4.3 Mercruiser

[countryboy996]

I have been having a ticking noise coming from the rear of the engine. Yesterday I was out cruising about 3800-4100 RPMs and all of a sudden it cut off and came off plane. I tried to restart it afterwards as it turns over, it clunks on every revolution of the engine. It wouldn't start up after this. So I pulled the distributor it looked fine. I pulled the valve cover on one side, some rockers I could push down on the lifter some I couldn't. The rear most rocker, I couldn't push down however there was about a 1/4 inch of play between the rocker and push rod. Several of the others were loose also but they were on the ones that I could push down on the lifter. Any ideas>?

 

[Silvertip]

It takes considerable pressure to push down ANY of the rockers on valves that are not pushed open by the camshaft. If there is any gap between push rods and rockers there is a serious valve train issue that can range from bent push rods, misadjusted rockers and rocker studs that are pulling out of the cylinder head. With 1/4 inch gap between rocker and push rod it is odd the push rod didn't get dislodged and forced right through the valve cover. These serious valve train issues need to be investigated and corrected.

 

[countryboy996]

do you think this would cause the knocking issue?

 

[Rick Stephens]

I was earlier going to post that it was my opinion the motor needs be pulled and torn down. All the stuff you mention indicate significant internal wear or damage, at least to the valve train. Certainly that can knock. It can even be rapping stuck valves with pistons.

Rick

 

[Bt Doctur]

pull the drive to verify its not the U joints
remove the spark plugs and try to spin the motor , watch the rockers for movement, no movement could be a broken timing chain or cam break that caused the pistons to impact the valves.
Next ,remove the heads to inspect the internals
post pics of what you find