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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Wiseco Piston Clearances
Post Info TOPIC: Wiseco Piston Clearances
dlowenst


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Wiseco Piston Clearances
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Following on my earlier post, I have removed the head, barrel and piston and determined that the existing piston is a Wiseco 4689M07350, which is 73.5 mm nominal (0.5mm over stock). While I fully recognize that it may make sense to replace the piston regardless, for diagnostic purposes I want to verify whether the existing piston/bore clearances are within spec. I have the official Yamaha TTR manual, and have taken top/middle/bottom bore and piston measurements in accordance with the procedure outlined in the manual, but I seem to recall that the forged Wiseco pistons have different clearance specs than the OEM pistons and therefore the clearance specs given in the Yamaha service manual may not be relevant for the Wiseco piston. Unfortunately, I no longer have the box or installation instruction sheet that came with the 4689M07350, and despite a lot of Googling I've been unable to find a copy of the Wiseco instructions or clearance specs.

Any chance someone has this information?

Thanks,

Dave



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dlowenst


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Thought I would close the loop and answer my own question, in case it helps out someone else in the future.

I spoke with Wiseco technical support, who noted the following:

  • Due to their tapered piston design, you only need to take measurements at the bottom of the skirt, 90 degrees from the pin
  • Piston-bore clearances should be 2 thou minimum, 4 thou maximum
  • The reason I couldn't find this information online is that they don't publish it (not clear why)

I got the sense that the above info applies to all of their forged motorcycle pistons, not just the model# 4689M07350 that I was asking about.

Dave



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TTRfan


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Thank you for feeding the info back thumbsup.gif



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