How do I test compression in MS200T?

[SkipD]

I'd like to know the recommended way to test compression in my MS200T (and in my MS361).

I pulled the plug and screwed in the adaptor and hose for my compression tester and pulled the starter cord a few times. I got up to 120PSI and suspect that I could have read higher pressures but I simply could not pull the cord any harder and felt like the pull cord would break if I tried.

What was I doing wrong or what could I have done differently? With engines having a starter motor, I have done many compression tests over the years (I've worked on cars since about 1962) but this is the first time with an engine having a pull cord to turn it over.

Thanks in advance.

(By the way, the saws both run great. I just felt like doing the measurement.)

Skip

 

[jackjcc]

Does your pressure tester have a schrader valve? Let's compressed air into the tester but not back out.


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[SkipD]

Does your pressure tester have a schrader valve? Let's compressed air into the tester but not back out.

There is a valve, but it does not work quite as you've described.

I can press the little button on the Schrader valve's stem to release the captured gas (normally air, of course) under pressure (in the gauge, hose, and engine cylinder) but the gas does not go through the valve like it does through a tire valve. The Schrader valve is simply Tee'd in to the sample tube to allow the manual release of the captured gas between test cycles. If the Scrader valve actually captured the air in the gauge, you'd never see a leak-down if there were one. When I've hand-cranked my MS200T to 120PSI, for example, the steady pressure I see on the gauge is because there is no leaking in the top end of the saw engine.

My primary question is how to turn over the engine enough to build up the maximum cylinder pressure that it's capable of without wrecking the starting pull cord.

 

[blsnelling]

The valve must be at the very tip of the hose where it threads into the cylinder.

 

[SkipD]

The valve must be at the very tip of the hose where it threads into the cylinder.

I just looked and yes, there is an in-line Schrader valve at the end of the hose (in addition to the pressure release valve I described). I had not seen it because it's in the primary hose that connects to the gauge and my adapter for the correct spark plug thread screws onto the primary hose and hides the Schrader valve. I can see how that valve allows multiple piston cycles to build up the pressure in the gauge.

I now realize that he lack of leaking after multiple piston strokes is because of the Schrader valve near the end of the hose and there could be leakdown past the rings (and possibly elsewhere around the cylinder).

 

[blsnelling]

The adapter must have a schrader valve too. What ever is threaded into the cylinder must have a valve at the very tip. These are small displacement engines and anything in front of the valve adds to the trapped volume, essentially the same has having a much larger combustion chamber. Otherwise, you will get false low readings, such as you are seeing.

 

[SkipD]

The adapter must have a schrader valve too. What ever is threaded into the cylinder must have a valve at the very tip. These are small displacement engines and anything in front of the valve adds to the trapped volume, essentially the same has having a much larger combustion chamber. Otherwise, you will get false low readings, such as you are seeing.

That makes sense.

At the very least, I figure I can take readings now while the saws are performing really well to use as a benchmark for comparison if they start to not run so well. I can easily understand this stuff as I spent 39 years in the industrial process controls business where measurement of things and calibration of the measurement devices is was what I worked with.

 

[2dogs]

Box it up and ship it to Lone Wolf.

 

[lone wolf]

Box it up and ship it to Lone Wolf.

It would be done already!

 

[SkipD]

I don't have any problems with the saw. I simply want to know how to crank the unit enough to get the maximum compression pressure that it would generate. I cannot hold the saw body with one hand and pull the cord very well against the compression with the other. With my age, I am losing some upper body strength so that may be my problem but I also want to avoid over-stressing starter rope or the recoil starter assembly.

 

[lone wolf]

I don't have any problems with the saw. I simply want to know how to crank the unit enough to get the maximum compression pressure that it would generate. I cannot hold the saw body with one hand and pull the cord very well against the compression with the other. With my age, I am losing some upper body strength so that may be my problem but I also want to avoid over-stressing starter rope or the recoil starter assembly.

They get pulled at a good pace until the gauge stops rising. Get a helper if you cant hold it. Why do you need to know the compression anyway? Does it start in 5 pulls or less? Does it run good? Does it stall? Does it cut wood good? Does it hold idle? If it does all these things forgo the compression test.

 

[SkipD]

They get pulled at a good pace until the gauge stops rising. Get a helper if you cant hold it. Why do you need to know the compression anyway? Does it start in 5 pulls or less? Does it run good? Does it stall? Does it cut wood good? Does it hold idle? If it does all these things forgo the compression test.

The only reason I wanted to measure the compression is just for a "benchmark" for the future but mostly for curiosity. I have no complaints about how the saw starts and runs.

Thanks.

 

[Mattyo]

Of all of the chainsaws that I have tested the ms200t is fairly easy to turn over and get a accurate compression test if you are having trouble turning this saw over I think something else is wrong I usually don't have trouble until 200 pounds of compression or more

 

[Mattyo]

8 min mark or so I do comp test 200t

 

[lone wolf]

The only reason I wanted to measure the compression is just for a "benchmark" for the future but mostly for curiosity. I have no complaints about how the saw starts and runs.

Thanks.

Sounds like it is fine . But now I am curious as to the compression numbers?

 

[SkipD]

Bear in mind that I've lost a lot of my upper body strength (almost 70 years old and never was athletic) so trying to hold the saw body and yank the cord on a bench isn't the easiest thing for me. I was able to get to 120PSI pretty quickly and it felt like it would do significantly more if I could pull harder. Even so, I started wondering how much the pull cord can tolerate.

 

[lone wolf]

Bear in mind that I've lost a lot of my upper body strength (almost 70 years old and never was athletic) so trying to hold the saw body and yank the cord on a bench isn't the easiest thing for me. I was able to get to 120PSI pretty quickly and it felt like it would do significantly more if I could pull harder. Even so, I started wondering how much the pull cord can tolerate.

Sounds like it could and will go a lot higher if you keep pulling. Is your tester on a hose about a foot long if so it takes a dozen pulls to get it to stop rising. Dont worry about breaking the pull cord or the parts in there, they break when you pull too far, or if worn.

 

[SkipD]

That's what I was assuming. Thanks for the confirmation.