Got a new compression gauge and tested a few saws

[lone wolf]

Hard & fast rules do not seem to apply, I had a 350 husky with a 346 cyl on it & decided I needed a stock 350 and put the 350 back on, first comp was only 88 or89 lbs, but started rite up & ran well, after a couple of heat cycles comp was up to 104, after running it some comp is now 118 which I think is 10 or 15 lbs. low for this saw.
I pulled it down last week to check ring gap, it is .013, should not be a problem.
I've also got a poulan wild thing that's hard to pull over, It reads 154 on the gauge, I don't see that starter lasting long.

If your gauge is accurate and you are working on the same saws like I do the rules apply very well.

 

[RED-85-Z51]

Hard & fast rules do not seem to apply, I had a 350 husky with a 346 cyl on it & decided I needed a stock 350 and put the 350 back on, first comp was only 88 or89 lbs, but started rite up & ran well, after a couple of heat cycles comp was up to 104, after running it some comp is now 118 which I think is 10 or 15 lbs. low for this saw.
I pulled it down last week to check ring gap, it is .013, should not be a problem.
I've also got a poulan wild thing that's hard to pull over, It reads 154 on the gauge, I don't see that starter lasting long.

Had me curious, i never tested the 350 i did in March, it was smoked so i put on a Hyway 53cc cylinder and Meteor piston, no gasket...ran 3 tanks of 70:1 opti2 thru it and hung it up..pulled a 20" no sweat.

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[RED-85-Z51]

I was curious if a couple drops of oil would get the 350 up higher seeing as it was bone dry and cold...it went up about 5psi wet.

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[old guy]

I was curious if a couple drops of oil would get the 350 up higher seeing as it was bone dry and cold...it went up about 5psi wet.

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Yeah, if you used heavyer oil it would be even higher.

 

[SteveSr]

The schrader valve is the key, a car or truck valve stem schrader valve should fit a compression gauge. Every 4-5 years I change the valve in mine after realizing over time/ handling/use the little stinkers start to stick, the main shaft pin gets bent, they get oil contaminated etc. The schrader valve and gauge are removed and the hose is then able to be used to pressurize the cylinder using shop air, any time this is done I replace the schrader valve. I have been using the same craftsman compression gauge since 1999!

Do NOT use a standard schrader valve from a tire as the spring is too strong and will lower the test results. The schraders used in compression testers are special low differential pressure valves.

 

[SimonHS]

The schraders used in compression testers are special low differential pressure valves.

Where can you buy them?

 

[SteveSr]

Where can you buy them?

Snap-On sells them for their tester but should work for any. Go back to the gauge manufacturer.

 

[Goinwheelin]

Good info here on the valve. Thank you.

Do NOT use a standard schrader valve from a tire as the spring is too strong and will lower the test results. The schraders used in compression testers are special low differential pressure valves.

 

[Vintage Engine Repairs]

The only time I wished my hose was shorter...

I’m jealous of your short hose red.

 

[cookies]

The snap on man just sold you a 20 dollar schrader valve lmao how can it change the test results if the pressure is overwhelming the spring. mine preforms with the same accuracy as the snap on, i have used both side by side on a couple fords and dodges with loose valve seats. The seats would sometimes drop a hair once the engine warmed up causing compression loss and misfires.

 

[RED-85-Z51]

Lisle part number is 20100...$1.89

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[huskihl]

The snap on man just sold you a 20 dollar schrader valve lmao how can it change the test results if the pressure is overwhelming the spring. mine preforms with the same accuracy as the snap on, i have used both side by side on a couple fords and dodges with loose valve seats. The seats would sometimes drop a hair once the engine warmed up causing compression loss and misfires.

Automotive gauges don’t normally have a valve in the end of the hose

 

[cookies]

automotive gauges are electrical

 

[old guy]

I have two gauges, the first one with the longer hose came from an auto parts store, $29.95 it has the schrader in the end, it reads fine up to 50lbs. or so, then it becomes erratic, giving higher or lower reading by several lbs. on the same saw.
I put a different gauge on it which read within 2 lbs. of the first one but was still erratic, I changed the schrader with a correct new one to no avail,
So I bought another unit from Design Technolgies, home of the tiny tach, this one pretty much matches the first one up to where that loses it, the new one gives consistent read all the way to 199lbs, I have two saws there.
(edit) 2nd one was $50 & chnge

 

[stihl86]

Use 3 different gauges and cross check each one with your compressor and you will be able to tell which ones are accurate.

How long to take a muffler off. Even one on a MS 200t? 10 minutes? Actually, that was the model that it finally sunk in, after a few other embarrassing episodes, that compression testers on small engines ( except multi cylinder) are close to useless.
Regardless is hose length, valves or a brand.

 

[RED-85-Z51]

How long to take a muffler off. Even one on a MS 200t? 10 minutes? Actually, that was the model that it finally sunk in, after a few other embarrassing episodes, that compression testers on small engines ( except multi cylinder) are close to useless.
Regardless is hose length, valves or a brand.

Pretty much. Even Briggs doesnt bother to publish specs...they say spin it backwards by hand, if it snaps back of the compression, its good enough.

But if you have a saw that..maybe runs okay and the top end is clean but, seems low on power..a compression test can shed some light.

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[old guy]

Useless? comp test tells me just what my mods. have accomplished.

 

[RED-85-Z51]

Stop watch can give you a better idea.

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[old guy]

Stop watch can give you a better idea.

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That tells what's happenin but not exactly why.

 

[lone wolf]

Pretty much. Even Briggs doesnt bother to publish specs...they say spin it backwards by hand, if it snaps back of the compression, its good enough.

But if you have a saw that..maybe runs okay and the top end is clean but, seems low on power..a compression test can shed some light.

Sent from my LM-G820 using Tapatalk

How long to take a muffler off. Even one on a MS 200t? 10 minutes? Actually, that was the model that it finally sunk in, after a few other embarrassing episodes, that compression testers on small engines ( except multi cylinder) are close to useless.
Regardless is hose length, valves or a brand.

Stop watch can give you a better idea.

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Watch is useless .