What compression tester are YOU using?

[777funk]

I've been using the $20 HF automotive tester. It works but I don't think it's too accurate for chainsaws. Everything I measure is under 125 psi including a 281xp that about broke my arm every time I started it. My excellent running Stihls with like new bores and pistons measure 100psi. So I know that it's not correct.

I'd think not having much hose volume in the works may be important (maybe not). I also read about having a schrader in the the plug adapter. I do think hose volume will make a difference since it reduces compression ratio as someone pointed out in a 2013 thread here. The HF tester hose probably has about half as much volume as the saw displacement for small (30cc) saws. May not make a difference in cars since the cyl displacement is much higher.

Here's Steve's Small Engine talking about the Schrader in the end. He said he thinks it reduces the compression ratio to not have it at the end. I can't see this being the case since when it opens, you're still compressing the saw plus hose volume to the gauge. But one comment on YT said, it's likely because some of the compression has time to leak back through the exhaust port. This makes more sense.

Whatever the case, maybe I need to find something that will give me more accurate results. I like to record the compression from saws as time goes on to track when they need work.

What compression gauge are YOU using?

 

[RedneckChainsawRepair]

Sten's left and TU-21 right small engine ones I use. But long as schrader valve at bottom of longer hose ones still reads right.

We already tested this and if he said that wrong. Long hose as long as schrader valve in bottom read the same.

Couple different saws. I was checking to show dials.

Pull till it stops climbing in psi shown.

All read same when compare. TU21 25-28 shipped. Stens 65 shipped. Both small engine ones.

 

[buzz sawyer]

Got to have the schrader valve in the spark plug hole. Any farther back effectively increases the combustion chamber volume and reduces compression reading, more so on smaller CC engines. Here is an adaptor I modified to get the valve into the chamber. Before the change, I was getting 90 psi. on a Stihl MS181. Afterwards, I was getting 130 .