Compression tester issues?

[TheTone]

Where is a source for low pressure Schrader valves? (or can a low pressure one made using a standard Schrader valve core)
and
Why do you want the plunger of the Schrader valve to stick out of the housing below the spark plug and into the cylinder?(if you have a compression release plunger on the output side towards the gauge))

I got the Schrader valves on ebay or amazon, don't remember which - 3 of them for about $5. I leave the threaded valve tube extending about 1/16" or less and have the valve itself right at the top so my tire valve tool can reach it to take it in and out. Having the stem sticking out makes it easy to release the pressure when finished or doing another saw. I don't have a release valve - a piece of rubber fuel hose connects the adapter either to a Mityvac or the stem of my compression tester depending on the situation. Never have had occasion to get another compression tester because my old Craftsman has been spot-on accurate for 45 years.

 

[jmssaws]

How you pull the saw over will change your results.

If you get nasty and fast it will show more

Check the same saw 10 times and you will get 10 different results.

Temperature and humidity and residual oil all change it

 

[twinstaged]

I always have to put a little extra snug with the tester to compress the o ring on mine or I get wonky readings. It's just like any other tool that may or may not be calibrated, but you can still use it for comparison if you change something with the motor.

 

[Okie]

Yes sir, I do ALWAYS looks at piston and cylinders to "assess" the saws health...the piston can tell you a lot about the saw...

I will say that I am by NO means saying you shouldn't use a compression tester, I am just saying sometimes all is well even if you get a low reading....

Good luck and let us know how the saw runs...

Right:

Hope the tone comes back and answers my 2 questions in the above post about his compression tester mods?

 

[TheTone]

Right:

Hope the tone comes back and answers my 2 questions in the above post about his compression tester mods?

Done deal. Check a couple of posts up.

 

[torch]

Where is a source for low pressure Schrader valves?

Snap-on part number MT24DB1 is a set of 3 cores only.

Alternatively, steal the core out of a snifter valve (for a bladderless cushion tank, find them in the well pump section of the hardware store). But you'll pay as much for one complete snifter valve as for 3 Snap-on cores.

 

[Rockjock]

Snap-on part number MT24DB1 is a set of 3 cores only.

Alternatively, steal the core out of a snifter valve (for a bladderless cushion tank, find them in the well pump section of the hardware store). But you'll pay as much for one complete snifter valve as for 3 Snap-on cores.

They are not that much $$$ from snap on or mac. The guy in the truck hands them out when we ask. Then again the gents in the shop have spent crazy money over the years!

 

[Okie]

I made some of the low pressure Schrader valves today that work great.

I got time toady to play with the compression tester design that the TheTone posted.

I had some of the 2 inch long automotive valve stems, ground off the rubber to the brass stems in a wire wheel bench grinder, epoxied the brass stem into a Homelite EZ spark plug and tested with a regular Schrader valve and reading was like 50 psi max and my actron tester read 125. Did not have to add the copper tubing to the stem per TheTone's design.
I have some of the long automotive Schrader valve cores that you can see the little spring so I took one of the long automotive Schrader valves (about 1 inch long and you can see the little spring that has about 10 turns. I used a o ring pick and pulled the spring out from the stem and cut off about 3-4 turns so as to weaken the valve and used the o ring pick to pull the disguarded end out enough so as it could be pulled off with needle nose pliers (could probably have been just threaded down (turned down) into the other spring) and the homemade tester then read 150 psi. I cut another and tested as A ok to make sure it was not a fluke. I removed the low pressure valve from the actron and installed it in the homemade tester and the reading was 100 psi. I'm going to play with the actron tomorrow with the homemade low pressure Schrader valves and see if I can get it too read as high as the homemade tester.

I shot some WD40 thru the muffler port with the piston down and the compression went from 150 to almost 200.
This is on a good running old Homelite EZ.

After you have cut the spring you can feel the weaker valve action with your finger or a pin punch AFTER it's installed.
Bottom line: The Schrader valves have a large impact on the compression reading and the valve spring needs just enough spring action for a good seat to hold the max compression expected so as it don't leak back and open good on the compression stroke for a high gauge reading..

 

[TheTone]

That's a very graphic demonstration of how valve opening pressure affects readings! Yes, there are other things that cause variation also, but if you can keep your tester true and your technique consistent, that reading can be a helpful part of your evaluation.

 

[Rockjock]

Okie I think you took a very simple fix and made it into an exercise of futility.
Wrong one.

The right one.

Any garage would sell you the proper one for a buck or 2 and you would be sure of consistent results. I am all for make work projects when they are warranted but this.....

 

[Okie]

, home schoolingRockjock: (just now noticed you are the guy that said you get the low pressure Schraders from the snap on guy)
My son see's the Snap on man at his work place every once in awhile, I'll have him ask the snap on guy about their compression Schrader valves with the white band and I'll check with the local tire repair shop in town. (doubtful that the local tire shop knows their is a difference in the valves, Gomer and Goober are the garage tire repair guys and as you can tell they were also my school teachers, home schooling )

Are the Schrader valves color coded as for pressures or ?
I was not paying any attention to the band color on the valves but did notice that I tried tried the Red, Black, Green banded ones and all produced lower reading than my modded long external spring ones but have never seen the white band and I searched for low pressure Schrader valves on line and came up blank.

The Schrader valve that I tried from my actron 2 cycle tester has a green color band. (it also gave a lower reading than my modded ones)

 

[Okie]

That's a very graphic demonstration of how valve opening pressure affects readings! Yes, there are other things that cause variation also, but if you can keep your tester true and your technique consistent, that reading can be a helpful part of your evaluation.

Very true. I have 3 compression testers and all 3 will give a different reading on small cc chainsaws. The actron reads highest using it's OEM green band Schrader valve and 1 foot long hose until I started playing around with the modded Schrader valves and I used a very short connection to the spark plug adapter for the gauge with the Schrader in the cylinder per your design.
The gauge has a release valve.
I'll see if I can find one of the white banded Schrader valves for a test run later.

Also the saw I was playing with was removed from being stored, tested cold and the cylinder when I looked thru the exhaust port the cylinder and piston was completely dry and when I gave it a shot of WD 40 the reading went from 150 to close to 200. Next time I'm testing I'll compare test the reading after the saw had been run and warmed up.


Another post about a guy struggling with his compression tester telling a fibb.
http://www.arboristsite.com/community/threads/chainsaw-compression-testing.163538/

 

[a. palmer jr.]

The fewer adapters you use the better..

 

[Okie]

The fewer adapters you use the better..

I'm going to test the spark plug adapter next with no adapters/couplings after I dig out 0-250psi gauge and hose barb just too see if any loss in the couplings, but I'm doubtful that I will gain much since the Actron with the 1 ft long hose and adapters reads about same as th real short connected homemade tester.
My homemade gauge now reads little bit higher than the store bought Actron CP7828A and the gauge reaches max with less pulls of the rope.

I noticed that the actron 7828 OEM Schrader valves will not fit into a standard automotive valve stem and vice versa.
(Their body and threads are different)
I did not know of different body types of Schrader valves???(might be a foreign design, metric or china one of a kind)

I found some of the long automotive type Schrader valves in my valve core catch all box that have a smaller more wimpy external spring that is easier to cut and mod as compared to the black band ones with the stronger spring mentioned previously. (I have probably about 1000 loose valve cores, caps, etc in a plastic box by the tire changer)

 

[TheTone]

To summarize: If your valve is at the end of a "pass through" hose it will never reach true compression because the hose increases volume in the system thus lowering pressure. If you have a long hose after the valve, it will asymtotically approach true compression - from a practical standpoint, this only means it may take a few more pulls before the needle stops climbing. Somehow PV=nRT comes to mind from distant past.

 

[Okie]

To summarize: If your valve is at the end of a "pass through" hose it will never reach true compression because the hose increases volume in the system thus lowering pressure. If you have a long hose after the valve, it will asymtotically approach true compression - from a practical standpoint, this only means it may take a few more pulls before the needle stops climbing. Somehow PV=nRT comes to mind from distant past.

I dug out a 0-300 gauge, Air line male/female quick couple, inline Tee for compression release, short 3/16 hose and kept everything as short as possible and reading still good as the same as before.
Homemade gauge indicates slightly higher readings that the Actron and responds faster, with less pulls of the rope. The 028 compression did not increase as much as the EZ when WD40 added to the cylinder and the 028 compression went down little bit with a warm engine.

This 028 and the EZ both are over 30 years old, not pretty to look at, been used a lot but not abused using Stihl bar lube and Stihl gas/oil mix. (and only one operator, me) Both saws have had one carb kit and fuel lines over the years. Still have the OEM spark plugs and bars.
I run the saws carb dry before storage and they are used for about 3 months each fall/winter.
Appears these two saws may outlive me if I can keep bro in law from touching them.
I have other saws that are nicer looking, and not very old, but these two are my old go to dogs that just keep on running like the energizer bunny.

 

[TheTone]

Appears these two saws may outlive me if I can keep bro in law from touching them.

If I loan a saw it comes with a tank of mix. "This is what you use for fuel". I know from experience how easy it is to straight gas a saw if you grab the wrong gas can. You don't have to be clueless to make a bad mistake. Mindfulness is essential in ALL aspects of sawing (and life).

 

[Okie]

If I loan a saw it comes with a tank of mix. "This is what you use for fuel". I know from experience how easy it is to straight gas a saw if you grab the wrong gas can. You don't have to be clueless to make a bad mistake. Mindfulness is essential in ALL aspects of sawing (and life).

AND
PV=nRT

I do not use or rely on compression testing very often on chainsaws probably mainly due to not getting repeatable readings and not trusting the Actron gauge when used on chainsaws. I now have a backup tester that I can use if I see very low readings from a saw, I can now confirm with another tester. If a saw is weak or erratic I do a crankcase pressure/vac test first usually, especially on old saws.
I use a leak down tester that I built and mainly use it on small 4 cycle engines that been donated to me to get an idea of their internal cylinder piston/ring condition before attempting a repair, just to see if they are maybe worth repairing.

Have a nice memorial weekend and thanks for the compression tester tips.

 

[TheTone]

Same to you . . . and all!

 

[LegDeLimber]

I found these cores at a nearby NAPA. part# 700-9556 (quantity of 5)

Just for giggles and comparison, I once tried the core from a (Chinese) wheelbarrow tube.
IF memory serves me, It cut the compression reading by nearly half!