Disassembled Mercruiser 4.3 Knock?

[incrediblened]

I've got my Mercruiser 4.3 engine all torn down. Head & block decks are free of gasket residue and ready for head installation. I was doing a final cleaning and using the starter to turn the engine over. And I noticed something I didn't notice before. A KNOCK when the 1 cylinder hits TDC.

I've been working my butt off to get this engine ready to re-assemble - and now I'm afraid that the engine may be bad. Lemme know your thoughts.

 

[incrediblened]

Re: Disassembled Mercruiser 4.3 Knock?

Well, I decided that I'm gonna install the heads anyway and see what happens. (I've got a spare engine if this one desides to go).

 

[93maxum4.3lx]

Re: Disassembled Mercruiser 4.3 Knock?

I would do a bit of detective work to see what's making the noise.

Possibilities:

* rod bearing on #1 is installed incorrectly / has play. Inspect #1 rod bearing, plastigauge all rod bearings to verify they are within tolerance.

* piston pin on #1 is loose for some reason, inspect

* piston may just be rocking in its bore. Depending on the condition of the motor (is this a new rebuild? a re-ringed old motor? just plain worn out?) you could possibly get an audible tick/click type sound as the piston rocked slightly in the bore as it crosses TDC. Same as before - got to inspect it! Do the other pistons rock an equal amount? Is there any reason the skirt on the #1 piston might be knocked in and allowing the piston to rock more than it should? If the rings weren't installed the piston would fit even looser in the bore, any chance that piston doesn't have it's rings installed? You can measure the skirt diameter to see if it's been knocked in at all...

 

[Yepblaze]

Re: Disassembled Mercruiser 4.3 Knock?

Does this have a mechanical fuel pump that could be making sounds?

 

[incrediblened]

Re: Disassembled Mercruiser 4.3 Knock?

Well, I don't have the engine out, so I can't check the rod bearings or the piston thoroughly without pulling the engine.

Mechanical fuel pump - YES!

 

[Polar_Bus]

Re: Disassembled Mercruiser 4.3 Knock?

Well, you will know the second you fire up your engine if you have a faulty internal component, if you are hearing a "knock" just by turning the engine over by hand, you will DEFINATELY hear a louder knock, when she fires....

 

[Robj]

Re: Disassembled Mercruiser 4.3 Knock?

Why would you install the head when you know there is a problem? Are you hoping it will magically heal itself?

Doesn't make sense to me either. Like Don S. says, why is there time to do it a second time but no time to do it right the first time? or something like that. Do it right and then forget about it.

Have a great day

Rob.