TOPIC:

seem common in auto engines but not bikes.
or is the offset so much less that i've not noticed?

-Duck

Post edited by: Duck, at: 2006/01/22 05:42

Just conjecture on my part, but it seems to me like most motorcycle pistons probably do have offset piston pins. otherwise there would not be a front and back to a piston. If a piston must be installed with some kind of mark towards the front, then pin offset is the only reason I can think of for doing that in an engine with symetrical valves and combustion chamber.

If my thinking is wrong, I'm sure someone will correct me

the valve reliefs are different from intake to ex(36mm-vs-30mm),that is the reason they have arrows/marks to the front.

craigpuckett wrote:

the valve reliefs are different from intake to ex(36mm-vs-30mm),that is the reason they have arrows/marks to the front.

Have you measured the valve reliefs or are you making an assumption based on the different valve sizes?

Your answer actually made me get off my lazy butt and go out to the (cold) garage and measure a set of new GPz750 pistons to see if that was true (I don't have any 1000 pistons).

The valve reliefs on the GPz750 pistons are the same size, and the piston pin is offset. Same thing applies to the 750 twin (I measured a new set of those while I was there), I don't know that it applies to the 900/1000 pistons though, because I don't have any to measure.

Since I still have my coat on, I may as well go get the 750 twin frame measurements that someone else needed. See what you started!

Many oem use offset pins ( usually torwards it intake) to lessen piston slap. Somer car racers found out that if the pistons were installed backwards, it made more power because of a more favorable rod angle. They used to due this in some stock classes where the rules stated oem pistons only, but didn't say they had to be installed correctly.

Jay

you are right about the offset Steel on a gpz1100 piston,but they also have different size valve reliefs.

and yes Jay it is to the intake side.

my assumption was based on the valve reliefs

craigpuckett wrote:

you are right about the offset Steel on a gpz1100 piston,but they also have different size valve reliefs.

and yes Jay it is to the intake side.

my assumption was based on the valve reliefs

Well, if someone were to give me a GPZ1100 and a big bore kit for it, then I'd know that.

But at least the person that wanted the KZ750 frame measurements got them

Post edited by: steell, at: 2006/01/23 00:23