Compression test

[bama]

I got a 2-cycle compression tester from the local parts place and it seemed to work fine on my smaller saws. After rebuild, I was getting about 150 on a Jonsered 451 with a nice piston and new rings + honing.

I tested my 621 today and it showed 200 lbs. after rebuild with good piston and new rings + honing. That just doesn't seem right.

I tested it cold(45 degrees) and pulled it four times. Am I using bad technique, did the tester go bad, should I only pull it once, or is 200 lbs. possible on the 621?

My Remington SL4 with old everything tests at 120 lbs., so I don't know what to think.

There is no point in having a tester if I don't trust it.

 

[rahtreelimbs]

I use an automotive compression tester. The most I ever got on the saws that I tested was 195 lbs. on a modded Husky 372.

 

[retoocs555]

I got a 2-cycle compression tester from the local parts place and it seemed to work fine on my smaller saws. After rebuild, I was getting about 150 on a Jonsered 451 with a nice piston and new rings + honing.

I tested my 621 today and it showed 200 lbs. after rebuild with good piston and new rings + honing. That just doesn't seem right.

I tested it cold(45 degrees) and pulled it four times. Am I using bad technique, did the tester go bad, should I only pull it once, or is 200 lbs. possible on the 621?

My Remington SL4 with old everything tests at 120 lbs., so I don't know what to think.

There is no point in having a tester if I don't trust it.

Sometimes a lot fuel mix in the cylinder can make a nice seal and get you an artificially high reading. 200 isn't so far off that i'd be suspicious.

 

[Kenskip1]

Compression Tester

Bama,Just a quick thought.Was their any oil laying in the cylinder? The reason that I ask is that oil will not compress and could give you a false reading, Ken

 

[bama]

Well, I run 32:1 in my saws so their may be more oil than if I did 50:1. I just ran this saw last week when I was cutting.

If it is oil that is giving me a higher reading, what do I do about it?

Should I test compression after running it?

I just went out and tested a Mall GP and with no scoring, it ran 130 lbs.

Scott, are you saying that it could be close to right or to be skeptical?

 

[SawTroll]

Bama, I just remembered that I made a mistake in one of the pm's I sendt you some time ago - the first 621s had three (not four) rows of holes on the starter cover - in fact my own has it, but it wasn't close to me at the time.....umpkin2:

 

[Dan Forsh]

Without knowing the full in's and out's of this subject (or a cat's arsehole as we say in England) I know others have stressed the importants of the compression gauge being equipped with a shraeder valve for accuracy. As other can give a bogus value.

Maybe this has already been said, but I only read half the posts.

Dan

 

[bama]

Is that the little pressure relief valve that you have to press in order to retest?

 

[retoocs555]

I think your tester is working fine and you just have a saw with a good top end in it.

I generally don't rely on exact numbers from those, but they do give a general idea of condition.

Compression readings are different for EVERY type of saw. The important thing is to have a baseline. For example I know most homelite Super XLs in nice shape have compression around 130psi. Or that new XP huskys in nice shape are usually 160psi. Going on that I know if a saw is above or below average.

Use some scientific method on your 621 to check the validity of the compression reading. Try reading it a dozen times, on different days, at different temps, after cutting, before cutting. See how consistent your reading is.

The schrader valve should be at the end of the gauge, right where it threads into the cylinder. That way you aren't compressing all the air in the hose.

 

[Dan Forsh]

Mine is a crappy thing that I wouldn't buy again, but it does have that. Without experience (he says) I think it's more to do with the positive attachment to the cylinder.

Mine holds the pressure until released, but it just has a rubber head on it, so is reliant on you holding it tight against the plug hole correctly whilst pulling the chord.

Maybe I'm right, maybe I'm not.

 

[RaisedByWolves]

It seems like your certainly in the ballpark with your test.



I like to fire the saw up and warm it up for a minute to clear it out and then do the test.


My 925 reads about 185-190 and sometimes higher (UuugghH) if its not been cleared.

 

[1953greg]

i dont think any compression tester can give a false hi reading unless its calibration is off. goes against all the physics i understand. false lo, yes (leaking). as retoocs said, excess oil can give an artifically hi reading but not a false one. you can tell the difference on the pull rope in a 200psi vs a 165. make some cuts w/ it then test again.

 

[bama]

I will run it for a bit and try it again. I plan to eBay it and I want to be as honest as possible. Not really trying to make money at this, I just reinvest in more saws to work on.

It makes sense that it can't be faulty gauge if the reading is too high. Must be that good or too much oil. I will know this afternoon!

I will start checking my own 621 to get a baseline for reference.


Thanks, guys!

 

[SawTroll]

Bama, the 625II is about the same saw as Husky 61, or even 61 Rancher - not worth the trouble to fix if it isn't OK to start with......

 

[bama]

Bama, the 625II is about the same saw as Husky 61, or even 61 Rancher - not worth the trouble to fix if it isn't OK to start with......

Thanks, Sawtroll. I think it has pretty good compression, but I haven't had time to look at it. Looks good cosmetically. This is the newest saw I have ever owned. I will keep what you said in mind when I look at it.

 

[bama]

Bama, I just remembered that I made a mistake in one of the pm's I sendt you some time ago - the first 621s had three (not four) rows of holes on the starter cover - in fact my own has it, but it wasn't close to me at the time.....umpkin2:

No problem. My first 621 seemed a little different in design compared to the others I have acquired. Good to know that this was on purpose.

 

[bama]

I ran the 621 for about 2 minutes and got it warm. Tested compression and it was 175 lbs. There must have been excess oil in the cylinder that helped give it too high of a test score. Maybe I need to test the compression when the saw is warm???

 

[Lakeside53]

Yes... always run the saw for a while before testing... and if possble cut wood to put it under load and clean it out.

 

[bama]

Yes... always run the saw for a while before testing... and if possble cut wood to put it under load and clean it out.

Sounds good. Thanks, Lakeside.