1996 Johnson 225HP - Knocking sound

[2250_stratos]

Here is the story. Have not had any real problems so far this year. Its a 1996 Johnson 225 with a newer, used powerhead put on about 3 years ago. Never run it higher then 5000RPM, run reg unleaded all the time with treatment. When she turns on, I get alot of blueish smoke at first, then it cuts back to where you can hardly see any smoke at all, which tells me that I am getting oil in with my gas (it has the VRO system). OK.
The other day I idled out of my canal until I was out of the 5 mph zone, opened it up to about 4500 rpm for no more then 1 minute and a noisy banging noise starting coming from the engine. I pulled back on the throttle to nuetral, and still knocking. Turned around back to the dock. Idled all the way back, didnt want to rev it too high, but it didnt really seem to have lost any power.
With the cover off, it seems the noise is coming from the upper part of the engine, but its almost impossible to zone in on one section. It seems to be right in the middle where i would imagine the crankshaft would be.
My first thought was a bearing problem. Does anyone know how I could go about verifying this before I start pulling anything apart. I would like to be sure I know what the problem is before hand.
ANY suggestions would be a huge help. Cant get back in the water soon enough! Thanks

 

[dcramer]

You're going to have to tear it down to see what's broke. At least you caught it before parts came out the side.

 

[martino1]

I would say a few "Hail Marys" and hope it turns out to be some kind of magnet issue under the flywheel. If it is a rod bearing or wrist pin issue, with some difficulty you can determine that too. Remove all of the spark plugs. On each cylinder turn flywheel until piston hits bottom. Use a long piece of clean metal rod, or similar, and go through the spark plug hole, and use it to place gentle pressure on the top surface of each piston, while gently rocking the flywheel back and forth. The one with excessive "rock" (clearance) has a bearing issue.

 

[joereeves]

(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.