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Mercruiser 7.4 Horizon a tick to a knock

H

Harborite88

New member
1998 7.4 Horizon 380hp in a Sea Ray started to tick then developed into a bit of a knock, the factory oil pressure gauge went from 60 at WOT to less than 40. Here is a video to add some sound to the issue.

 
Bt Doctur said:
loose rocker arm, bent pushrod, pulled rocker stud, stuck/bent valve
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Ok, so I removed the intake manifold, rocker covers, and the lifter guide hold-down plate. All of the lifters move freely, and don’t appear to be scored. The rockers don’t feel too loose in there TDC position. The cam lobes that I can see aren’t scored. The pushrods don’t appear to be bent. So next step remove the rockers and pushrods, roll the pushrods across the table and see if one has a slight bend?
 
started to tick then developed into a bit of a knock, the factory oil pressure gauge went from 60 at WOT to less than 40.

So next step remove the
Click to expand...

Ayuh,..... Next step is to pull the motor, 'n strip it down,....

Sounds more like yer gonna be rebuildin' the bottom end,....
 
bondo said:
Ayuh,..... Next step is to pull the motor, 'n strip it down,....

Sounds more like yer gonna be rebuildin' the bottom end,....
Click to expand...

With all of the videos I’ve been watching it is starting to sound more like maybe a rod bearing has spun than a valvetrain issue. I was just hoping it wasn’t something like that.
 
harringtondav said:
Engines aren't my strong suit, so I'm asking more than suggesting. Are the lifters hyd. to take up slack? If so, could one be bad?
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Yeah, they are hyd. roller lifters. A collapsed one could make a noise like this. But, I think usually you would have a really loose rocker on one of the valves that would indicate something like this was happening. Unless I’m missing something, I’m not seeing anything wrong with the valvetrain yet, which sucks. I will keep investigating after I get off shift though.
 
Harborite88 said:
Yeah, they are hyd. roller lifters. A collapsed one could make a noise like this. But, I think usually you would have a really loose rocker on one of the valves that would indicate something like this was happening. Unless I’m missing something, I’m not seeing anything wrong with the valvetrain yet, which sucks. I will keep investigating after I get off shift though.
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Not trying to play out of my league here, but the noise didn't sound like a deep crank or connecting rod knock. But I wasn't there. Think about what causes a drop in oil pressure. Unfortunately that includes a loose con rod. Any where else an oil gallery feed might have little too much clearance?
 
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