saw compression

[crowe]

Hello,
I was wondering what would be considered good compression on a saw. I was curious what a new 372 should be holding as far as compression is concerned. I just picked up a lisle compression tester yesterday I went down to the barn and checked the compression on my 372 I pulled three times, it carried 165 lbs I have had it now for around 6 months and have probably cut a little over 600,000 ft with it does that sound pretty good? let me know what you guys think, Wade

 

[Whistler]

IMHO , you broke it in right , remember how you did it !

 

[John in MA]

165 is fine. I'd be surprised if you could get any more out of an even slightly-used saw. A couple of my old Homelites will run that, but the rest I have go as lot as 120 (big-bore Jonsey).

 

[bwalker]

Also keep in mind the correct number varries by model. Some twos troke will run as high as 200 while other are just over 100. Depends on the height of the exhaust port?

 

[Whistler]

I have a couple 'cord breakin' 80 jonses that still go over 200 ! I usually pull the plug and choke em for 4 or 5 pulls and then start em up . Too painful otherwise !

 

[treeclimber165]

Also, gauges can vary on accuracy. Even name-brand models. Remember that guy a few months ago that freaked out cause his saw was only showing 125 lbs compression? He tested every weedwhacker and blower in a two-block radius, testing all his neighbor's equipment, and couldn't find a single engine that tested over 130. He ignored my suggestion to just try another gauge, or simply accept that his saw had good compression.

 

[Whistler]

I just re-ringed a jonsered 70E that was down to 130 . Put it back together and it would start at idle , choke on , but when I took choke off , it died . I tried everything posible to figger out what I did wrong and finally got it . Any guesses ?

 

[John in MA]

Assuming the carb and fuel lines were gone through, I would guess either broken bakelite carb spacer or loose cylinder. Even close?

 

[Whistler]

John, I'm gonna have to give you that one as I didn't go through the carb until the problem arose . When I blew out the carb area prior to dissecting , I must have gotten too much bug-dust in the metering diaphram area of the carb . Cleaned it out and replaced the diaphram and presto . I determined this after I took everything apart assuming it was a gasket I put in wrong . Not ! Good job John ! Jon

 

[daveb]

compression gauges

The fact that comprssion gauges vary in accuracy, leads to the fact that they are more usefull in multi cylinder engines to check or verify consistancy or variation in the readings between cylinders, rather than the actual number. The tool that I have found to be indespensable is my Snap-on cylinder leakage detector. 10 times more usefull than a compression gauge. I never tried it on a two stroke, but it tells volumes about an engines condition in short amount of time.

 

[dbabcock]

Leakdown is the only reliable test for ring sealing in a 2 stroke. As Ben says, port timing has a lot to do with absolute vs. effective compression ratios. Absolute compression readings for a two stroke cylinder, while not meanless, don't tell the whole story. If the motor has more than one cylinder, then relative compression readings can indicate a problem.