So I’m a bit confused and I’m not sure what’s going on with my saws. So I have 2 echos, a 4910 that probably hasn’t had 3 tanks of gas through it and I recently bought a 3510 for my wife to use, it has maybe had half a tank through it, if that. Both run fantastic. No scoring on cylinders or anything like that. Brand new saws more or less. I bought a compression tester off Amazon, it was a cheapy one, maybe $25 and both saws are reading somewhere between 75-100psi. I thought the tester was a lemon so I bought another off Amazon, a different one but still a cheapy. I tested them again on the new tester and both are still 75-100. If this normal? I thought saws were supposed to have like 150 psi? Is it because they are so new?
Chainsaw compression
- Thread starter bridges90
- Start date
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Should use a test gauge made for small engines.
I use the first type. Works well.
https://www.ebay.com/itm/176158798965
https://www.ebay.com/itm/2659938404...t2IBNRveKEO+EOnYQCGhQEe6Y0|tkp:Bk9SR4ih-a3VYw
I use the first type. Works well.
https://www.ebay.com/itm/176158798965
https://www.ebay.com/itm/2659938404...t2IBNRveKEO+EOnYQCGhQEe6Y0|tkp:Bk9SR4ih-a3VYw
May have to run a few more tanks through them. Not sure on the echo saws but most of my Stihl's were 7-10 tanks till broke in.
They won’t run at 75-100 psi. The gauge is at fault or not suitable for small engines.
thompsoncustom
ArboristSite Operative
probably the wrong schrader valve in the end of it which you can swap out.
This is why I don't use compression gauges on saws. Never know if you are getting a correct reading. Hold by the starter handle. Should stay up or release slowly. If not holding, time to Check sparkplug tightness, Decompression valve and/or remove the muffler.
OP you said both saws run fantastic, so why waste time with all this ?
Moreso just curiosity than anything.
Had two MS201TC in shop. Customer says low compression. Held up by the handle, did start. Pulled muffler, perfect piston. Passed pressure and vacuum tests.
Real issue, chain not feeding and they were pushing on it. Plus an off brand chain I have never seen. Smallest 3/8 low pro I have ever seen. 50 gauge.
2nd saw, had someone helping at their shop. You have to put all the pieces back in the carburetor. Works better that way.
Real issue, chain not feeding and they were pushing on it. Plus an off brand chain I have never seen. Smallest 3/8 low pro I have ever seen. 50 gauge.
2nd saw, had someone helping at their shop. You have to put all the pieces back in the carburetor. Works better that way.
Had a similar problem with a stihl 170 and 181. I was using an adaptor for the smaller hole on the 181. That put the shrader valve farther away from the combustion chamber - effectively increasing the size of the chamber and causing lower readings. The shrader valve must be on the end that screws into the spark plug hole.
Adapters are well known to do that, effectively increasing the cc`s of the combustion chamber.
I was able to machine an old tire valve to fit in the end of the adaptor. Still used the correct shrader valve. Compression was fine then.
I had to make an adapter for the new smaller sparkplugs on the Husky 5xx series. All the compression testers I could find, used an adapter for this smaller plug. I took one of the adapters and modified it to put a compression tester Schrader valve at the very end. It changed the readings on a 562xp by 15 or 20 psi.
So what does it read on your saw now?
At the time, I was rebuilding my brother's 562 on a new bottom end. I don't recall exactly but it was over 150psi when using the modified adapter. Using the unmodified adapter had me thinking that there may have been an issue with the ring/piston/cylinder/decompression valve.
WI_Hedgehog
You bought a WHAT???!!
The problem is likely that on a small engine the cylinder volume where pressure is built is relatively small (at least compared to a car engine). The compression tester hose increases the cylinder volume significantly, and as the piston only displaces a small volume the pressure that displacement can make is therefore lower. In automotive compression testers the one-way valve that allows the gauge to retain the highest reading until the pressure release valve is pushed is located near the pressure release valve.
Small engine compression testers have a one-way valve located at the end of each adapter hose near the cylinder. This hose still adds volume to the cylinder and the saw has to be pulled several times to build compression, but when cylinder pressure is released through the exhaust port the hose pressure is trapped in the hose by the one-way valve located at the end of the adapter hose near the cylinder, allowing for a true pressure reading. Multiple one-way valves require more seal maintenance (given there are more valves to maintain) and are more expensive due to greater manufacturing costs, which in an automotive application is pointless.
Depending on several factors and as a general guideline, compression should be at least 125 PSI; on a new saw 135-145 PSI, higher on some models/brands, 155 PSI and above on ported saws. Disclaimer: I don't build saws, just run them mainly, and not for a living.
The Mityvac MV5530 was suggested by other members, I bought one and it is a quality kit that works well. $75 on Amazon.
It isn't clear from the pictures and I can't find any description of the adapters. Do each of the four hoses and four adapters have a Schrader valve at their ends? If not, this would not be appropriate for chainsaws and other small displacement engines.
WI_Hedgehog
You bought a WHAT???!!
Each of the four hoses and if I remember correctly the four adapters also have a Schrader valve at their ends; I had wondered the same thing and was impressed with the set. If you want I can look tonight.
Maybe that is why the compression tester for the 4 mix machines has no hose.
Some info about compression testing small cc engines.
https://www.arboristsite.com/threads/compression-tester-issues.310133/
https://www.arboristsite.com/threads/compression-tester-issues.310133/
