Strange misfire type sounds

blue68rs

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Joined
Jun 12, 2017
Messages
2
I have a 87' bayliner with a OMC Cobra 3.0L that is what I thought at first to be misfiring really bad. But upon further inspection I realized that the misfire sound was not entirely a misfire. I had just removed and reinstalled the motor and out drive to replace the shifter cable sleeve. After re-installation of everything, I fired up the boat to perform pre-checks before I water tested it. This is when I noticed that it had a bad misfire, or so I thought. After I removed and inspected the spark plugs and changed the points system, wires, cap and rotor. I then checked the fuel quality and noticed that everything was checking out, so initially I was convinced that the carb needed rebuilding, UNTIL.. Until I leaned on the exhaust elbow, and the misfire sound became exponentially worse. So now I am thinking that the exhaust elbow and the J pipe are randomly making contact, and coincidentally make a misfire sounds as it bangs together.
now the engine was making the same noise before I removed the motor, just more so now, and I can duplicate it at will just by pushing on the exhaust elbow, as well as releaving the noise by puling on the elbow.
So im positive that I have found my culprit, but im not sure how to fix it, or if I can.
My first thought is to removed the exhaust joint bellow and grinding down the J pipe for extra clearance?
Any thoughts?????
Thanks
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,306
welcome aboard

did you align the motor before putting your drive on? if not, the sound you hear is your coupler eating itself
 

blue68rs

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Joined
Jun 12, 2017
Messages
2
I did align it as best that I could, Since I dont have the alignment tool. I used a screwdriver handle that fit inside of the coupler snugly, I pushed it all the way to the back of the coupler, then as the screwdriver rod protruded outward from the coupler through the transom, It appeared to the be dead center.
I also double checked to make sure that the screwdriver handle wasnt loose and able to move, by attempting to move the screwdriver rod, it was solid.
so I believe that the engine and out drive are lined up.
Also when I removed the unit I also checked this before I removed the engine.( sorry, I did not mention this in the original post.)
I did this because I have heard this noise before I tore everything apart, and the engine coupler was complete and looked in good shape when I removed the engine.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
I did align it as best that I could, Since I dont have the alignment tool.
Then you did NOT align the engine. You will be removing the engine again to replace the coupler when it fails.....it's as simple as that.
 
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