1984 Evinrude 30HP Engine Knock

I have a friend who has a 1984 Evinrude 30hp that runs fine, but has a loud, very noticeable engine knock at high rpm under load. You can't hear it at low rpm. I'm thinking rod bearing. Can it be anything else?

Re: 1984 Evinrude 30HP Engine Knock

That could also be a chipped gear tooth in the lower unit. The sound would travel up the driveshaft to the powerhead. However, do the following procedure... also, is there any metal deposits on either of the spark plugs?

(Piston Play Check)
(J. Reeves)

This procedure will tell you if there is any wear or play in the Wrist Pin, Wrist Pin Bearing, or Connecting Rod to Crankshaft area.

Remove the spark plugs. Insert a screwdriver, dowel, punch, or some object of your choice through the s/plug hole and into the cylinder/piston area. Hold the tool lightly against the top of the piston. Turn the flywheel by hand, bringing the piston up to top dead center, then continue turning the flywheel to pull the piston down about a inch..... all the while holding the tool lightly against the piston top.

Now, at the point whereas the piston has been dropped down about a inch, grab the flywheel and hold it firmly. Now, push that tool solidly and firmly against the piston top.

If the piston moves without moving the flywheel, there is a problem (wear, play, clearance, etc) somewhere with the items mention in the first sentence. Be sure to check all of the pistons/cylinders.

Re: 1984 Evinrude 30HP Engine Knock

Thank you. That's the kind of test/procedure that I was looking for to see for myself if there is any excessive bearing/pin wear.

Re: 1984 Evinrude 30HP Engine Knock

My Johnson 30HP J30ELCUP has a knock also. Only at WOT and not in my regular operating range. I don't know what my RPM's are at WOT, need to check.