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Compression check results

2631 Views 12 Replies 5 Participants Last post by  fsae99
Hey gurus!

My 2005 30 hp Johnson 2-stroke with electric start was making a strange grinding/clanging sound at high RPM or in the mid-range under load (plowing or turning while trying to get on plane).

I did a compression test today and got an equal 90 psi in both cylinders. I was expecting to get closer to 100, but they're both equal and it doesn't seem terribly low.

My owner's manual says nothing about cylinder compression.

How do these numbers sound?

BTW, when I pulled the cowling cover off I noticed that the starter pinion was engaged. It is showing a small amount of rust in the gear teeth. If this is not disengaging after the motor starts, I'm thinking it could be the culprit.
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#1 I'm glad you did a compression check 1st!!!

#2 90lbs is low for that engine, that's a pretty high compression motor 110+ seen some as hish as 130.

# I don't think that is your problem though, 90lbs on both cyc. (assuming that's what it is, maybe higher if you were to use a better gauage if you used a cheap $20 guage) Nor do I think you have a blown head gasket, it doesn't cause a grinding noise. But to answer your question it's pretty straight forward to change on your engine.

How does the motor sound at idle? How does it sound on the hose? Pull the cowling and rev it up in netural by the carb? Pull the oil drain plug in the LU and see if you have metal frags.

That motor should not have the starter engaged when not running, Put some grease on the bindex shaft and work it up and down by hand,

Geeze that sounds kind of ----- :D but you get the point
 

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Was that CC done with throttle open or closed? My Johnson manual say to preform CC with throttle WFO. Just for grins, I did CC on mine a while back and there was 25PSI difference between throttle WFO and closed.
Is that your version of WOT, wide f------ open (WFO)! LMAO :D Never seen WFO before but I like it!

That engine should not be done with the butterfly open.
 
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