chainsaw scored

mmidlam

Member
What are the symptoms of a scored chainsaw cylinder and piston? Hard starting and unable to properly adjust fuel mixture?
 
If you have a saw which starts at all, I doubt the piston is scored.
You could have dirty fuel filter, plugged tank vent, crankcase leak, bad reed(s) (if used), bad carb. box to cylinder connecter if this saw is piston ported, and some carbs have various screens inside. Possible partially plugged exhaust port and/or muffler.

When I used to work on saws, occasionally I could clean up and save a cylinder, and just use a new piston, if some scoring had occurred.
 
We just had a leaf blower do that, got to the point it wouldn't start with priming. took it all apart and found the screws holding the jug to the crankcase had come loose. I put it back together and it started and ran awhile and then died, I think the cylinder/piston may be scored from running with the jug loose. We now have a new Stihl in the shed, SWMBO likes a reliable leaf blower! The old one was a Weed Eater brand and 15 years old, only cost about $60.
 

An overly lean mixture and/or low octane fuel will make the engine more prone to detonation. This can break rings or piston ring lands and cause scoring.
 
Often a saw with a scored wall and piston will start and run after you use starting-fluid. I will also read low compression until you squirt some oil in the plug hole and then read higher. Yank the muffler off and look inside. That is where scoring usually starts.
 
Hello mmidlam,

A couple of screws to get the muffler out, then you will know for sure!

Guido.
 
(quoted from post at 22:27:19 06/16/17) What are the symptoms of a scored chainsaw cylinder and piston? Hard starting and unable to properly adjust fuel mixture?

Sounds more like an air leak, fuel delivery issue.
 
Sounds more like symptoms of ethanol on carb. Have you rebuilt carb lately? Kits are cheap, new gas makes gaskets like cardboard, not soft and flexible, check impulse hose and fuel lines
 
Compression test- put the gauge in, turn the choke off, tie the throttle open and pull the rope until it won't go any higher.
I consider 130 psi the cutoff. much below that and most saws just won't run right, or be difficult or impossible to start when hot because the compression is even lower when hot. (Yeah, I know-your 40 yr. old Homelite can run with only 60 but it has a reed valve in it too.)

Hard starting can be caused by a lot of things: bad or old fuel, fouled sparkplug, hole in the fuel line, hard diaphragms in the carb. plugged fuel filter or plugged screen in the carb. low compression or air leak, like crankcase gasket or crankshaft seals. also broken, loose or cracked pulse hose to the carburetor. probably some other things too.

Difficult to adjust carb: most of the above, but depends on the symptoms. Will it just not rev up like it can't get enough fuel or does the fuel mix go from rich to lean when running?
 
If the saw has been owned or used by an amateur, the most common cause of piston/cylinder failure is no oil in the fuel. Easy rookie mistake, expensive one. If the compression is good, it's not the piston or cylinder. Two-stroke engines are also dependent on compression in the crankcase, which is harder to measure (or feel with the ripcord, if you've any experience). Crankshaft seals harden. The screws holding the crankcase together loosen. The screws holding the cylinder to the crankcase loosen. Gaskets deteriorate. Major leaks=no start. Minor leaks=hard starting, poor or no idle, runs like it's too lean because it is. Cure is pretty much always the same, tear it down and replace the bad parts.
 

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