Bump. Jerry and Carl what do you think of these pistons for the 250/zilla?
They are made by ART the Japanese piston company that makes Suzuki OEM cast pistons. I have used a lot of them over the last 30 years in OTHER engines where the OEM pistons are reliable. The OEM piston is not reliable in a modified or and engine that the clearances get a little loose. They will shatter in the LT500 just like the OEM piston. The skirts are too thin.
I also have some of these if someone needs a piston for a completely stock engine that will never be over-reved or punished.
Jerry, while your here, what is a good piston for high compression/high rev 250s and 500s? I always had good luck with vertex black coated pistons in high revving 125cc bikes. They don't list them on vertex's site for the LT250. When I was wrenching on 80s 100s and 125s they made a high compression piston for stock bore bikes that didn't require any machine work. They were awesome in my YZ125. Does anyone make a similar piston for our applications? if not, have you ever applied the black moly coating on any of your builds?
Pretty much the only forged piston for a QR 250 or 500 is a wiseco. As jerry stated the skirts are weak on the cast pistons. The wisecos are much stronger, though eventually the skirts will crack on them as well.
10-4 bad moon. Hopefully another manufacturer like vertex will get smart and make a better piston for us. There's still quite a few to be sold.
I've talked to a JE racing pistons rep at a stock car race last year. He said they could make any piston we want, but I haven't had time to pursue it farther. Maybe somebody could contact JE and find out?
Large displacement (generally anything 250cc or above has problems with two-stroke forged pistons collapsing.
Wiseco and Wossner seem to be the worst with the collapsing problem. Record the measurements on a new LT 250/500, KX 250/500, CR 250/500 , etc. piston with the correct clearance and run it for a weekend. Take the pistons out after a weekend of racing or hard running and measure it and compare the dimension to the dimensions of the new pistons.
You will usually find that where the largest diameter was on the new piston's lower thrust sides of the skirt is .003" to .007" smaller than it was when it was new. You will usually find that where the smallest diameter was on the new piston (just below the wrist pin and parallel to the wrist pin) is now .003" to .007" larger than it was when it was new.
The conventional piston design that the forged piston manufacturers are using does nothing to prevent the collapsing problem. The cast piston's alloy is hard enough that is much more resistant to bending (collapsing) but is too brittle and weak for the conventional cast design for the load they are experiencing in the high RPM modified engines.
We do not have much choice at this time but to use the soft collapsing forged pistons in the big-bore long-stroke single cylinder two strokes.
A forged Wiseco piston will run for some time before the cracks will propagate to the point where a skirt will break off and turn your engine to junk.
A severely over stressed cast piston may not go very many engine revolutions from the time a crack starts until the piston breaks into many pieces.