compression test question

[Ray Bennett]

I read some previous post about lifting a saw buy the starter rope as a good compression test. Well I tried it on several saws (all stihls including a new 460)and all slowly went down. All the saws run good and strong. They did all have 20" bars or longer. Should the bar be removed for this test. Im going to a big auction this weekend and need to find out exactly how to do this test and would like to konw if it is really a good way to get a general idea of a saws Compression.

 

[Haywire Haywood]

My guess, and it's just a guess, is that all saws will have some leak down and with the test you're doing, you're looking for it to hit the end of the start rope fast, not slow. Fast indicating low compression not slowing the descent.

Ian

 

[STIHL-KID]

I read some previous post about lifting a saw buy the starter rope as a good compression test. Well I tried it on several saws (all stihls including a new 460)and all slowly went down. All the saws run good and strong. They did all have 20" bars or longer. Should the bar be removed for this test. Im going to a big auction this weekend and need to find out exactly how to do this test and would like to konw if it is really a good way to get a general idea of a saws Compression.

That is what some people do when "field testing" a saws compression. Holding the saw by the cord is a very crude way of getting a definate indication. For me , it has always seemed difficult to do this test on a larger saw with a bigger bar installed. Not sure if this is possible.......but maybe buy a small pocket-size compression tester (rubber tip) style and test what you see if possible. Good luck on saw testing!

 

[West Texas]

It works as a good indicator on my five saws. Not an expert on how well it works for the really big saws. But last month I had a 260 Pro that was performing well; but, about which I was beginning to become doubtful, although things looked fairly good on the inside. It seemed to be sinking a little too quick on the rope test. Having had a new top end kit on hand for over a year, and lots of time on my hands one day; I put it on. Using the starter rope test, it did not initially move when I let it drop, then after a while it gradually eased down. A significant difference noticed. I think its a good field test; on the other hand, a pressure test gauge is pretty cheap and a nice tool to have on hand.

 

[Haywire Haywood]

I like the rubber tipped compression tester idea. My tester is a pain to hook up. I have to use 2 adapters for a total of 4" between the hose end and the plug hole. It's bulky and usually rubs on something getting it screwed in. I also fear that the adapter is throwing my readings off since it spaces the hose's valve off the cylinder.

Ian

 

[joesawer]

Don't trust the starter rope method for auction saws. A badly scored piston will couse a lot of friction and feel very much like compression.

 

[ChuckinOhio]

Don't trust the starter rope method for auction saws. A badly scored piston will couse a lot of friction and feel very much like compression.

That is a very good tip and one that I had not ever considered. Thank you.

Chuck

 

[Crofter]

A couple of squirts of 80 / 90 gear lube in the cylinder will camoflage low compression; unless the saw is freshly run and free of gunk in the cylinder (and not scored) the pull rope test is pretty iffy.

 

[Lakeside53]

Yep... I never use it even as a guide. Been "almost" fooled many times by coatings of old mix oil.

 

[robby26wi]

Just buy a tester ....There like 20-40 bux and well worth the money..

 

[Jacob J.]

The best check is visualizing the piston/cylinder, at least through the exhaust port and spark plug hole. If things look clear, I squirt in some WD-40 or some mixed gas and do the rope check. A lot of times I'm diagnosing a saw on some landing in the middle of nowhere and I don't have a compression gauge handy.

 

[robby26wi]

buy 2 and keep one in your truck lol...just incase

 

[stihltech]

rope test

The rope test is a place to start.Then you need to pull it over and feel if it Spins. This will help distinguish between scoring and low compression.
Would I stop there, absolutely not. If I am spending money on it, it had better run correctly.

 

[JayY]

You can buy a compression tester from harbor freight for $6-$8. They are pretty crude but still a lot more accurate than the stater rope method IMHO. The one I have screws into my saw with no adapters needed and the results compare well to my more expensive model.

 

[royta]

compression test results database

It would be nice to have a list of compression test results, so that users would easily be able to tell if their results are satisfactory.

I received my 044 two days ago and the first thing I did was check compression. I measured 170 psi, and then pulled the muffler to make sure the piston & cylinder wasn't loaded with oil to improve the results.

 

[robby26wi]

170 is very good...anything 150 or better is very good...

 

[royta]

170 is very good...anything 150 or better is very good...

I talked to the previous owner yesterday. It is the original piston & cylinder, and he bought the saw new in 2001. According to the s/n, the saw is a 1998 model. I wonder why the saw kept it's compression for so long?

 

[robby26wi]

lol...i have had saws from the 70's with that compression...It all depends on how they where taken care of...Good fuel and oil,clean air filter and running the carb at the right tune and the compression will live a LONG time...

 

[royta]

lol...i have had saws from the 70's with that compression...It all depends on how they where taken care of...Good fuel and oil,clean air filter and running the carb at the right tune and the compression will live a LONG time...

Regarding carb tune, it sounds like erring on the rich side is the best situation.

 

[robby26wi]

well alot rich or lean is never good but yes a touch rich is way better then lean...