New compression tester from Baileys.

[Little Al]

I believe the Schrader valve and relief valve are factors. I have two gages and there was a 30psi difference. I got suspicious (sp?) and traded the gages between the relief valve/flex tube/schrader assembly. Low and behold the readings were reversed. In other words, the gages were consistant when used with the same flex tube assembly. I suspect the higher one is correct. I believe the Schrader and the relief valve may be late to crack open.

Some one argue with me.

I have been told( don"t know if it"s fact)that auto compression testers more likely than not will be fitted with the wrong schrader valve insert, again told that the correct one for saws/ strimmers etc. should be coded white, the auto ones blue, have no idea if this is fact or fiction but would seem to bear out as the 2 different ones I have give different readings on the same saw Have also been told that Snap On carry the different rated ones

 

[Coldfront]

I got mine for $5 at a yard sale. Never used, receipt in the box ($39.95 at local auto parts store).

I like to test all my saws...

036 Pro (Sold! )
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Dolmar 7900...
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Jonsered 2171 w/ new Meteor piston and base gasket removed...
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I would have to believe that the quality of the rubber hose would have a lot to do with it also. The one in the pictures above has a steel braided hose. I know on hydraulic hose a 4 wire is much more expensive than a 2 wire hose. I'm sure the cheap testers use cheap hose maybe no wire at all. Rubber expands like a balloon, it has to affect the readings also. With multi cylinder engines you use the tester to look at readings for a big difference between cylinders like a 3 or 4 cylinder outboard motor. With a single cylinder engine you can't do that, you have to know your tester. I bet if 4 of us tested the same engine with our own testers we would have 4 different readings. If you made a tester with a steel tube instead of a rubber hose I bet your readings would go way up.

 

[Mike Boyer]

2 things i've done, Shortened that hose to where it is basically now 2 stubs lined with copper refrigeration tubing Slightly swaged and clamped (Apparent comp.# went up from 120 to 145),, and then on bigger saws I clamp the powerhead to my 500# Fab table benchvise via the bar, and use my Milwaukee "Hole-Hawg" with the appropriate adapter to spin the crank, usually via the flywheel--I turned down a rod of nylon and cut some grooves in it to fit the 044 center where the pawl catches. (with the pull cord cover off of course, And surprisingly, outboard clutches are sometimes tight enough that even that will work--I had a Husky once that was So tight that even my 1/2 drive twin hammer I-R impact gun wouldn't break the clutch loose without a friends firm heavy gloved grip on the flywheel. And thats on a gun that makes 450Ft./Lbs. in reverse at 90 psi! I thought something was gonna break fer sure! or at the very least twist the crank...But that same saw still runs just fine to this day.

 

[Coldfront]

Just goes to show that if your cheap compression tester only reads 110 psi, don't automatically think you need new rings or piston because other guys are getting 150 psi on there testers.

 

[GrassGuerilla]

So, if the cheap gauge with the "ballon rubber" hose, and a schrader valve in the wrong end reads 195 psi. What do you think it really measures?