Compression release

[mgsolakis]

Would a compression relief valve interfere with taking an accurate compression test?

[fleetwin]

Yes, the compression relief would affect compression readings if the engine is hand cranked for the test. No effect if the electric start is used for the compression test.

[Tom]

What kind of motor… Manual release lever (early Johnson) or electric start 50’s style?

T

[mgsolakis]

Son of a gun. Yes it is a late 50s lark motor. This is a side note but would an automotive solenoid work on this motor. I have the wiring harness and a push button start as well as the choke solenoid and a battery. But I don’t have a solenoid. I thought the motor was junk due to low compression but it seems I may have been wrong.

[frankr]

An automotive solenoid (Ford) looks identical, but is different inside. If you try to use it, you will instantly destroy the starter safety switch. Yeah, yeah, I know. You can make it work if you know how, but you will lose the safety function, and be responsible for a serious accident if somebody gets drowned or ran over.

[mgsolakis]

Well that sounds like a bad idea. I want that function but not at the cost of risking hurting anyone.

[dan-in-tn]

Frank, Im all for safety, but you don’t even need the starter solenoid to take compression using the starter with a standard jump switch. Don the valves in the head can be bad even if the compression release is not activated during electric starting. Just some things the trouble shooter should take into consideration before junking a potential good engine. The valves in the head can be checked and repaired just like valves in a 4 stroke or another head can be found. I know you guys know this, maybe you just didn’t want to go that far at this time?

Dan in TN

[frankr]

All is true.

[fleetwin]

Have often wondered about those silly valves wearing out, never had much experience with them though. I’m thinking the compression gage could be used to isolate bad valves, at least on an electric start engine. Do the compression test with the recoil start, then do it again with the electric start. Valve problems might be indicated if readings don’t increase dramatically using the electric start.

[mgsolakis]

My issue is that I can’t use the electric start without a solenoid. So there is no way to accurately test compression. Plus I was hoping that an automotive solenoid might help me get the electric start working. But that seems like a bad idea as well by the sounds of it.

[Author]

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