Export thread

Never ran a compression test on this motor before and curious if its within specs. Can anyone tell me the correct procedure? Should engine be tested hot or cold or both? What reading am I looking for to indicate its within spec?? This motor still has a bit of a miss in it and being stored and forgotten in basement for 10-15 years,,,, wondering if the rings rusted away. thanks

the only compression test worth doing is a wet / dry test, hot or cold makes little difference.

The engine has an automatic compression release ( ACR ) and the amount the ACR lowers the compression is dependent upon the valve lash.
Thus there are no figures published.
But because it is an engine you need a minimum of around 65 psi or the air/ fuel / pressure ratio will be so far away from a combustible ratio the engine can not start.

How much comp you got now ????

I kinda agree with Bert having a ACR on your cam but I'm not sure of it..... Storing an engine inside of a house is a good thing... Your rings should be fine.....

Let us know Mon Ami

Yeah thanks both for the info. This genny was stored with no prep...other than emptying gas tank carb in my basement (crawlspace) when it acted up during a power outage. Bought a genny with a Honda motor and just slap forgot about the HM100. Decided to get it back running again...figured out the issue it had during the storm... replaced the plastic gas tank (which had just deteriorated and split).. a new carb, ignition coil, plug, air and fuel filter, and indeed it cranks first or second pull but has an irritating '' poof poof'' backfire/miss and taking a plug reading it comes out greasy looking and dark instead of a nice dry tan. Checked valve clearances and its dead on spec Ahh... hindsight is always 20/20. I could kick myself for not putting some oil in the cylinder and turning engine until valves were closed before storing it. I might pull the head and take a peak... worse case I guess I could get it bored out 10 over while I can still find the parts online... that is if the cylinder walls look scored. O well, something for this old man to piddle with. Again.... thanks for the input.

Notdumasilook said:

Yeah thanks both for the info. This genny was stored with no prep...other than emptying gas tank carb in my basement (crawlspace) when it acted up during a power outage. Bought a genny with a Honda motor and just slap forgot about the HM100. Decided to get it back running again...figured out the issue it had during the storm... replaced the plastic gas tank (which had just deteriorated and split).. a new carb, ignition coil, plug, air and fuel filter, and indeed it cranks first or second pull but has an irritating '' poof poof'' backfire/miss and taking a plug reading it comes out greasy looking and dark instead of a nice dry tan. Checked valve clearances and its dead on spec .

Click to expand...

That "greasy" plug sounds like it's wet with engine oil. Black/dry would be too rich.

Short of a tear down, perhaps soaking some Seafoam in the cylinder @TDC, compression stroke (both valves closed) for a couple days may help.

Rings, oil especially, could be gummed up allowing oil to the top end, thus the nasty spark plug.

I would change the plug in any event..