piston confusion....

[woogie_man]

Ok I currently have a flying horse 66cc motor and I have ordered a replacement piston for it. I was under the impression that these motors were a copy of the pk80 motors. So I bought a piston for one of these motors and installed it, only to find that I am hitting the cylinder head. So I installed the 4 base gaskets that I had as well as the metal head gasket and it is still hitting, though I am able to get the piston to travel through the entire stroke. I am seeing, or should I say hearing, the piston hitting the cylinder head.

I ordered the piston through Ebay, through a very nice lady that has helped me out while the post office has managed to loose my first package. So it has a bit of a wait, but the piston is very nice.

Is there any harm in using more base gaskets until I get the piston from hitting the head? I can always get longer bolts from work, so that isn't an issue. I just want to make certain that I am not going to harm the motor in any way.

 

[Agreen]

Well, that is increasing the case volume, which lowers the crankcase pressure. So that could be a slight issue. Any pics of the pistons side by side? I heard a few of them have had a high wristpin, where others have had lower wristpin, which raise the compression ratio. If it were me, I'd fabricate a shorter conrod and balance the assembly... but I know that not everyone can do that

 

[woogie_man]

Yah I can get a few pics tomorrow.

Though when looking at them before the install the pin location looked to be the same height, though the new piston appeared taller.

 

[crassius]

flying horse & skyhawk nave pistons with the wrist pin hole 5mm higher than standard pistons (when measured from bottom of skirt - 25mm vs 30mm)

many motors that use these pistons have longer conn rods and, at least some, have a longer stroke built into the crankshaft

while spacing the cylinder can make it work, you might find that port timing changes quite a bit

mzmiami on ebay sells both kinds with pics of the diff