"Before you go to any great ex
"Before you go to any great extent, due to the fact that the knocking may be coming from the lower unit.......
Of course, double check the compression.
(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.
When time permits, visit my store at:
http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
A chipped or missing tooth of a gear will transmit that noise up the drive shaft whereas it will sound like it's coming direct from the powerhead.
If no piston play is evident, remove the lower unit, rig up a hose so that it can be securely connected to the water tube, then run the engine to see if the knocking still exists.
Also (hint) drain the gearcase and inspect for good size metal filings (chips) in the lube and on the drain plug magnet."
