Slight knocking noise could be pre-ignition, piston play, or a chipped ghear tooth which would have the noise travel up the driveshaft to sound like a powerhead noise.
Pre-ignition would have at lease one spark plug looking pretty weird.
Check the gearlube at the magnet of the drain plug to see if any chips, chunks, or slivers are present. Fuzzy metal fragments that you can rub between you fingers create no problem (normal).
(
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.
Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:
http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
Let us know what you find.
