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Mercruiser 3.0 Thumping in exhaust

vroomZOOM

Regular Contributor
Hello

My 3.0 is making funny noises, most noticeably a clacking from the camshaft area it seems and a thumping in the exhaust. Have a look at the video. It ran like crap above 3800 rpm on the first time out this year, then it started running like crap at idle. I swapped out the plugs and it got better but now it picked up this thumping noise. I am thinking that the clacking might be the valves, but I am more concerned about the thumping. Is it ok or something major going on in the engine? Any suggestions to get this fixed?

Thanks
 
should I test cold or warm? Also of the piston broke it would have been much louder, no? and how would it run at all? Also there would probably be a boat load (worst pun ever) of blow by?

Thanks
 
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ok, here are the results of the compression test:

#1 170
#2 just over 160
#3 170
#4 same as #2

so it doesn't seem like a bad piston. I did the compression test at WOT and a cold engine. Any ideas now as to what i should be looking at? I thought #3 was the problem cylinder as that was where the tapping noise seemed to be coming from, but on the contrary it is the best of all. what the heck do I do now? At least I don't think I have to replace the engine! :) Funny that this issue popped up all of a sudden, and right after winter storage. I will also post a picture of the spark plugs right now, they seem WAY too sooty for new plugs that ran for a couple of minutes at idle speed.
 
The engine is now running properly, or at least like it did before. The clacking is still there, the thumping is gone. I think the cause of the thumping was the fact that my ears fell off the outdrive and it made big bubbles in the manifold, and when they came out in the hollow exhaust pipe they made the noise. As for the clacking, maybe a valve adjustment would help? How would I adjust the valves? Or maybe a collapsed lifter? I am really thinking this one might be probable.
 
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Well today it ran fine on the ears so I decided to go out for a rip. Got it in the water and it wouldn't start worth a can of beans! Smelled like gas but eventually I got it started and it ran like it usually did when warming up (in bursts). When it warmed up it ran real smooth and then a few seconds later it seems like a couple of cylinders dropped out, so I gave it some throttle to keep it going. I revved it up to like 2000 and it then stalled again, almost like someone hitting the shift interrupter. It then picked back up again. At that point I thought it might be running out of gas so I took it back out and went to the gas station to fill it up. came back, put it in the water and it still kept cutting in and out. F***ING engine! I'm trying to sell the boat and some guys wanted to come over for a test drive just when it broke down, lucky I hadn't called them. At the end of last year I put a new coil, cap and rotor in and it's still making a big loud blue spark. drained the contents of the fuel filter and no water in it at all, fuel is nice and clean. I doubt the carb would be acting up like that. Disconnected the shift interrupt switch, maybe that is the trouble? No, that did not help. It has new plugs in it gapped at 0.035. Last year it ran great, I took it out every weekend and it never gave me trouble other than the one time the coil blew (it was so rusted I was surprised it even worked). Now I start it up and it runs like a hunk of junk. What do I do? I need to get this thing fixed fast so I can sell it and not deal with it anymore! Only things I have not replaced is the carb and fuel pump! I don't have a boat load of money so I don't want to throw money at it randomly. Help me out please! There is something to be said for efi lol.
 
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