About compression?

[vintage red saw]

compression test

Check the compression on a good running saw to get a baseline of what the gauge is telling you, My compression tester has a leak or wont let it go above 125 psi ?, no matter what saw is hooked to it. Gives me a baseline, but not something i am going to trust.

I have the same problem with my tester I can only get around 110 psi tested on 3 saws but it does give me an idea of what is acceptable

 

[ROWDY]

I might get the unite out tonight or tomorrow and look at a few things. So far I'm thinking the so called "new" seals are bad/damaged. The same tester tested 150 Lbs on two other Stihls and 140 Lbs on a Poulan saw. It could have a poor porting work is also on my mind.

 

[watsonr]

or even worse the a.m. port timing could be off causing it to free-port.

That has nothing to do with compression unless the port goes into the or near the combustion chamber. Free porting is air cross flow from exhaust to intake and usually only when the piston is at TDC as the intake air flows under the skirt and out the exhaust.

The low compression is only a couple things. Wrong ring gap, excessive piston to wall clearance the rings can't cover, leaking decomp, excessive squish, stuck rings or damaged rings and piston. Did you install a gasket? Whats the squish? Decomp if equipped closed?

Which kit do you have?

 

[Dennis Cahoon]

That has nothing to do with compression unless the port goes into the or near the combustion chamber. Free porting is air cross flow from exhaust to intake and usually only when the piston is at TDC as the intake air flows under the skirt and out the exhaust.

The low compression is only a couple things. Wrong ring gap, excessive piston to wall clearance the rings can't cover, leaking decomp, excessive squish, stuck rings or damaged rings and piston. Did you install a gasket? Whats the squish? Decomp if equipped closed?

Which kit do you have?

Freeporting can also come from the vertical edges of the piston not covering the port.

 

[watsonr]

Freeporting can also come from the vertical edges of the piston not covering the port.

I agree, it still shouldn't have anything to do with compression.... which is the topic here.

 

[boutselis]

Could the guy who replace everything put the piston in backwards?

not sure what effect it would have but I know one way is correct and the other isn't

 

[lone wolf]

Could the guy who replace everything put the piston in backwards?

not sure what effect it would have but I know one way is correct and the other isn't

Same compression and it will run but you now have the ring end gaps moving in the exhaust port risking a snag. 99 times out of a hundred or more the ring end gaps go to the intake port side as a rule there could be other cases but I am not familiar with them.