Compressin

[Overclock]

We used a leak down test to check on motor health in race cars. A compression test will not show a problem in many cases.
The leak down will show you where a problem is, rings, valves, seals.

Couple it with used oil analysis we are talking a four stroke beast here of course.

 

[Bilge Rat LT 20]

True but ring health is needed on any piston/cylinder arrangement.
It's only a motor, suck, squeeze, fire, and fart, repeat.

 

[angelo c]

What are you trying to do there exactly?

nothing really just a little mental exorcise.

 

[lone wolf]

nothing really just a little mental exorcise.

You working on one now?

 

[angelo c]

LOL - I don't think I have enough experience to answer well, but I'll throw something against the wall anyway....

I think compression readings can be a useful diagnostic tool if you know what a particular saw (or series of saw) reads on a given gauge. Other than that I don't think low speed pressure readings are worth a hill of beans. I don't think the amount of pressure a cylinder can hold at low speeds when cranked by hand is well correlated to what it can do at high speed under combustion conditions.

I also don't think max no load WOT rpm is meaningful other than as a way to set mixture. If it changes it could be a sign of a problem, like any change, but it is likely to be due to many things (like carb problems) beyond compression.

That said, low compression will kill power quickly, so if the saw cannot hold rpm under load (like when it's leaned on), then cylinder pressure may be leaking away. But wouldn't think reduced compression would change no load max rpm in a predictable way - it just doesn't take much to rev no load.

Thanks bud.

 

[angelo c]

You working on one now?

Always working on something....whether at the workbench or just in my head.

 

[Overclock]

It's only a motor, suck, squeeze, fire, and fart, repeat.

Hopefully that'll leave a skidmark.