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I've had a few inquiries about pistons in over sizes greater than 52.90. My sources tell me," It ain't gonna happen".

The displacement limit was raised to accommodate those running large clearances and a 52.90 piston, not to "Save Cylinders".

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Jean Stafford

"Never argue with an idiot. They will wear you down to thier level, then beat you with experience."
"Nothing is foolproof, for a sufficiently gifted fool."

My thought is that wka actually f,d up a little. Somebody said let em run 90 pistons and they upped the bore size to 2.090. Check the minutes from wka on this one. I think they spoke without thinking and accidentally spoke in standard and metric at the same time

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John,

WKA''s rules previously used bore size to calculate the maximum dispalcement. Bore ^2 x .7864 x Stroke. Using this method, .90 pistons were not legal in long stroke motors. Now they are, and builders who choose, can let them rattle.

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Jean Stafford

"Never argue with an idiot. They will wear you down to thier level, then beat you with experience."
"Nothing is foolproof, for a sufficiently gifted fool."

I didn't know there was such a thing as a long stroke motor?????

Check the math jean. I bet you will prove yourself wrong. I have done the math with the old measures and max bore times max stroke don't get close to max cc

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Can you get a 0.006" clearance and still stay within the max displacement?

Stroke tolerance is 0.0039", so you could have a stroke of 1.815 +/- 0.0039"

If you so the math, I believe you'll find you couldn't run a 1.819 stroke amd a 52.9 bore. You can't use the piston diameter, it must be the bore.

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Jean Stafford

"Never argue with an idiot. They will wear you down to thier level, then beat you with experience."
"Nothing is foolproof, for a sufficiently gifted fool."

Max stroke x max bore....max is max..there is no tolerance.

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	John Horn wrote:
	Max stroke x max bore....max is max..there is no tolerance.

Do What!!

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Jean Stafford

"Never argue with an idiot. They will wear you down to thier level, then beat you with experience."
"Nothing is foolproof, for a sufficiently gifted fool."

Okey Dokey...here we go...gonna teach an old dog a new trick...and you all said it couldn't be done...lets see.

Pg 101 of your new 2013 WKA Rulebook Section 503.1, clearly states the calculation for calculating cubic inches
Bore x Bore x .7854 x Stroke
Pg 109 section 601.4 clearly gives the max bore at 2.090 and the max stroke at 1.816. I think that you can agree that MAX=MAX right...there is no tolerance on a max value

So...pretty simple math here...2.090 x 2.090 x .7854 x 1.816 = 6.230 cubic inches.

6.230 cubic inches calculates out to 102.09 cc

the max allowable cc is 102.11 so we are nowhere near the max cc yet

If you figure out a 52.98 MM piston with .004 piston clearance i think you will find that it fits just fine...i wouldn't want to run it very long like that as it may be very close on the bore size...but then again, read the WKA minutes and you will find that the supposed reason they are allowing the 52.90 piston is so that they don't have to spend the money on the bore measuring equipment. Not sure where the logic is in that...it is only a 2" snap gauge and a 2-3 inch micrometer...but I am just a dumb carpenter, what do i know about measuring.

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So, "Nowhere near.." equates to 0.02 cc ?

Head volume is measured in 0.1 cc. Just a couple of thousandths on the bore size will make it illegal.

This change that WKA made was to sell 52.9 pistons. Builders using the old, 2012, information, could not use a piston greater than 52.85 in a long stroke engine, using 0.005" or larger clearance. raising the cc limit, allows then to be used like this, so more pistons of this size will be sold.

Using smaller clearances would allow slightly larger pistons to be used, but would result in the same thing as now with the top size piston.

Still ain't gonna be any Yamaha pistons larger than 52.90, from what I'm told.

One other thing. If you'll measure a Yamaha piston, and an IAME piston, you'll find that IAME places the clearance on the piston, that is the piston is smaller than the bore. Yamaha pistons measure what is stamped on the piston, so the bore must be larger than the piston for clearance.

_________________
Jean Stafford

"Never argue with an idiot. They will wear you down to thier level, then beat you with experience."
"Nothing is foolproof, for a sufficiently gifted fool."

Last edited by Jean Stafford on Fri Feb 15, 2013 3:02 pm; edited 1 time in total

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