Engine Knock

[Elund09]

I have a 1980 35 HP Johnson. J35ELCSM. I hear some knocking coming from the engine at all RPM's. The spark plugs are wet and after removing the head, I noticed that the bottom cylinder was really wet ( not sure if it was a mix of water and fuel ) and the gasket looked questionable.

I then pulled the power head and found the upper water guide tube had a half inch gap between itself and the gromet. Allowing water to just spew out instead of being forced thru the engine, even though the tell tale always ran water.

My question is, could this knock be from overheating? Blowing the gasket and pushing water into the cylinder. Or could something else be the cause.

Thanks, Erik

 

[zackhouck]

Re: Engine Knock

Double post.

 

[zackhouck]

Re: Engine Knock

Knocks are when the combustion of the air/fuel mixture in the cylinder starts off correctly, but one or more pockets of air/fuel mixture explode outside of the normal combustion 'area'..which makes the knocking sound.

I could see the heat causing heat soak, which could cause your miss.. & The only way I could see the water causing the knock is by it messing up the combustion, in some way..But in any rate you need to fix that asap, as too not hydro-lock your engine. Cause water in the cylinder, can cause it to lock up.

Thats just my .02 I'm sure some else could help ya out more than I can.

 

[Elund09]

Re: Engine Knock

Thanks for the reply. I will fix the water issue, replace the head gasket and see what happens.

I actually split the block to check the rod bearings too. No signs of dammage/wear. What should I use as a gasket maker in this application?

 

[Beek14]

Re: Engine Knock

Are you sure the "knocking noise" is coming from the powerhead itself?

 

[Elund09]

Re: Engine Knock

Yes, I'm very sure it's coming from the power head. First I thought It was the stator hitting the flywheel. No problems found there after removal.

I will double check this however. Droping the lower unit while I'm at it. I will check the gearcase then.

 

[zackhouck]

Re: Engine Knock

Well as you can see from the number of posts I have, I'm still a noob at boat stuff..but, if it was. my jeep I would try and whatever was on it before. Or look in a manual. But beek brings up a good point..

 

[Elund09]

Re: Engine Knock

Well, aparently I was being paranoid about the engine overheating. After going thru everything I found a faulty spark plug wire, the one for the lower cylinder. I re-did the wires for both cylinders, fired her up and the knock is gone now. Another lesson learned here!! Zack, you were right, just not water like I had described. Thanks.

 

[zackhouck]

Re: Engine Knock

Hey man no worries I'm glad to hear you got it running! I wish I had the same success as you! Lol