1971 Johnon 60hp -what should the compression be

[NZ-Kevin]

I've just checked the compression on my engine (which I'd been putting off in case there was a problem). The compression, cold, on the three cylinders was 160, 165, 160psi which is good as they are all similar. But what sort of value should I be looking for?

 

[17rogue70]

Re: 1971 Johnon 60hp -what should the compression be

im no pro ,but that seems to be excellentin my eyes. how many revolutions per cylinder did you allow?should be between 5-7 strokes per cyl.

 

[GeneH]

Re: 1971 Johnon 60hp -what should the compression be

Doing a search before posting will reveal tons of information on compression testing. Your numbers seem a little high but are nice and even. Data is only as good as the test equipment. (garbage in= garbage out) People taching an engine to evaluate a $400 prop make their decisions with $25 tachometers of unknown accuracy. If you know your gauge is accurate, you might consider doing a decarb procedure as slightly high readings can be caused by carbon build up. I certainly wouldn't worry about these numbers. Now if you had 110-30-110, I'd worry. Best of luck!

 

[NZ-Kevin]

Re: 1971 Johnon 60hp -what should the compression be

Thanks for the comments. I spun the engine over for 6 or 7 seconds to get a good reading. I intend doing a full service this winter so may pop the head off then and give it a clean anyway. But all seems OK for now. I'd have been more worried if someone had said the manual quotes 200 for this engine

 

[jay_merrill]

Re: 1971 Johnon 60hp -what should the compression be

Those numbers are about 15 lbs higher than I would expect to see of a '71 J60 (in excellent condition), but that could be compression tester error. If they really are that high, that's excellent!



???

 

[JB]

Re: 1971 Johnon 60hp -what should the compression be

Different people, using different guages, under different conditions and using different technique can get readings varying as much as 50psi from the same engine.

Don't fret about psi. Psi is immaterial. You have a good span and that is what really matters.

 

[phipps]

Re: 1971 Johnon 60hp -what should the compression be

That's awesome! My 71 60hp is 110-110-105, but that is dry. I haven't gotten it running yet.

 

[GeneH]

Re: 1971 Johnon 60hp -what should the compression be

Kevin, do a little searching on decarbing an engine in this forum. Good products are out there which can be fed into the carburetor and which will often remove excess carbon from internal parts. Pulling the head on an older engine with no problems may cause additional problems and may be an unnecessary expense. (The new head gasket, breaking off a head bolt, etc.)