Chainsaw Compression Tester, Do Adapters Change The Reading?

[David _4]

I'm looking to get a new compression tester and I know there are other threads covering this topic, but I wanted to share a reply I received from an engineer at Lisle Corp.

My question to Lisle,

I'm looking at your 20250 compression tester to use on 2 cycle chainsaws. The question I have relates to using thread adapters. I need to use the 10mm thread adapter for the chainsaws I'm testing, does the use of a thread adapter on a small volume combustion chamber alter the compression reading vs using no adapter. I have been unable to find a reliable answer to this question. Thanks

The reply I received,

David,

Using different adapters does not affect the compression readings. About the only thing to affect pressure readings is to use a longer hose adapter.


Thanks for asking,
Randy Ploeger - Project Engineer

Lisle Corporation
Clarinda, IA

 

[RIDE-RED 350r]

I don't disagree with his reply. And the part about the longer hose just means it might take a couple more pulls to reach peak pressure where the needle stops climbing. Pressure is pressure, it's just a matter of volume and how many revolutions it takes for the piston to reach max achievable compression

 

[huskihl]

It depends on where the Schrader valve is. If there is a valve in the bottom of the adapter, it won't affect the reading. The volume of the hose between the valve and the gauge determines the number of pulls needed to get to max compression

 

[Lightning Performance]

And if the valve is in the top of the hose near the gauge, your reading will be off more as the psi increases. 300 is off 15-20lbs with a two foot hose. Ask me how I know? Not.

 

[smokey7]

Every tester ive used with a adapter showed lower

 

[drf256]

Anything bigger in volume distal to the Schrader valve will add to combustion chamber volume and reduce compression.

Anything proximal will just take more pulls to get to an equilibrium.

 

[Bilge Rat]

Adding an adapter or anything else is another connection/leak.

The O rings at the connections need a very little smear if silacone grease.
Dry and dirty O rings and crud at the sparkplug hole cause most of the false readings that i have seen.

Long and or cheap hoses can bulge/ expand during the pressure pulse changing the pressure a little.
If everything is sealed the next pressure pulse should overcome any low reading unless the hoses are balloons.

With no leaks, a good check valve and the internal volume being constant the readings should be right.

 

[fearofpavement]

I've found that if I use a hose with a longer thread, it gives a higher reading. Never tried a thread adapter, just different thread length hoses and the longer thread reduced the combustion chamber volume resulting in higher readings. Chainsaws have such small combustion chambers that even slight changes can alter readings significantly. I usually don't even check compression on a saw unless I suspect there's an issue.

 

[Bilge Rat]

Anything bigger in volume distal to the Schrader valve will add to combustion chamber volume and reduce compression.

Anything proximal will just take more pulls to get to an equilibrium.[/QUOTE

Dang Doc i had to get my wife to look that up.
I had an idea but had to be sure.

Yep, i agree with that statment.

Grew up next door to a surgeon, lots of big words.
I did retain a collection of Foley and other clamps, forcepts.

 

[old guy]

The adapter must have it's own schrader valve in the bottem or it will give a low reading.

 

[Landmark]

I have never had what I felt to be an accurate reading using adapters...............To figure all this out hurts my brain.

 

[Bilge Rat]

It is a tool.
Try to use it with the same parts and methods.
It only tells you something is wrong or changed drasticly.
Did a test on a little 4 mix hedgetrimmer.
With no adapter 95lbs.
With another hose and adapter 91, 92lbs.
Snap-on tester.
The rings looked good but the tester said bad. The slight piston scuffing told me the tester was right.
It is one tool that combined with other information leads you to the problem.

This motor started out with less than 70lbs After putting new rings in it is above 90 and runs fine now.
The actual numbers are not important , they only show general condition of the motor.

If you want higher readings put a few drops of oil in the top end.

Check you tester against another one to ease your mind about your equipment.
The thing only gives you a clue of the problem.

Ever seen a motor check within spec only to find out after teardown the piston/rings were toast.

We only used the compression tester as a quick test to direct us to dig further.
A leak down is a much better indicator of what is going on.
This was for race cars but a motor is a motor.

Don't rely on one thing/tool to decide what to do.

I am a tool addict, i use a bunch of test equipment but usually they only confirm what i think, see feel what is wrong.

Use everything to test but your best tool is usually your mind.

 

[David _4]

I sent this to OTC Tools,

I'm looking at your 5605 compression tester to use on 2 cycle chainsaws. The question I have relates to using thread adapters. I need to use the 10mm thread adapter for the chainsaws I'm testing, does the use of a thread adapter on a small volume combustion chamber alter the compression reading vs using no adapter. I have been unable to find a reliable answer to this question.

From OTC,

David, No. As long as you keep cylinder volume change to a minimum. Test readings will be true.

Best regards

Jeff S
AA-AS/TSS2.1-NA
Tel. +1 800 533 6127