4 cyl push rod bent

[knied1]

I have a 3.7l Mercruiser, whren i bought the boat i fired it up and there was a loud knocking, i had a good spare motor, so i swaped them out. Now i was lookiing to see what was wrong with the first motor, and found a bent push rod. I would like to fix this motor for the just in case factor. What should i look for to find the cause of the bent rod? I dont want to just throw a new rod in, and bend it right away. hopefully i never need the motor, but i just want some insurance.

any help, and or sugestions on what i can upgrade would be great.

 

[Howard Sterndrive]

Re: 4 cyl push rod bent

it's possible your motor hydrolocked from a bad exhaust manifold/riser.
If the same manifold went on your replacement motor you better investigate.

1 bent pushrod is generally not the cause of "loud knocking", but pushrod more of a victim of the knock... like failed rod bearing (piston hits valve and drives valve and pushrod shut bending pushrod)

For other possible causes, here's a good primer- the section on valve problems is excellent general info:
http://www.aa1car.com/library/ar1192.htm

 

[Don S]

Re: 4 cyl push rod bent

Stuck valve, broken valve, bad timing chain, who knows. It's out of the boat, pull the head and timing cover and check it out.

 

[TilliamWe]

Re: 4 cyl push rod bent

Yep, the one 3.7l that my dad worked on for a friend had a bent pushrod on the rear cylinder. It was due to the exhaust manifold/riser/gasket failing allowing water to get in that cylinder. I sure hope you didn't use the old exhaust manifold/riser on your replacement engine.
Of course it could be other things, as Don mentions.

 

[knied1]

Re: 4 cyl push rod bent

I ran all last year on the motor that is currently in my boat and no problems,
But yes I did do a complete swap, motor and everything attached, outdrive, and gymball housing, the spare stuff I had was simply in better shape, and figured since I was into it, I may as well.

I am currently taking the 4 bl carb from the motor in the garage, and putting it on the motor in the boat (I have a separate thread for that one)

When I fired the motor up last year, I just assumed that one of the cylinders were shot, (due to the noise) and immediately swapped it with very good strong running equipment. Its just been sitting in the garage for the past year, and since im pulling the 2bl off the boat, and puting the 4bl on, I figured it would be a good time to take a better look at the motor. When i pulled the intake manifold off is how i found the bent rod.

One more thing is that the outdrive didn?t have oil in it, and internal parts have surface rust could the extra drag from that be the cause?

My plan is to go thru the motor and be shure all parts are good, just so you know im not looking for the magic answer, im mainly lookging to find the cause, and know the motor is fixed correctly. I have never torn down a motor and trouble shooted one like this, and i figure a spare one is a good one to learn from.

Thanks for all the input, I appreciate you guys making sure i dont blow the good motor, and any other sugestions you guys may have on possibly making this better than factory specs would also be greatly appreciated.