Engine knock

[CED8ED]

I have an 87 johnson 90hp with what sounds like an engine knock. This is at idle. The cylinder where it sounds like it is coming from has a weak spark(have a new coil on order). Could this be the cause? Any other ideas?

 

[CED8ED]

Re: Engine knock

More info: Used Joe Reeves method for testing piston play and all seems tight. Any suggestions on where to go from here?

 

[jonesg]

Re: Engine knock

compression test it.
autozone has decent guages for less than $30.

 

[kenmyfam]

Re: Engine knock

Switch coils and see if it moves with the coil.

 

[CED8ED]

Re: Engine knock

Compession test was fine

 

[emdsapmgr]

Re: Engine knock

It is good that the compression checks ok. Pull the spark plugs, shine a light in there and see if the knocking cylinder looks like the other three. Once you get all the plugs firing, check the plug tips and see if they all look the same. It is not unusual for upper or lower bearings to go bad if the engine had water in the fuel, or if it was not winterized properly. Pull the plugs out and hand rotate the crank. Listen to any sounds it makes, and if there is any difference between the cylinders. Check for abnormal crank end play as it rotates. You could even pull the side covers off an have a look inside, or the exhaust cover. Both get you a look inside the engine and costs only a few $ for gaskets.

 

[MikDee]

Re: Engine knock

It maybe just piston slap if it's not firing on that cylinder. IMO, Look it over good, but don't do anything till you get the propper spark to that cylinder.

 

[CED8ED]

Re: Engine knock

More info: Got the new coil and still weak spark so I'm guessing power pack. Have to order one of those as well. As far as the knock goes, if I push against the flywheel sharply it seems I have a bit of play. The play only occurs if I push in one specific direction. Any suggestions here?

 

[CED8ED]

Re: Engine knock

Anyone???

 

[jonesg]

Re: Engine knock

that play in the flywheel could just be crankshaft play.
also, you didn't say exactly which direction you push or where on the flywheel.

 

[emdsapmgr]

Re: Engine knock

You may be able to notice a difference in the piston play in each cylinder by removing the plugs and put a pencil through the plug hole to the top of the piston. Hand rotate and notice the pencil movements. Should be the same on all 4 pistons. If one of them does not react the same, you could have an internal problem on that hole. Esp check at top dead center and bottom dead center.

 

[CED8ED]

Re: Engine knock

The play I spoke of is lateral, side to side. My guess would be 1 mm (.04 in) of movement. It seems to only be when pushing in the direction of port rear to starboard front that there is an audible clunk/click. If it is the upper crank bearing, can that assembly be replaced without cracking the case? I did the pencil trick and couldn't see any difference between cylinders.

 

[jonesg]

Re: Engine knock

I don't know if thats excessive end of crank play or not but someone will know here. I suspect crank end play should be barely perceptible.