Yamaha TW125 Engine??

[nareik88]

Hi all, im completely new to this (as i know youve heard many times)

Ive started building a Yamaha TW 125.

I got a Yamaha SR 125 Engine as i was told they are nearly the same.

I have the put Engine in the TW frame and it all fits, but the sprocket on the rear wheel is not inline with the sprocket on the engine.

The rear sprocket sits more left to the other sprocket so the chain would end up going diagonally.

The engine sprocket is not secure just loosely pushed onto its bolt.

Ive added a photo so i hope this helps...

Any feedback would be much appreciated.

[Teflon-Mike]

That looks about right!

PW has baloon tyres, so the engine, though probably pretty much the same as the SR lump, will probably have a longer gear-box out-put shaft to locate the sproket further out, so that the chain run clears the tyre.

Probably a few other detail changes as well, like the engine cases to clear the re-located sproket, and the gearing to suit the different sized wheels & tyres.

So, we can see the problem........ whats the question?

I presume its 'how to I fix this problem'?

Well, the 'propper' way of fixing it would be to get the right engine for the bike your rebuilding!

Working with what you got?

What have you got?

Do you have the original PW engine still? Even if it doesn't work or is in many pieces.

MAY be that the PW motor used an extension on the output shaft, rather than a different out-put shaft..... if so, remove that from old engine, fit to new.

If not, then you will probably have to take the new engine apart and swap the out-put-shafts and any other parts that are different.

Alternatively, you could look at it from the other end, and try and get the rear wheel sproket to line up with the engine sproket.

Possible that a spacer could be made to bolt behind the engine sproket to push that out-board a little, and the hub could be milled to bring that in a little..... but looking at the amount of off-set between the two you need to correct, think you'd be struggling.

Personally, I'd be looking at getting the gear-box sproket out-board where it ought to be, either with the right engine, or bits from teh right engine, or some HD engineering tomake up spacer long enough to mount the sproket that far out, & apropriate covers.

NOT an easy fix I'd imagine, which ever way you go.
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[nareik88]

Thanks for the reply.

I don't have the original TW engine. I bought the SR engine as it was a cheaper option and all that was available at the time.

I will have a go at the advice you gave, I'll keep an eye out for a TW motor exstention and various parts.

Might also try and get the rear sprocket inline with the engine. Have the make sure it's not going to conflict with the wheel though.

Trial and error i suppose.

Thanks.