e

Hi Neil, Did you clean out the fuel tank and carb float chamber? Possible you got some water in there if submerged for a while and as water is heavier than petrol it will sit in the bottom of the tank and float chamber until you drain it. Could be the impact dislodged some dirt and it's found it's way into the carb jets. I'd start by giving the tank and carb a good clean out and blow through with compressed air. Rich

Hi Kevin, Stork The TY250 has a helical primary gear set which will put an axial thrust on the crank main bearings during drive/overun same as the GG. The bearings appear to be the deep groove type so they are designed to cope with some axial thrust. I took all the measurements with a metric vernier caliper/depth gauge so it is all metric I'm afraid. The cases are vertically split and do not have a paper gasket fitted, they are just sealed with yamabond. I will recheck my measurements again over the weekend with better equipment and see what the verdict is.

Just had a chat with John Cane whilst ordering some frame parts and it seems that not all TY engines came with the shim and the ones he has built without one worked fine. So there we have it, if you have one in your engine put it back in when you rebuild. if there isn't one don't worry about it. Just goes to prove you can't always trust the manual/parts fiche and there's no substitute for hands on experience. Thanks all for the replies. Rich

Hi Alan, No - manual just says to "fit the shim". No description of how to calculate shim thickness needed etc. Thanks for the DT piston info. I need a +1.0 piston and genuine TY pistons are very very rare in that size with only cheap aftermarket kits (dubious quality) or Wiseco ($$$$) to choose from. I'll keep a look out for a genuine DT one now I know they will work with a little 'machining'. cheers Rich

Hi Tony, thanks for that tip about cycle-parts.com. They do have the shim listed for $4.99 but the minimum order is $75! Will have to wait until I need another expensive item to combine orders I think. In the meantime will try to contact feetupfun for his view. If your looking for a long term fix for that header there is a stainless steel one available now at Sammy Miller Products. cheers Rich

Thanks for that Stork, the differences between TY and DT parts are quite vague. Do you know if the DT piston works in the TY? Well I did a quick measure up of the crank and cases and it appears that there is about 1.5mm axial preload on the main bearings with no shim fitted. Sounds a lot but when you take into account the different thermal expansion of the aluminium alloy case and the steel crank then it would be less when it's at running temperature. The main bearings are C3 spec so have extra clearances when cold so that also figures into the amount of preload needed. One other thing that crossed my mind was the fact that the TY magneto rotor has the extra weight, so maybe the Yamaha boffins decided to increase the preload to control the extra crank whip on the TY motors. Still doesn't account for the change in the parts fiche diagram though!

Thanks for the reply Tony. It sounds like you have the same manual (TY250B by Cycleserv Publications) as me. The problem for me was that the left side case (as per the manual) is the magneto side, but in the parts fiche for the TY250B the shim is shown on the primary gear side. The fact that I didn't have any shim fitted at all doesn't help. I also looked at the DT250 parts fiche and that doesn't have any shim fitted. The shim appears to be a TY specific part and was never fitted on any model year of the DT. From what I can see the shim would control axial main bearing float/nip if fitted on the inside, and primary gear alignment with the clutch basket gear if fitted on the outside. From an engineering standpoint I would be surprised to see a shim fitted on the inside of the main bearing for three reasons:1, it would increase the stress on the crank. 2, the crank has a tight tolerance given for width during rebuild. 3, I've never come across any other crank that uses a shim in that position. The problem I have is that I write repair manuals for a living (on cars though) so I know that no one is infallible and this is an easy area to make a mistake about when it comes to writing the process down in a book, or even producing the parts fiche drawings. Maybe the only solution is to bolt the empty cases together and measure the width between the main bearing housings and compare that to the width of the crank with the main bearings fitted without a shim. I guess if the difference is in the range of the shim sizes 0.3 - 0.5mm then we will have a definitive answer. This whole question might be academic anyway as the shims are no longer available and I was quoted

As an additional bit of information you can see the two different scenarios on the parts fiche at http://www.cmsnl.com/yamaha-ty250-trials_model16818/ On the 250A model the shim is on the 'inside' of the main bearing, on the 250C and D model it has moved to the 'outside' of the main bearing. My best guess here is that the early version of the fiche had an error which was corrected on the later versions, but I would still like to hear from any TY250 motor experts out there if this is indeed the case. thanks in advance! Richard

Dear All, A bit of a request for help here. I have just purchased a standard TY250E (493-300925) and am in the process of a complete strip and rebuild of the whole bike. All went well with the strip of the engine with just one item 'missing' and there is a contradiction between the repair manual I have and the on-line parts fiche I have looked at. So here's the problem: In the workshop manual it says to install a shim on to the primary drive side of the crank before installing it into the crankcase half (So the shim fits between the crank flywheel and the main bearing inner race). But when I look at the parts fiche it shows the shim fitted on the outside of the main bearing so that it fits between the main bearing and the primary gear. When I stripped the engine there was no shim fitted at all. So....does anyone know the correct position for the shim? All help and suggestions gratefully received. cheers Richard