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 .

 

[stihltech]

Hold it by the starter handle and pull the muffler. Problem solved.

 

[Okie]

Some info I saved from threads on this site about small engine compression testing, schrader valves, their location, types of valves, how to build a SMALL ENGINE compression tester.
Also links to buying a tester that will read correctly with adapters for small CC engines.
I have two know accurate gauges.
If I see a low compression on a small engine I confirm such with my other gauge. I've seen small engine problems blamed on low compression when the run problem was elsewhere.





Link to a video about small engine compression testing6/23

https://www.arboristsite.com/thread...-04&utm_content=daily_newsletter#post-8020777



Here is a link about modding Schrader valves and homemade testers, actron tester, etc

Compression tester issues:

http://www.arboristsite.com/community/threads/compression-tester-issues.310133/



I got 3 of the Napa 700-9556 compression gauge Schrader valves today after the local NAPA ordered from their warehouse. The come 5 in a box and you can buy them each @ approx. $2.20 each. They worked A-ok. One was defective out of it's sealed package, was not spring loaded on back check due to a broken spring, noticed immediately before attempting install for test..





3 /2018
Napa #700 9556 is obsolete.

Here is a special low pressure schrader valve for compression gauges Milton and Lisle part number's and I seen them on flea bay as still available.

Milton 1251-2 @ about $5 each

Lisle 20100 @ about $7



Update info 12/20

Possible good compression gauge for chainsaws at $40, STANDIX 1023

Mentioned at this link 12/20

https://www.arboristsite.com/commun...mpression-gauge-and-tested-a-few-saws.348043/

 

[Automan]

Valve should be at adapter
Valve for this test pops off at 2-5psi-way lower than tyre valve

 

[Bob Hedgecutter]

Seems to be a lot of emphasis on exacting methods when it comes to compression testing and testers.
I for one can not see the need for an exacting number- if its too low- saw wont run, if its too high- well it might hurt your fingers trying to start it.

If you do not have the perfect tester and still want to rely on compression testing- use the tester you have on a known good engine, if the reading is around the same on both- assume they have around the same compression.
For my money, if I was recommending tools needed for someone to work on small 2 stroke engines- a compression tester would be fairly low down on the list.
Having said that, there is one hanging above the workbench- cost about $35 of ours so somewhere between $15-20 USD and have a valve at the plug adapter- still looks like new as I hardly ever use it.

 

[Okie]

Seems to be a lot of emphasis on exacting methods when it comes to compression testing and testers.
I for one can not see the need for an exacting number- if its too low- saw wont run, if its too high- well it might hurt your fingers trying to start it.

If you do not have the perfect tester and still want to rely on compression testing- use the tester you have on a known good engine, if the reading is around the same on both- assume they have around the same compression.
For my money, if I was recommending tools needed for someone to work on small 2 stroke engines- a compression tester would be fairly low down on the list.
Having said that, there is one hanging above the workbench- cost about $35 of ours so somewhere between $15-20 USD and have a valve at the plug adapter- still looks like new as I hardly ever use it.

On a new to me chainsaw I remove the muffler and take a gander at the piston. If it scored badly the engine has severe cancer and is going to need further attention.
I've seen chainsaws have good compression and the piston severely scored.
A good compression reading at first as the only test of the engine does not really indicate that the engine is A-Ok, so I do not immediately go for a compression test. If I see a piston I suspect the saw is running lean or the OIL/gas mix was weak. (piston is overheating for some reason and expanding into the cylinder wall) most generally due to the carb being too lean. To verify a engine overheating I use a IR temp gauge.
A tachometer is also fairly low on my list of tools.
A mityvac vac/pressure tester is troubleshooting tool I use often for engines and carbs.

BUT: as the old saying goes: (this saying gives you a good excuse to buy the tool) Better to have and not need than to need and not have.

 

[Chevboy0167]

https://www.ebay.com/itm/1669493272...1RtUw8BCcbgIfOu8VMLjrPGZkg==|tkp:BFBM_Oqdr5pl

 

[Bill G]

Hold it by the starter handle and pull the muffler. Problem solved.

Not when dealing with FB morons.
They read too much Google

 

[oldguy]

I have two tachs that never get used anymore, but my compression gauge is used a lot.

 

[cdahl383]

I have a cheap Harbor Freight one that seems to work just fine. I also have a Bosch one and they both read within 5psi of each other generally. Both have shrader valves that are right at the tip of the fitting, so maybe that's why I haven't noticed any funny readings.