Yesterday the boat was running great. Topping 80 no problem. Then I stop and the exhaust sounds funny. Port side exhaust felt like 2 cylds not firing, starboard side seemed normal. Also loud clacking from top of engine toward the back, couldn't tell which side. Revving engine there was no bottom end knock. Now I have rocker covers off and all looks good. Compression is over 150 on all cylds. Plugs look good. Where do I go next? Could an ignition issue cause a ticking/clacking sound? Thanks in advance. This is my first issue with this engine. Top end service was done at 400 hours. Engine has 500 hours but mostly idle speeds.

A "clacking" sound as I'd interpret it means mechanical issues, metal not being where its supposed to be. I'd lay out some towels around to catch the little bit of splatter and start it with the valve cover off one at a time and isolate the sound, its almost gotta be valve train. I run the valve on my race engines with the valve covers off, its not a big deal if you don't rev or run it long. Also maybe try using a cardboard tube like gift wrapping paper comes on to listen around the top end while running to see if you can isolate where the sound is coming from. Does that engine have a distributor? If so pull it and check the gear and teeth.

Duplicate post

The problem here is that I'm not just tracking down a noise but I also seem to have a couple dead cylinders. Each coil sparks two cylds. Has anyone heard of a bad coil pack making a clicking/clacking/snapping sound? The sound did seem to be coming from the area of the coil packs.

I had a problem like this with one of my 525s on previous boat and it turned out to be the sensor on the oil drive (takes the place of the distributor). When I would load the engine it would sound like someone was hitting the exhaust with a metal hammer, Nothing wrong at idle or just cruising. I also had a crank position sensor go bad and it caused a pinging like bad gas but easy to change. Shoot me a pm if you want to discuss further, maybe I can brainstorm with you.

Thanks. I appreciate the help. Let's see what others have to say but now I'm leaning towards putting it back together to run on the hose and see what happens.

It does have silent choice which I use only at idle sometimes.

I put it back together and ran it on the hose. Exhaust now sounded normal and engine seemed to be running good. Tapping was at rear port side. Pulled valve cover back off and one rocker arm has about 1/4 inch up and down movement. Rocker looked ok so now the intake will come off and hopefully it's just a collapsed lifter. I guess it could be a wasted cam and lifter but valve lift looked about normal and there is no visible metal in engine. ��

I also found 4 stored fault codes that I don't know what to make of:
94. Pitot Pressure (boat speed sensor) Low
75. Fuel Level 1 Circuit High
118. Steering Position Circuit High
191. Fuel Level 2 Circuit High