RE: Pinning the Piston Ring
 

I didn't absorb the weight in those specs, I was looking at the engine size so <10 lbs it is. Probably in the .40-.60 range then
Doesn't hardly seem worth it. I will have to try it and see someday on a stand.


My used 25cc homelite had .010 end gap when I tore it down... good thing as thats the smallest feeler gauge I had!!

RE: Pinning the Piston Ring
 

Yes Ralph, that's the rule of thumb I've used for years; .001" for each inch of bore size. However, I had a conversation about this with Frank Bowman and he recommends that his rings be fitted at zero end gap. I still don't quite understand why they don't end butt and cause the problem you described, but I'm running several of them and haven't had a problem. Maybe the aluminum cylinder expands enough when running, and the cast iron ring doesn't expand much...

As mentioned, the specs for a stock ring are around .003".

AV8TOR

RE: Pinning the Piston Ring
 

Another ring end Gap table on page 2 :
http://www.jepistons.com/dept/tech/d...instrc4032.pdf

They list clearances of various types of engines by usage for the different rings in a car engine.

1mm ( .039" ) per inch mentioned above is in the ball park. The mechanic who gave me this guide builds VW offroad race engines not RC.

AV8TOR : Do you recall if the Bowman ring was filed on the ends to cover the portion of the .045" diameter pin recessed down into the groove? No idea of the piston diameter on the Homelite.

RE: Pinning the Piston Ring
 

I just spoke with Frank a couple days ago. He said at that time that there is a relief for the pin in the ends of the ring.

RE: Pinning the Piston Ring
 

Yes, if you ask Frank to provide a ring for use with a pin, he will make the notches in the ring ends for you. He's done several for me. Remember that the pin has to be recessed half way into the ring land. That way the ring end with it's notch can go over it, and not be forced out against the cylinder wall.

Whoops... That's right; .003 to .004" per inch of bore is the ring gap rule of thumb for other engines. (Not .001") Haven't built a race engine in a few years and the old brain is starting to fade.... The last one I did was the 450 horsepower 454 in my Blazer about 8 years ago. Still screams...

AV8TOR

RE: Pinning the Piston Ring
 

How does this sound for timing for the 25cc Homelite?

Intake - 143
Exhaust - 158
Transfer - 112

RE: Pinning the Piston Ring
 

I guess I found the answer here:

http://www.modelpowerboat.com/Hopping-up_a_RC_Engine

That about does it for this motor.
I machined the squish out, took the case down so I have .022 deck clearance. I used a deep well impact socket and sandpaper.
Milled (filed and sanded) the back of crankcase. (stuffed it) :)
Pinned the piston and installed Bowman ring.
Removed exhaust bridge and modified timing of exhaust. Removed nub on intake.
New 11.11mm carb
Now all I need is for some snow to melt so I can get outside and test it!!

Next... homie 30cc? Poulan 32? Kioritz 16?

hmmmmm choices choices choices

RE: Pinning the Piston Ring
 

I believe it was 1/10 of a mm. for end gap or just under .004 thou.

RE: Pinning the Piston Ring
 

I tend to agree as well. When I was told the rule we were both operating in our second language. Good thing it was not some life threatening subject like how many cc or milliliters for a dosage....:)