Stihl 020AV Super compression

[PES+]

Could someone post a pic

You have all got me curious as heck.....could someone post a pic of a compression tester that does NOT have a schrader valve?
I have never seen one ........ever
but perhaps this is more new school tooling

as far as the length of the hose making a difference it does not
if you have a longer hose just pull the starter a time or two extra as the last time I checked my air compressor does not drop pressure with a longer hose but has to run a little longer to compress the extra volume of air in the hose

 

[CTPhil]

OK, I'm confused now.

It sounds like either:
the volume of a coupler/adaptor might be enough to show a problem with compression that doesn't exist:

or:
If you pull the starter enough times you'll get a good reading regardless of the schrader valve location...

 

[PES+]

Did not mean to confuse you Phil

You will need to take the saw down and remove the rings.....with any luck you just have worn out rings.

All compression testers have at least one schrader valve or else they would not work at all.

Now that said.....how many times did you pull the saw over with the gauge installed?
and did you remember to hold the throttle wide open when you pulled it over?

 

[CTPhil]

.....how many times did you pull the saw over with the gauge installed?

I pulled until it didn't show any further improvement.

and did you remember to hold the throttle wide open when you pulled it over?

No, does that make a difference?

Also, when I looked into the cylinder through the exhaust port, it almost looked like the rings were rounded at their edges. Is that what worn rings would look like?

 

[PES+]

It can.....you are trying to pump as much air into the cylinder as possible and with the throttle plate closed you are restricting the flow in severely

Try again with the throttle wide open about 6 pulls.....do it several times that way and average what you get

 

[CTPhil]

Try again with the throttle wide open about 6 pulls.....do it several times that way and average what you get

Will do!

 

[kd460]

I would seriously question your compression tester regardless of whether it is the right type or not. See my recent post "low compression after fresh rebuild". This all sounds very familiar to the problem I was having and it was a bad schrader valve in the compression tester.

Get a new one that is for small engines (like the one Bailey's sells) that way you know for sure. The hose and gauge volume is probably more than just a few cc's.

As far as the screw in the gas cap, is the screw on the inside of the cap or the outside? If inside it was for a retaining chain. It does sound like vent problem. If a vent problem, it could cause scoring from runing lean (and then stalling).

I might have missed it, but what does the cylinder/piston look like after removing muffler? KD

 

[CTPhil]

I also may seek a "second opinion" by getting another comp tester.

I tested again, throttle open, lots of pulls and re-test, 110 lbs. was the best I could get.

Looking in exhaust port, everything is smooth and shiny.

The screw in the cap is on the outside and is like a long set screw.

 

[Lakeside53]

I'm not sure if pest clarified this or not...

The location of the schrader valve is very important... Yes, all have at least one, usually near the meter, but the one you need will have one (or more usually an additional valve) at the very tip (no unpumped wasted volume). As I mentioned earlier, any volume between the schrader valve and the cylinder introduces an error. Not important on you big block V8, but a real problem when the dead volume is a decent % of the compressed cylinder volume.

 

[Lakeside53]

as far as the length of the hose making a difference it does not
if you have a longer hose just pull the starter a time or two extra as the last time I checked my air compressor does not drop pressure with a longer hose but has to run a little longer to compress the extra volume of air in the hose

Yes it does... big time, if the valve is not at the screw-in tip. See the preceding post.

 

[PES+]

as far as the length of the hose making a difference it does not
if you have a longer hose just pull the starter a time or two extra as the last time I checked my air compressor does not drop pressure with a longer hose but has to run a little longer to compress the extra volume of air in the hose

Andy...do you get a drop in pressure from your air compressor with a longer hose?

 

[CTPhil]

Well, I ordered a new compression tester from Bailey's. Hopefully I'll be able to get things settled in a few days and move to the next step.

In the meantime, keep the debate going, I'm on the edge of my seat waiting to see how it sorts out.

 

[kd460]

I am doing the same thing, while the new automotive compression tester I bought definetely works, I ordered another one without the quick connect and a shorter length of hose. The scale is also lower (goes to 200 psi), so hopefully accuracy will be better as well.

It would be interesting to find out the differences in values (if any). KD

 

[Lakeside53]

as far as the length of the hose making a difference it does not
if you have a longer hose just pull the starter a time or two extra as the last time I checked my air compressor does not drop pressure with a longer hose but has to run a little longer to compress the extra volume of air in the hose[

Andy...do you get a drop in pressure from your air compressor with a longer hose?

Of course not...

But... you've missed the point. Unless you have a check valve at the tip where it screws in, when the piston goes up, the air in the hose is compressed, and when it goes down, the hose air simply comes back out. Without a tip schrader, the hose ADDS to the combustion volume, but there is no piston on the hose to compress it! With a tip schrader, the hose is pumped up until you release the pressure.


What happen to compression if you have say a compressed CYLINDER volume of 5cc and you decide to add 2.5 cc to it? It's like adding a really thick base gasket!

I have two compresssion guages - one old without a schrader tip and the other with. On an 026 the tip valve version reads reads 155, the the 118. In my truck they both read pretty much the same (not much!).

 

[PES+]

I am trying to tell you that ALL compression gauges HAVE a schrader valve in the plug adapter....if they do not they are the wrong adapter and belong in a leak down tester set.

Can you post a pic of your "old" tester that does not have a schrader in the adapter?

I use my compression tester as a leakdown tester as well....it has a schrader at the fitting below the gauge and I simply unscrew the schrader from the plug adapter and put air in at the gauge schrader

 

[CTPhil]

Can you post a pic of your "old" tester that does not have a schrader in the adapter?

Sorry, I'm not taking sides here, but I have an old tester that does not have a schrader valve in the adaptor. (This is not the one I used for my tests!)

 

[PES+]

That looks very much like a Cal Hawk I had 30 years ago...and the schraders were in the adapters that threaded on to the end shown in your pic..

IE the pic shows just the gauge without adapters

 

[troutfisher]

Of course not...

But... you've missed the point. Unless you have a check valve at the tip where it screws in, when the piston goes up, the air in the hose is compressed, and when it goes down, the hose air simply comes back out. Without a tip schrader, the hose ADDS to the combustion volume, but there is no piston on the hose to compress it! With a tip schrader, the hose is pumped up until you release the pressure.


What happen to compression if you have say a compressed CYLINDER volume of 5cc and you decide to add 2.5 cc to it? It's like adding a really thick base gasket!

I have two compresssion guages - one old without a schrader tip and the other with. On an 026 the tip valve version reads reads 155, the the 118. In my truck they both read pretty much the same (not much!).

I agree, now. It took a while to sink in. It's like having the Spark plug gasket leaking, but only when the piston moves down. thanks Andy!

I looked at a Snap-On tester today, There was a valve at the tip. oil filled guage $210.00, with 2 adapters.

 

[CTPhil]

That looks very much like a Cal Hawk I had 30 years ago...and the schraders were in the adapters that threaded on to the end shown in your pic..

IE the pic shows just the gauge without adapters

It does say "Hawk" on it. But it didn't come with any adapters, just the two-step end permanently attached as shown. I've had it about 35 years.

 

[Lakeside53]

I am trying to tell you that ALL compression gauges HAVE a schrader valve in the plug adapter....if they do not they are the wrong adapter and belong in a leak down tester set.

Can you post a pic of your "old" tester that does not have a schrader in the adapter?

I use my compression tester as a leakdown tester as well....it has a schrader at the fitting below the gauge and I simply unscrew the schrader from the plug adapter and put air in at the gauge schrader

Not so my friend... many don't even have adapters! I beileve my "wrong" tester is a Craftsman for the '80's. Same end as the post above but with a "round dial". It's buried... but I'll look for it.

Then there is the type that have no threads - just a rubber adapter you press into the plug hole.. Luckily they are pretty much impossible to use on a chainsaw that needs pulling over!

About half I see in stores around here, and about half on AS (you can't believe how often this topic come up - do a quick search) don't have the tip schrader... and many adapters are just brass tubes.