High compression 74mm piston to suit TW/XT conrod?
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  1. #1
    Junior Member mr200sx's Avatar
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    High compression 74mm piston to suit TW/XT conrod?

    OK lads,

    I'm doing a larger cc stroked TW build with all the goodies (1996 XT225 donor engine) including possibly adding more stroke to the XT225 crank. I also want more compression than offered by the stock Yamaha 74mm piston that is being suggested. Wiseco seems to only have up to 71mm (4312M07100), while the Wossener 73mm is only 9.5:1.

    Does anyone know of a 74mm high compression (10.5:1 and higher) piston option that fits the stock XT225 conrod?

    I am contemplating a Hot Rods YFM stroker crank kit, but this requires the larger 17mm gudgeon pin piston - which gives me a choice of Vito's (10.5:1) or JE (12:1) pistons. This starts blowing the budget to smithereens though!

  2. #2
    Senior Member elime's Avatar
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    I took one of these 67mm pistons and sent it to Venolia and asked if they could make me a 70mm one.


    P7210018a.jpg

    They said for $200 no problem.

    PA130031.JPG

    It uses standard Yamaha 70mm rings and a standard Yamaha 16mm wrist pin. The rings are the same width, thickness, as the TW rings.

    I talked to a lady at Venolia and she said if I wanted another piston just to give them the work order number and they could make one. Possibly if you are interested you could give them the number but stipulate you want a 74mm piston. The other thing is the rings -- if the thickness of Yamaha 74mm rings is the same as that of the TW you would be in business.

    But be aware this will NOT be a drop in piston. All volumes will have to be measured and the dome will have to be reduced to lower the compression ratio. And the valve to piston clearance will have to be checked. BTW, the dome is solid and very thick. Plenty of metal to work with.

    If you say to Venolia "I want a piston of 11:1 compression the will work with a TTR225 crankshaft in a TW 200 engine case" they will say back to you "send us the dimensions you want and we will make it for you."

    Now if I could only find the work order number....................
    Last edited by elime; 04-20-2017 at 11:26 PM.
    Long live the internal combustion engine!

  3. #3
    Junior Member mr200sx's Avatar
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    Interesting option but I think I'm after an off the shelf option that won't break the bank. Cheers though.

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  5. #4
    Senior Member elime's Avatar
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    Quote Originally Posted by mr200sx View Post
    I'm after an off the shelf option that won't break the bank.
    I know what you mean -- cost out paces benefits. Double the cost but the benefits only go up by a half.

    For example, camshafts are expensive and the increase in performance isn't so much. You may want to avoid an aftermarket model of one.

    Best to stick with stock Yamaha parts or direct replacements. You will get the most bang for the buck. Not the biggest bang, but the best value. Good luck.
    Long live the internal combustion engine!

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