piston-cylinder clearance

[baker250r]

I know its probly in the manual... but i dont have that right now.. lol. anybody know wut the tollerances are for the piston/cylinder?

[punker69q]

here are all the specs you need

http://www.cylco.com/vtt/86-89-TRX250R-svc.pdf

[beerock]

i usually go in the middle of the high low for clearance, like .0027=.0028

[wilkin250r]

Those numbers would apply to the stock piston. If you have an aftermarket piston, those numbers may vary due to the difference in piston material and/or manufacturing processes.

Forged pistons require more clearance than cast pistons due to their grain structure and thermal expansion.

The silicone content of the aluminum will also play a factor in clearance because it affects how the piston expands.

Research the different pistons, reference your pistons spec sheet, and combine that knowledge with the specs in the manual and a little intuition and instinct to come up with your requirements.

[baker250r]

well. the reason i am asking is... i bought a powervalve last summer for my R... he said it was in good working order and didnt need work. he sent me a brand new piston and everything for it too. i put it in, and everything ran good. the piston was even coated with wutever it is.. lol, i forgot. the cylinder walls are all good, except for they have a little bit of ring ridge going on at the BDC. i wouldnt think that would be that big of a problem.

make a long story short. i think the cylinder and psiton are all good... but my friend that is a mechanic swears up and down it needs to be renickasiled. the pisotn has a bit of play in the cylinder. but i know they gotta have some. i jsut dont know how much is too much. its a wiseco piston. and pro x powervalve cylinder. maybe u guysy can help me more on this.. i dont wanna send it out and spend 200 bucks cuz my friend said so.

[punker69q]

Like wilkin said, wiseco piston are forged, so they need a little more clearance than stock cast pistons. As for the cylinder damage, it's hard to tell without seeing how bad they are, but it doesn't take much to get rapid piston wear.

Also remember, even if you need more initial clearance with forged piston, I would'nt go over the recommended honda specs for wear limit, because even if the piston expand more when hot, you still risk to grenade that motor, even more if it's a high rev motor. It's better to be safe than sorry...

[machwon]

Not sure if you measured your piston or not but these things are real hard to tell without a dial bore guage. The coating is typically only .004" thick, so if you see exposed aluminum, its definetly shot. They usually start around the exhaust port first as its the bigger port opening. I've seen CR's come in this way and riders claimed they still ran pretty good, but didn't like to start. Keep in mind too that on a new piston, you should measure at the bottom of the piston as the top is smaller.

I just had an R cylinder plated that I got back yesterday. The clearance was set at .0025-.003 for a wiseco. This seems a little tight, but I'm sure it will work.

In cast iron I have run Pro-x at .002 in the past with a long break in, and had no problems. Bigger bores, like a 310 will usually start .0034-.0037 and I would run them till .0055-.006 at most with a good piston.