Wiseco Piston part number Q's, TR 675cc BBK.

Hi, I just got everything back from Thumper Racing after alomst 3 weeks. Open up the box and check for everything: cylinder looks good, clutch springs, new plug and oil filter, all the right gaskets but when I opened up the piston I knew something was off... The part number for the piston is 9887M10241, says "Thumper Honda XR600 Dished-102.4mm." I went on their site b/c this does not look like a 10.25:1 compression piston, hell the stock piston is a flat top pretty much, this one has a pretty big dish. I tried calling TR but they closed down the phones early so I left them a message. This is what a was dreading, having the engine apart for this long and something like this happen, I still dont know for sure about the piston's CR b/c I cant even find it on Wiseco's website :). Also, I put the piston in the cylinder to see how close the fit was gonna be and the was some play! Its a full floating piston (if that changes anything) and it just feels too loose from what ive seen in terms of specs. I should measure everything before I start frekin' out...

Just one more thing, which way does the piston go in? There is nothing where it says Intake side or Exhaust side or does it not matter? For the piston rings, I am assuming that the black ring is the 2nd compression ring and the top is the one with the copper/chrome ring around it. There is no markings to which way the rings go either, usually ther is something so you put them in with a marking upwards or something... So if anyone has any info on this piston I got from TR and if this is the 10.25:1 (dont see how) or not, PLEASE let me know! Thanks a Million!!





Zack Z.


Is that stock piston the stock comp ratio, If so they look about the same..

The stock piston is cast and the new piston is forged and a forged piston requires more clearance, take some feeler gages and slide between the piston and cyl. wall to figure out the clearance, they should slide with the piston easily,just a slight drag....

the rings should have marks that go up or if there square cut, can go up either way, You right the black ring is the second ring and the shiney faced ring is the top one.......... :)

Thanks for the help frankstr! I called up TR and I guess they no longer do the 10.5:1 piston?? I'm a little pissed b/c that would have been nice to know b4 I did all this... I would have just degalzed the cylinder and bought the Wiseco 10.25:1, 100mm piston and be done with it. So its a 9:1 piston in right now, so thats that one. Thanks agian!


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