compression

[high life man]

What is an acceptable figure for compresion? Would it vary by type, size, or age of saw?

About how much is a compression tester, and can anyone reccomend a good one?

 

[Methoss084]

Compression will vary from saw to saw, also with hours of use, wether the operator cleaned his or her air filter often enough, and ran the correct mix. Some of my older saws ie; Disston DO-100 and one of my Lombards requires 2 grown men and a small boy to pull them over LOL. I recently purchased a SUN compression tester kit, and it works nicely, came with a couple different sparkplug adapters and an extra long hose for $75.00.

 

[sonny]

(FREE COMPRESION TESTER )
lay the saw on the floor or ground. Grab the starter rope & lift. If the saw stays down bad compression. If the saw lifts up good compression.

 

[sonny]

it works pretty well, unless the piston is seased.

 

[John in MA]

I have an older Snap-On push-in tester that's great, but someone else has to hold it in when you yank on the cord. The correct figure will vary widely depending on the saw, but one gauge is if it will blow your thumb off the spark plug hole.

And then there are special considerations when testing certain later Pioneer models.

 

[Rotax Robert]

All of these compressiion tests will not give you a correct reading unless you plug the carb venturi with clay and put duct tape over your exhaust, then pull the plug and give a liberal dose of ether (acetelene will do) and put the plug back in....shake the saw for one minute and pull the rope as hard as you can....If the saw dont fire on the first pull, you own a Husky... If it does you own a STIHL !!! It is really that simple...AYE

 

[tony marks]

that test was interesting sonny. no numbers ,but it would tell u what u need to know.later now

 

[Rick Stafford]

From my years of doin saws(????),it's my under standing that ALL engines must have 90-95 psi compression at least to run properly.If you need a man and a boy to start it then you have another problem all together !! Also you should check COLD compression and also HOT. If your readings go down hot,ya got an intrnal problem that needs some lookin into !!

 

[Gypo Logger]

Hi There, Robert has described quite eloquently the Western style of compression testing, however, in the East here we have more class and finesse. The saw is simply held by the starter grip and with gravity pulling on the powerhead, the saw should drop like thick mollasses, but Stihl Madsenized 046's with full Western Wraps and 72" bars will drop as though there were no plug installed.
Another compression test that works equally well and can be done in the woods, is to once again, grab the starter grip, launch the saw from the ground and swing it in a rotational direction upward to over your head, while allowing centrifrugal force to maintain a gentle rotational plane. If the saw can be swung in 2 complete circles before it reaches the end of its rope, then the compression is good, if not a renicosiling of the cyl. may be in order, if a reringing isnt. This lassue style of test is very effective and doubles quite nicely as a means of starting your saw when trying to disperse large crowds of naked logging protesters. This method works well in the chainsaw throw event, however the cyl. should be filled first with petrol.
Madonna was quite taken with it when she first saw me do this with a 357WXPG while I was trying to make "B.C. Tree Free".
Quick Draw McSaw

 

[Walt Galer]

Howdy Highlifeman,

Here is my opinion:

Below 85 psi. Reject - too hard to start. (put a couple drops of oil in the sparkplug hole and you can still get it to run one more time).

100 psi - Action limit. This is telling you that things are not as they should be, such a ring wear or ring wear due to dirt getting through the airfilter. (Sometimes they will come back if you just run the heck out it with some heavy use). Breaking loose a stuck piston, will also result in low compression often, at first, and then with use it MAY come back.

125 - 140 psi. good. Exact value will vary widely with different brands and models. Good idea to check the maintainace manual from the manufacturer, as too much compression indicates heavy build-up on the piston crown or cylinder top, which can lead to preignition/detonation, and destruction of the engine. (Deposits on the cylinder dome can be impossible to see through the ports).

Remember, some engines have an automatic compression release, that makes compression testing impossible with any reliability until defeated.

Regards,
Walt Galer

 

[Methoss084]

LOL! Wether it be scored exhaust side and transfer ports or washed out below the intake port, you just gotta love Rotax Roberts compression test LOL! Hell, don't even bother takin that muffler off for a looksy! LOL!