Johnson LS37 compression

[Mike M]

Hi was trying to find out what compression my LS37 should be giving out.. I’m at 50psi.. I have read that the compression gauges make a difference on the reading .. mine has the relief valve at the gauge and the hose is about 12” any help would be appreciated. Thanks

[Buccaneer]

At that low of compression, if you did get it started, I doubt if it would idle.
Have you had it running before? Are the piston rings free in the grooves?
On most of my little motors, 65 psi is about minimum and still idle
somewhat decent.

Prepare to be boarded!

[Mumbles]

Position of the pressure relief valve doesn’t make any difference in the reading but the position of the check valve does. If the check valve is near the gauge, you’ll get a false reading as the hose will think it is part of the compression chamber in the motor. In other words, the hose will be an extension of the compression chamber, resulting in a low reading. The check valve must be located at the end of the hose or in the fitting which screws into the head. The motor must also be spun over enough times to allow the pressures in the hose and the compression chamber to equalize to get a true reading.

Check valves at the fitting.

1 user thanked author for this post.

Baileydog55

[Mike M]

It has not ran.. sneezing on every 10th pull start.. I haven’t check the piston rings yet. I was hoping that the compression gauge was questionable
Thanks for the help .. going to open her up.

[lloyd]

Compression for that motor should be 70-75 psi cold and dry.

[The Boat House]

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• This reply was modified 3 years, 2 months ago by The Boat House.
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[dave-bernard]

Got to love the 12 gauge shotgun shell. TUBS

[The Boat House]

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• This reply was modified 3 years, 2 months ago by The Boat House.

[Mike M]

Thanks for pics.. I am 2nd guessing to open her up and check piston rings? Should I check out the rings ? Any advice would be helpful I was going to break her down this evening.. thanks

[Mumbles]

Try spraying a bit fogging oil or something into the cylinder and try it again. Laying the motor down first will help to spread it evenly in the cylinder and if the compression comes up noticeably, you can suspect worn rings or cylinder.

1 user thanked author for this post.

Mike M

[Author]

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