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Compression check results

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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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Discussion Starter · #2 ·
If I have a blown head gasket, is it a terribly involved process to replace it? I'm assuming that there aren't any touchy things to deal with on a simple little 2-stroke like this since there are no rocker boxes and such.
 

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Discussion Starter · #11 ·
Thanks, Creek Runner.

I'll pull the lower unit drain plug and check there.

The motor sounds absolutely fine at idle (in gear or not). I'm usually pretty sensitive to an off-sounding motor having grown up around two-stroke rental four-wheelers. That's what's been puzzling me. It seems that if it were internal I'd be hearing something at the low RPMs, or it would at least run rough.

The last time I had the boat out I had my wife take the wheel while it was making the grinding noise so that I could listen closely and try to determine the source. I should have pulled the cowling at that time.

It really didn't sound like it was coming from the lower unit, but I'll definitely check and see. Again, I would think it would at least rattle or shift hard at idle if it were a lower unit problem.

I'll keep you all updated. Thanks for the great responses!
 
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