KMB
Addicted to ArboristSite
My compression gauge is from HF, I know cheap. I recently replaced the tester’s schrader valve with a new one from Snap-on (the tester was giving inconsistent readings and then it stopped reading period). Tests done cold.
Stihl 044 = 140 psi
Stihl 260 = 170 psi
Olympyk 970 = 185 psi
Shindawia T260 (string trimmer) = 165 psi
(friends Stihl 028 WB = 160 psi)
With the exception of the 044, all have original pistons and cylinders. The string trimmer and friends 028 are stock, the 260 and 970 have muffler mods, and the 044 has a DP cover. I believe my compression tester is working properly. The 970 reading of 185 psi definitely feels right when I pull the saw over. The other readings sound about right…except for the 044.
The 044 bothers me. A bit on the history of the saw (rebuild was completed at the end of February 2008). I got the saw as a non-running project. The piston that was in the saw had some scoring on the intake side. The saw pulled over, and the compression felt good, but I didn’t get a compression tester until the saw was mostly apart. I now know better and will check compression on any new project saws before taking apart.
The original piston, that was in the saw, had some scoring on the intake side. I cleaned up the cylinder with a little acid, gave it a light hone (just enough to get the cross hatching using a Silicone Carbide 320 grit Flex-hone) and put in the Bailey’s ($25 or $30) piston and rings (I don’t think they had the other 044 piston options at the time I bought mine). I know OEM is better, but this was a budget build. I got a new base gasket from my local dealer. Again, I know better now…I should have measured the new gasket thickness. It was my first rebuild, but I made sure that the piston was in the right direction (arrow pointed toward the exhaust). I should add that I had also did vacuum and pressure tests which the saw passed. After the saw was together, I did what I believe is called ‘heat cycles’ where I let the saw idle fairly high for a few minutes, then let it sit for a few minutes, then let it idle fairly high…and so on a few times. I had replaced the original starter handle with an elasto-start handle, and the compression has always felt low. I should have recorded the first cold compression test, but I think it was about 135-140 psi. I thought that as I used the saw, the rings would seat and compression would go up. To me, having only run one other 440 to cut a few cookies one time, my 044 ran good and I was impressed. But after many tanks (don’t have a record) the compression is only 140 psi.
To me that sounds low for having the top-end rebuilt and with enough break-in time. Maybe it needs more time? Compression issues usually mean dealing with the rings, I guess new rings should be tried first? Try a new base gasket? I question the base gasket because it was an aftermarket one, and I don’t know if it is thicker than an OEM one. The saw idles fine. ‘Seems’ to run strong in the cut…but maybe I don’t know how ‘strong’ this saw can really be with proper compression. I don’t think I need to do another vacuum and pressure test. I don’t think this is it, but do I need to try another piston (and rings), and a different base gasket? Anything else I’ve missed? I’m thinking that the compression should be about 160 psi (cold, after break-in, stock base gasket) after a top-end rebuild for this saw…from what I have read here on AS from the knowledgeable members.
OR…just run it…but I think there should be more potential out of my saw as it is (stock base gasket).
Pics of piston through exhaust as the saw is now (not the best pictures with using the flash):
What say y’all.
Kevin
Stihl 044 = 140 psi
Stihl 260 = 170 psi
Olympyk 970 = 185 psi
Shindawia T260 (string trimmer) = 165 psi
(friends Stihl 028 WB = 160 psi)
With the exception of the 044, all have original pistons and cylinders. The string trimmer and friends 028 are stock, the 260 and 970 have muffler mods, and the 044 has a DP cover. I believe my compression tester is working properly. The 970 reading of 185 psi definitely feels right when I pull the saw over. The other readings sound about right…except for the 044.
The 044 bothers me. A bit on the history of the saw (rebuild was completed at the end of February 2008). I got the saw as a non-running project. The piston that was in the saw had some scoring on the intake side. The saw pulled over, and the compression felt good, but I didn’t get a compression tester until the saw was mostly apart. I now know better and will check compression on any new project saws before taking apart.
The original piston, that was in the saw, had some scoring on the intake side. I cleaned up the cylinder with a little acid, gave it a light hone (just enough to get the cross hatching using a Silicone Carbide 320 grit Flex-hone) and put in the Bailey’s ($25 or $30) piston and rings (I don’t think they had the other 044 piston options at the time I bought mine). I know OEM is better, but this was a budget build. I got a new base gasket from my local dealer. Again, I know better now…I should have measured the new gasket thickness. It was my first rebuild, but I made sure that the piston was in the right direction (arrow pointed toward the exhaust). I should add that I had also did vacuum and pressure tests which the saw passed. After the saw was together, I did what I believe is called ‘heat cycles’ where I let the saw idle fairly high for a few minutes, then let it sit for a few minutes, then let it idle fairly high…and so on a few times. I had replaced the original starter handle with an elasto-start handle, and the compression has always felt low. I should have recorded the first cold compression test, but I think it was about 135-140 psi. I thought that as I used the saw, the rings would seat and compression would go up. To me, having only run one other 440 to cut a few cookies one time, my 044 ran good and I was impressed. But after many tanks (don’t have a record) the compression is only 140 psi.
To me that sounds low for having the top-end rebuilt and with enough break-in time. Maybe it needs more time? Compression issues usually mean dealing with the rings, I guess new rings should be tried first? Try a new base gasket? I question the base gasket because it was an aftermarket one, and I don’t know if it is thicker than an OEM one. The saw idles fine. ‘Seems’ to run strong in the cut…but maybe I don’t know how ‘strong’ this saw can really be with proper compression. I don’t think I need to do another vacuum and pressure test. I don’t think this is it, but do I need to try another piston (and rings), and a different base gasket? Anything else I’ve missed? I’m thinking that the compression should be about 160 psi (cold, after break-in, stock base gasket) after a top-end rebuild for this saw…from what I have read here on AS from the knowledgeable members.
OR…just run it…but I think there should be more potential out of my saw as it is (stock base gasket).
Pics of piston through exhaust as the saw is now (not the best pictures with using the flash):
What say y’all.
Kevin
