Knocking noise, now what?....

[Jace817boater]

First off, 1989 Evinrude 150XP, premixed 50:1.

And now the story. I had finally gotten the right prop for the boat and was taking it for a cruise turning a nice 5000-5200 RMP at the time and running great. All of the sudden, there might have been a slight pop and then it start knocking and running poorly. I immediately shut it down. Gave it a few minutes and tried to start.

It was obviously still missing and there was a loud knock. I pointed the trolling motor to home and called it a day. When I got home and opened the cover I was I was relieved to find a loose spart plug (middle port side). I took it out and found it to have a light colored coating, brushed it off and put it back in. Started up this time easily, but still the knock. Only ran it for 3-4 seconds not wanting to damage anything. I pulled the rest of the plugs for grins and all but the middle starboard were wet and oily. The middle starboard was drier than the rest, but no gray residue like on the other side.

I know the first the I need to do is a compression test, so I will be picking up a gauge tomorrow. In the mean time, anything else I need to be checking? Since both middle plugs looked dry, is there a possibility of a clogged middle carb and thus no gas/oil and not good...? Since it is premixed, shouldn't it have quit running before doing damage?

I will hopefully be able to update with compression readings tomorrow. If the compression readings look good, do I crank it up again and let it idle and try to figure out where the knocking is?

Thanks in advance.
Jason

 

[Joe Reeves]

Re: Knocking noise, now what?....

(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 (copy/paste) at: stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store

 

[emdsapmgr]

Re: Knocking noise, now what?....

The dry plug on the starboard side could indicate a fuel delivery problem from the center carb. You might want to disassemble it and check the jets on on the starboard side. If you have a plugged or clogged jet, it would not flow fuel properly. Insufficient fuel and oil on one cylinder could cause it to overheat and abnormally expand in the cylinder. If the starboard center was run with poor fuel/lubrication, check that hole specifically for piston scuffing.

 

[F_R]

Re: Knocking noise, now what?....

Quote "Since both middle plugs looked dry, is there a possibility of a clogged middle carb and thus no gas/oil and not good...? Since it is premixed, shouldn't it have quit running before doing damage? "

Yes, clogged carb will starve its' associated cylinders from gas/oil/lube. No, it will not quit running before doing damage. Slow down, maybe. Once it's bad enough to quit running, it's all over.

 

[Jace817boater]

Re: Knocking noise, now what?....

Joe, thanks for the procedure. I will do this tonight when I check the compression.

I agree that there seems to be some things pointing at the carbs. It was exactly a year ago that they were rebuilt, but something could have gotten in there I'm sure. Hopefully it won't be toast since I got it shut down within the first few seconds.

 

[Jace817boater]

Re: Knocking noise, now what?....

Well bad news. Compression readings show (left to right, top to bottom) 94, 95, 0, 90, 90, 91. After finding the 0, I put a screwdrive in it and turned the flywheel and no movement. Does this mean the cylinder rod is toast?

I have the shop manual, and consider myself mechanically inclined when it comes to carb rebuilds and such, but I have never gone inside so to speak. Is this to be attempted? How much $$$ are we looking at for the shop route? Is it worth repairing or do I look to repower?

 

[Joe Reeves]

Re: Knocking noise, now what?....

The "0" compresion and no piston movement means that the connecting rod/piston is no longer connected to the crankshaft. Now is the time to remove the cylinder heads to inspect the pistons, cylinder walls, etc.

For reference, standing in back of the engine, facing the spark plugs, the cylinders are number as follows:

2.....1

4.....3

6.....5

As it stands, it doesn't really matter what you do, tear it down, whatever as the powerhead will either require rebuilding or replacing.