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I have a (previously working) Honda GX270 engine that I was transporting in my truck recently. The strap came off and it tumbled in the back. Nothing serious, but it was lying on its side for about 15-20 minutes until I could stop and check on it. I can acoustically confirm it did not slam into anything and there is also no visible damage.

So a couple of days later (sitting the right way up) I got some new parts I wanted to install (missing air filter and exhaust muffler, broken tank, nothing inside the engine) and afterwards I wanted to take it for a spin and it was impossible to turn it past the compression stroke. It could be turned back and forth until compression.

I first thought maybe the tumble somehow messed up the valves and it is now pushing against a valve, but they are fine. Eventually I realized when removing the spark plug it turns fine, so it just has high compression. The spark plug was full of oil so it seemed clear what the problem is - oil got into the head and cant be compressed by hand.

I removed the head and indeed there was a good 2-3 teaspoons of oil at the bottom of the piston. I cleaned it out, assembled the head again. It is just slightly better, with a ton of force it can be turned over.

With my limited knowledge I am kind of left with the decompression mechanism as the only culprit left. I find it weird, that this small time on its side would rearrange its guts, but I cant really think of anything else related to the compression.

This is what I am looking for with my question. Are there other things that could cause this or is it most likely related to the decompression? I would really like to avoid opening up the crankcase if possible.

I removed the cam shaft and it looks like the bump that is used to lift the exhaust valve for compression release is somehow ground down:

enter image description here

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If the compression release is not working it seems to me that you have little choice but to open the crankcase and see what's wrong. However . . .

The engine tipped over, so debris such as a metal chip from the bottom of the crankcase could have found its way into the small space between the compression release flyweight and the cam gear, preventing the flyweight from swinging freely.

There's a remote chance that if you drain the oil and add solvent to the crankcase, then jiggle and wiggle and bump the entire engine every which way, the solvent and the swinging action on the flyweight could free the chip from that small space, and that could free the flyweight and your compression release could work again. That's a long shot, but you have nothing to lose but some solvent.

I would use mineral spirits, kerosene or diesel fuel. With a flash point above 100F, all would be safer than gasoline.

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  • Ingenious! Something getting lodged in the mechanism was something I was thinking about but trying to dislodge it like that, brilliant! I will give it a shot tomorrow. Feb 26, 2023 at 20:54
  • I guess I have to bite the bullet and just open it up. Managed to get it running for a couple of seconds and thought maybe that will free it up. However no such luck. Sometimes it is more or less manageable to pull sometimes it is almost impossible. Ill see what it looks like inside :) Feb 28, 2023 at 20:25
  • @YanickSalzmann Bummer! I'd love to know how it turns out and what was affecting the compression release. My money is on a metal chip left over from boring the engine.
    – MTA
    Feb 28, 2023 at 21:08
  • Got some vacation next week, guess I know my project for it, I will add a comment once done :) Feb 28, 2023 at 22:06
  • The compression release is fine and not blocked, however I am not sure if the "bump" it is using to lift the valve is worn out or if it has to look like that. I will order a replacement just in case, cant really think of anything else at the moment Mar 6, 2023 at 15:38
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there is sometimes a small separate 'cap' on the tip of the exhaust valve stem (or its pushrod) that can fall off if the engine flips in the wrong way while the valve is completely closed (or the engine has too much valve lash set) also, some wear is expected (yours doesn't look excessive to me.) and usually the valve can be adjusted to allow the compression release to function properly despite the wear. (this sometimes means also adjusting the intake valve to keep everything in spec )

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