Engine stopped running/loud knock when cranking.

[Patchwork1]

So we dropped the boat in the water, and it was running fine for about 30 min. Then the engine bogged down and shut off. We were able to restart it a few times, but it was barely able to stay lit, and ran poorly. Once we got it back on dry land we did the usual stuff.

Checked the spark plugs
Checked the coil/distributor
Checked the carb and fuel flow
Checked the shift interupter switch

We then noticed a loud clang when we would crank the engine. It doesn't happen when the engine lights and runs poorly for a few seconds, but when the engine is just turning over this sound is present. The block and head was just professionally rebuilt by a local shop that works on these engines specifically. Any thoughts?

OMC cobra
4 cylinder 3.0L
The boat is an 88' Chris Craft

Thanks!

 

[Don S]

Re: Engine stopped running/loud knock when cranking.

Did you crank the engine with the spark plugs out and see if there was any water in the cylinders?

Where is the knock coming from, you should be able to hear if it's from the starter area or the engine itself. Might try a mechanics stethoscope.

A compression test might reveal the problem.

 

[Patchwork1]

Re: Engine stopped running/loud knock when cranking.

No water in the cylinders. The knock sounds like it is coming from the back of the head. Everything looks good on top of the head. All the rockers are operating properly. Valves seem to be opening and closing. It might be time for professional help. We were just hoping we could get her back in the water for the weekend.

 

[Howard Sterndrive]

Re: Engine stopped running/loud knock when cranking.

pull the outdrive off and try it. / check drive oil

 

[Patchwork1]

Re: Engine stopped running/loud knock when cranking.

So upon closer examination I noticed one of the rockers is the source of the knock. it seems that as the valve closes, something happens internally and the rocker shutters with the loud clang. I can't tell if something is happening down on the cam or somewhere else. The valve looks to be closing properly, so I don't think that is it.

 

[Bondo]

Re: Engine stopped running/loud knock when cranking.

So upon closer examination I noticed one of the rockers is the source of the knock. it seems that as the valve closes, something happens internally and the rocker shutters with the loud clang. I can't tell if something is happening down on the cam or somewhere else. The valve looks to be closing properly, so I don't think that is it.

Ayuh,.... So, pull the head, 'n have a look...