stunthanger.com

Engine basics => Engine set up tips => Topic started by: RDJeff on November 09, 2011, 09:30:44 PM

Title: FP40 Question
Post by: RDJeff on November 09, 2011, 09:30:44 PM
I just picked up my sixth FP40 on the auction site, and this one is different from the others in that there is a hole in the piston skirt.  What have I got here?  The hole is about 1/4" in diameter, and appears to be machined that way.  I can see the rod ond pin through the hole.  I'm used to older two-stroke motorcycles having holes in the piston skirts, but they are in the intake face, while this is visible throught the exhaust port.  Interesting...
Title: Re: FP40 Question
Post by: Curtis Shipp on November 10, 2011, 06:25:35 AM
Piston in backwards.
Title: Re: FP40 Question
Post by: RDJeff on November 10, 2011, 12:15:24 PM
So, why didn't I think of that? ???
Title: Re: FP40 Question
Post by: Geoff Goodworth on November 12, 2011, 04:50:41 PM
I have several FP 40s—both steel liner and ABN—and the only holes in the piston are for the wrist pin. None have a hole in the side of the piston.

I'm going to guess that it's been modified and the piston is in back to front.
Title: Re: FP40 Question
Post by: Dennis Moritz on November 13, 2011, 07:06:21 AM
Not stock. FP pistons don't have that hole.
Title: Re: FP40 Question
Post by: RandySmith on November 13, 2011, 03:40:04 PM
Not stock. FP pistons don't have that hole.

Yes FP pistons  did have that hole from OS in early motors

Randy
Title: Re: FP40 Question
Post by: RDJeff on November 14, 2011, 09:53:41 AM
It looks like I need to take apart some of my FPs in order to see what's what! 

Randy, if the hole is standard on older engines, do you think my piston is in backwards?

Thanks everyone for the responses!
Title: Re: FP40 Question
Post by: RandySmith on November 14, 2011, 10:21:57 AM
yes  the piston is more than likley in backwards, check the rod also if it has one side of the bottom "chamfered" put it toward the crankshaft

Randy
Title: Re: FP40 Question
Post by: RDJeff on November 16, 2011, 09:41:35 AM
Thanks Randy, I'll give it a look!