Thumper Racing in Texas

you need to think of what you will do if you need another piston in the future. wiseco will have standard overbore sizes. "cutting down" a piston should not be an option. to alter something like a piston is asking for trouble. it sounds like they need to press in the correct sleeve (94mm) or give you a new jug. they screwed up, not you. just my two cents.

Agreed, have them get you a new cylinder. Then send it off to Eric Gorr and get it bored and replated like it should have been. :) Steel sleeves are old technology. :D

Why would Wiesco stop making pistons?

They are in the business of selling pistons. They don't take the forging dies and toss them in the garbage. Either Thumper dosn't want to buy the minimum quantity from Wiesco or they aren't paying their bills.

Some of these aftermarket companies suck.

give millenium technolgies a call.tell them whats going on.they saved a TR ruined cylinder for me.the use aluminum sleeve replate them.they do out standing work.

Why would Wiesco stop making pistons?

Don't know, but your guess about minimum quantities makes sense. The owner of Thumper Racing says they still sell some of the 430 kits (it's just when I order it they don't seem to be able to live up to their advertised claim)

Why would Wiesco stop making pistons?

The pistons larger than 94mm (417cc) made for the 400 rod tended to be on the heavy side compared to the weight of the OEM 92mm piston. The additional rod stress that came with this extra weight caused a lot of catostrophic rod failures on engines with a lot of hours. The failure was most often seen as an elastic limit break about 30mm or so from the small end. The rod basically pulled apart like silly putty. The YZFs have always been pretty robust engines so riders tend to go too long before servicing the crank. Taking a high mileage rod and cranking up the stresses by approx ~600 lbs with a heavier piston is a great way to learn about downstroke inertial loads and metal fatigue. :) It's not a coincidence that Yamaha changed the connecting rod when they designed the 426 with a 95mm piston. The 426 connecting is an easy retrofit and is something we recommend for anyone who is going to a big bore on a YZ400F.

Would anybody please, let me know about experience with 270 Thumper Racing's up grade for CRF's? Thanks...

Would anybody please, let me know about experience with 270 Thumper Racing's up grade for CRF's? Thanks...

Alfonso this is a great place to ask about a CRF big bore kit!

I highly recomend the 270 kit.

It increases horsepressure by 238%!

Just a thought, but i'd demand a spare piston as well, just thinking of the future

Gaawd! Way to resurrect an old thread. In case anyone read the whole thread and were wondering about the outcome, I ended up splitting the case and upgrading the crank with a 426 rod. I put about 8000 miles/350 hours on that bored out cylinder/piston and rod before I recently freshened up the top end. Still going strong!

Thanks to: Beezer, Doctorchopper and SXP for your answers...And,I have an another cuestion,Thumper Racing address?...Thanks in advance!

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