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I use a chainsaw used for cutting firewood for home heating and recently bought a broken saw with hopes of repairing it as a backup. The saw had very low compression and upon starting would race at dangerously high RPM. I've diagnosed an air leak at one of the crank seals and have ordered parts, including a replacement piston. But I'm questioning whether I should also get a replacement cylinder head.

What is practical advice for determining if a cylinder head can be used or needs replacing? So far I haven't pulled the head for a close inspection, but what I can see through the spark plug hole and exhaust port is that the piston and ring are scored, but the scoring isn't as bad as many examples in photos I've seen (the ring moves and the scoring is visible but doesn't appear deep). Is there a simple test (such as running a fingernail across the cylinder head) to tell if I should replace it?

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  • Pardon the small engine question, Home Improvement seemed like the best site to ask on, although I know it's a bit tangential to the main subject.
    – STW
    Commented Jun 14, 2020 at 19:26
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    I believe mechanics.stackexchange.com is also interested in small engine questions, fwiw.
    – Kevin Reid
    Commented Jun 14, 2020 at 19:35
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    Use a straight edge and feeler gauges to test the head. For the bore test if is out of round - an internal micrometer helps. If you use the old bore with new rings then deglaze the bore.
    – Solar Mike
    Commented Jun 14, 2020 at 19:43
  • Since you bought it knowing it had serious problems and expecting a rebuild, go ahead and tear it down. You'll find what you find; if it's unrepairable into the trash it goes. Commented Jun 14, 2020 at 19:51
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    I’m voting to close this question because it should have been migrated to Motor Vehicle Maintenance & Repair for small engine repair issues.
    – FreeMan
    Commented Dec 20, 2023 at 12:30

1 Answer 1

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Assuming this is a ported 2-stroke engine (you mix the fuel with oil), it has no valves and no moving parts associated with the cylinder head. Nothing touches it during operation. If it is

  1. not cracked
  2. has acceptable spark plug threads and
  3. a flat enough gasket surface to seal then it is fine and can be re-used.

Note that the cylinder (liner) is a different part than the cylinder head. I am afraid that you may be actually asking about the cylinder. If it is scored and has grooves that are deeper than the cross-hatch on the cylinder from the original build, then it would be a good idea to at least re-hone it. If it is more damaged, it may need to be rebored or even replaced. Ask again if you are actually interested in the cylinder instead of the cylinder head.

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  • Does "flat enough" depend on the gasket?
    – Solar Mike
    Commented Dec 20, 2023 at 14:29

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