when to change piston ring???

[jbgorecom]

How does one know when to take engine apart and change the piston ring(s).

I have 2 dolmar's,
model 110 with 145lbs compression
model ps-341 with 115 lbs compression
Both saws the cylinders look good, no scratch's. looks like they were well taken care of.

With no service manuals for these saws, how does one know??????
Or can a member help????

jbgorecom

 

[timberwolf]

If saw is still running well at 145 psi, then can be left be till you need a rainy day project.

Pull the other one down it has problems. Inspect bore, check piston fit, also measuring ring gap can help determine just how worn rings are, something down in the .010 to .020 is ok, but if ring gap is over that they are getting worn. Sometimes on 2 ring pistons just swaping top and bottom can bring things back for a while as the top ring does most of the sealing and wears quickest.

 

[redunshee]

If saw is still running well at 145 psi, then can be left be till you need a rainy day project.

Pull the other one down it has problems. Inspect bore, check piston fit, also measuring ring gap can help determine just how worn rings are, something down in the .010 to .020 is ok, but if ring gap is over that they are getting worn. Sometimes on 2 ring pistons just swaping top and bottom can bring things back for a while as the top ring does most of the sealing and wears quickest.

How much compression improvement can one expect from replacing rings? For example in the two cases you related, if everything is equal would they both end up with similar compressions?

 

[timberwolf]

Sorry I don't have a crystal ball. If compression is bad due to a worn ring you could expect compression to go back into the 160PSI range. But if compression is bad in part due to damage to the cylinder and or piston a ring won't help that much or at best, improvements won't last that long.

In general though, by the time a ring is totally worn out the cylinder and piston are less than perfect too. Improvements can be made re-ringing, but rings can't make up for a damaged bore or worn piston.

 

[jbgorecom]

Thanks timberwolf. I know every saw make would be different, but what would an average compression be on a good or newer saw. I have no idea since I have not had any newer saws. I just purchased 10 saws for $70.00 from a guy. none of them run, but going to check compression and cylinders for scratches. All of them were box store, poulan, mcculloch, sears, homelite. Will either fixup and sell as whole, or as parts, or as junk.

any advice would be helpful.

MERRY CHRISTMAS

jbgorecom