Chainsaw Repair

That's interesting .thk

-the way i did this is approximate, because i filled the chamber and cylinder up to the exhaust port roof with liquid.......without using the piston at all.

-since the piston has a raised crown, thought it would give a similar result.  the difference from edge to center was 0.038 inch.

-next time will install the cylinder over a greased piston to see just how close i was.

-also will try using a plate.

photos to follow.

Pretty interesting stuff.  Always wondered about the actual compression ratio like I was used to seeing in cars etc.  Is that what geometric  compression ratio is?

Dang way over my pea brain.  Helpppppp LOL  Figuring Compression Ratios   http://www.hydrostream.org/ArticleArchives/Compression.htm

more

edit: added the chart above to this post.

in the chart above....i wanted to pick a safe 7.3:1 trapped comp ratio;  with combustion chamber size of 6cc.
(for you regular comp folks 9.2:1; 6cc)
those two comps are considered equal in this motor, same thing.

-after measuring the comb chamber volume.......without a gasket........came up with approximately 4cc.

looking at the chart, you can see that for a 4cc chamber......the trapped comp ratio would be 10.5:1 trapped comp......(13.3:1 regular).   pretty high!!!

i figured the gasket volume to be 0.7cc.

...so out the dealer door....the volume of the chamber was 4.7cc.   this equates to 9:1 trapped.....11.5:1 regular.  how this thing stayed together is beyond me.

imo, this would not be a good idea in a larger bore. 

this saw was made in the 1970's i believe.  when i got the saw......2nd ring was ****, locating pin broke off and embedded in the bore; top ring stuck in groove; piston gouged.

.......the putty mix was homemade.

hope it helps.

-joe