question about mcculloch pistons

[david a luciani]

hi,
this is a what the heck is this question.
yesterday i was cleaning parts for a couple of mc10 clones.
the first block i grabbed had a scratched bore .
i didn't feel like digging out the hone so i went to get a different one from the pile and i noticed something weird.

two of my chainsaw powerheads had two sets of ring lands.
a thick set that have the rings installed and a thinner set that aren't being used.
the thicker set is machined below the thinner set.
out of curiousity i checked some others and discovered two more with pistons like this.
did mcculloch just re-cut the old gokart pistons for use on chainsaws?
or were there replacement pistons that were set up for use in kart or chainsaw engines maybe.

when i get a chance i'll get some pictures out here for you guys to see what i'm looking at.
dave

[Dennis Turk]

One thing you mite take a look at is the two unused ring grooves are they going to cause you to loose crank case pressure when these open ring grooves are between the intake and exhaust ports. I have always wondered about this. I was up in Tacoma Washington early this year for a vintage cart show at there indoor rent a cart track. The owner of the place took us over to his cart shop and in driving over I asked if he had ever ran a Homilite engine back in the day. He said the only way we got them to run was without any rings or ring on the piston. This has made me curious because the Clinton E-65 use the three 1/16 inch chain saw rings and have wondered what would happen if I took one or two of them out.

Turk

[david a luciani]

i really need to post pix of these pistons but i'm nowhere near the camera.
the top ring land is a thin ring.
then the thick chainsaw ring then thin then thick.
i suspect for common chainsaw power that thin gap wouldn't steal enough pressure to matter.
my guess is that mcculloch found themselves with a bunch of stock bore kart pistons that were made obsolete by the larger bore sizes of the later years.
So mcculloch , like any good penny pinching company , reworked the pistons to fit chainsaws.
only someone anal like me ,tearing down old saws, would ever notice anyway.
but it's interesting in that it may allow options for stroking older motors.
Dave

[david a luciani]

update,
pulled the motor with the strange piston apart today as it needs new main bearing.
the second set of cuts aren't ring lands just a circle around piston.
i compared them with a mc kart piston and the top slot is in the same place.
my best guess now is huh???
anyway will take a pix when i get my camera in the same area code again.
dave