Compresstion Test

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lumberinspector

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What is the proper way to check compression on saw?

I have heard some guys using a compression tester, leak down test. Is there a compression tester made for small engines?

Thanks
 
Any compression tester that has the schrader valve in the tip (where it screws into the plug hole) will work. I like a warm engine that has just run to make sure of no false reading with oil buildup, but it really doesn't matter for the usual diagnostics. Just pull it over normally until the gauge stops rising, 3-8 times usually depending on the gauge tube length and saw size.
 
On a Stihl (of the past 15 years) I see 170-180 after a couple of hours of run time, 150-160 for most of their life, and then a gradual die off to 145 or below. At 135 it's pretty bad, and at 125 or so they are pigs to start, somewhere around 110 they won't start at all.
 
Lakeside, can you recommend a small engine compression tester that has the schraeder valve in the tip? One that works well. A particular brand name perhaps? Thanks...Mark
 
I got mine at car quest.. no idea of the "brand". It's really easy to see the valve... Be careful of adapters etc also. Add a few cc of volume before the valve and you get low readings , particularly on small saws.
 
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Lakeside53 said:
Any compression tester that has the schrader valve in the tip (where it screws into the plug hole) will work. I like a warm engine that has just run to make sure of no false reading with oil buildup, but it really doesn't matter for the usual diagnostics. Just pull it over normally until the gauge stops rising, 3-8 times usually depending on the gauge tube length and saw size.


exactly.........
 
359 Clutch Removal Tool

Can anyone tell me where to find a clutch removal tool for my 359? Do you also recommend using a piston stop tool. Im wanting to replace my rim and bearing.
 
vapnut257 said:
Can anyone tell me where to find a clutch removal tool for my 359? Do you also recommend using a piston stop tool. Im wanting to replace my rim and bearing.
The Husqvarna part # is 502-52-22-02. You can order one from any Husky dealer. It is essentially a socket with three projects on it to engage the clutch with a handle welded on the back side of it. The clutch has left-handed threads on it. Metal piston stops are generally not looked on very favorably here. A favorite of many is to remove the spark plug and insert a piece of rope down into the cylinder. The object being to stop the movement of the piston when the crank is rotated and the piston can not travel any further after it mashes into the rope. Do a search on this technique to learn a lot more details because you can have problems with it also. I like using an impact wrench to remove clutches. The Husky tool would require modifications to use it like this. You can grease the rim drive bearing through the hole drilled in the end of the crank shaft with your grease gun. The only thing you would have to remove is the clutch cover in order to do so.:chainsaw:
 
Lakeside53 said:
I got mine at car quest.. no idea of the "brand". It's really easy to see the valve... Be careful of adapters etc also. Add a few cc of volume before the valve and you get low readings , particularly on small saws.
Will those testers with hoses produce lower readings ?
 
The hose doesn't matter if it has a schrader valve at the plug end tip. If it doesn't, the readings will be lower, and can be very low on a small saw.
 
Thanks guys

Am I correct to assume those numbers are the same for say an 025 to an 066?

Is there a place other than the saw shop to find values of used saws? Say something along the lines of a used vehicle book only for saws? Also are you able to get your hands on service/repair manuals for Stihl?
 
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The numbers are roughly the same across most Stihls of the past 10 years. You can get service manuals though your dealer, or, maybe someone can email them to you.

As for use saw prices... nothing official, and it's seasonal, but the best bet is to carerfully watch Ebay and Craigslist.
 
Well, let's stir things up a bit. When working on a 4 stroke, in most cases the manufacturer will give a spec for what compression should be, and if it is low, a leak down tester can be used to verify where the leak is, say a valve or head gasket, or rings. When working on a multi-cylinder engine, you should not see more than 5 or 10 % variance from one cylinder to the rest when checking compression, regardless of the actual number.
So why don't the 2 stroke folks publish compression specs? I talked to a STIHL engineer, and was told that compression readings don't necessarily have a lot of value, and that is why they don't advocate doing compression tests. I have seen an engine that had good compression when the rope was pulled through, and showed well over a 100PSI on a gauge, but the engine wouldn't run. I pulled the jug and the intake side if the piston skirt was extremely worn down from water scoring, and actually had a small chunk missing at the bottom, so this engine couldn't build any primary compression in the crankcase, and therefore there was no flow when the transfer ports opened, and the engine would not run. So that is one example of where the compression test was of no value. Depending on what part of the piston is damaged, you could have good compression but no start. I am not saying don't do it, but just be aware that good compression may not mean everything is OK in the engine. For small saws and trimmers, they should hold their own weight by the starter handle, as a rough quick check, but beyond that pulling the muffler and maybe the carb on a piston ported engine and looking in with a light tells me more than using a guage does.
Also, gauges vary alot. I had the chance to test 6 KD compression gauges at once and on the #1 cylinder of my truck they all gave a different reading by as much as 10 pounds, and I figured these were decent quality.
All I work on is STIHL, so does Husky or Dolmar or anyone else actually publish compression specs?
 
How much is "well over"?

You mentioned well over 100 PSI but chances are the example you post would not start because the compression was too low. The chunk out of the piston would have to be pretty large to keep the saw from at least popping. piston port saws are quite leaky in their scavenge by design.The ring is what does the sealing work.
 

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