1983 25hp Johnson knocking?

[jpinheiro33]

i just picked up a 1983 25hp Johnson and the thing runs like a top but if you listen you can hear a decent knock. is this normal for these motors or does it maybe have something wrong with it?

 

[CATransplant]

Re: 1983 25hp Johnson knocking?

Knocks are never good. What's a "decent" knock? When does it happen? Does it seem to be at engine rpm speed, or slower.

Hard to diagnose without more information. One thing's certain, though: You need an alternate form of propulsion if you keep running it that way. Something's bound to give.

 

[tx1961whaler]

Re: 1983 25hp Johnson knocking?

Definitely not normal. Usually the knocks quit when the pistons mash the spark plug electrodes closed, though.

 

[GeneH]

Re: 1983 25hp Johnson knocking?

Hi, Have you checked the timing? Any chance your maximum timing advance is too great?

 

[jpinheiro33]

Re: 1983 25hp Johnson knocking?

not advanced timing, the cylinders arent loose bc i tried moving them with a screw driver and the flywheel and they seemed tight. the knocking occurs mostly around a high idle, then when you rev it up a bit it seems to go away. maybe bad piston rings? it does have decent compression when i put my finger over the spark plug hole but i feel and hear a bit of a leak down on each of the cylinders... i could of sworn i heard a 6hp evinrude cruise by me the other day with a knocking to it... something probly justwrong with that too i guess? maybe new rings would fix it?

 

[jbjennings]

Re: 1983 25hp Johnson knocking?

Try turning the flywheel with the s-plugs out and get a piston close to TDC. THen reach in with a screwdriver and hold the flywheel to see if you can push back the piston without the flywheel turning. It's a good way to see if you have a lot of slack in your connecting rods and wrist pins.
Maybe that's your knock. Bad piston rings don't knock as far as I know.
Checking compression with your finger over the hole isn't real accurate.
Why not borrow a compression tester or buy a 20 dollar one from an auto parts store and test it yourself. But if it ran good and idled good I wouldn't worry about compression. Take the cowl off and look for something obvious.
No other ideas, I hope you figure it out,
JBJ