piston confusion....

GoldenMotor.com

woogie_man

New Member
Aug 9, 2013
223
0
0
Fargo, ND
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

Member
Feb 10, 2013
792
11
18
Southeastern GA
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

New Member
Aug 9, 2013
223
0
0
Fargo, ND
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

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
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