Topic: Wrist pin offsets, why the difference, and is there any bad/good effects??

[Soos]

Hey all,



Been doing a bit of piston mods lately, and have found that the KZ pistons I have(650 and 750) are about 1mm offset.
But all the CB(550, 650, various 750s, and a set of 836cc overbores) all have 0.5mm ofset to the wrist pin.




Is there a gain with a larger or reduced offset?
Is this simply a noise reducing thing for the pistons(reducing the piston slap)??





l8r

[kos]

Hey all,



Been doing a bit of piston mods lately, and have found that the KZ pistons I have(650 and 750) are about 1mm offset.
But all the CB(550, 650, various 750s, and a set of 836cc overbores) all have 0.5mm ofset to the wrist pin.




Is there a gain with a larger or reduced offset?
Is this simply a noise reducing thing for the pistons(reducing the piston slap)??





l8r

Noise is one factor and the effect of encouraging the piston to start down the bore by having off set is an important factor. Don't want the piston trying to get the crank to go the other way...do we?

KOS

[Sam Green Racing]

  it would only bend the rod a little.

There is a power advantage having less offset to the pin.
I don't know if Mark has any 970 pistons about but if he has and measures the offset, I'm sure there will be little or none at all when compaired to a standard 736 K piston.
The YB921360/1 race kit pistons for the CB92R have little or no offset compaired to the CB92. When one considers that the complete race kit only adds 1bhp to the 15.5bhp motor, It's anyones guess how much power the difference in the offset makes.
It has been known for people to have pistons made with the offset the other way round in their search for more power. How much noise and wear this creates dose not matter as the components in race motors are changed from race to race. Look how long a top fuel drag motor lasts, 4.5 seconds? 
In single cylinder and multi inline motors, the offset is allways towards the inlet side other than in a motor that spins backward through a counter shaft.
Motors in a V formation have the offsets both ways for obvious reasons.

Sam.

[Soos]

thanks for enlightening me a bit there!



l8r