Hello All,

I have a 1996 454 that has developed a knocking sound - block number #14015445. Youtube of the knocking here:


It is a low frequency knock or rattle, that is intermittent at idle and comes on strong at revs. The frequency is so low it does not seem to me to be bottom end.

I do not know a lot about the history but am led to believe it has aftermarket heads and a cam; the heads were rebuilt (skimmed / valve job) just prior to my purchasing the boat. The carb is an edelbrock 750.

The engine suddenly started knocking from the port side bank at around 3,000rpm after a long day on the water (literally 300m from the trailer); there were no obvious signs of any performance deterioration - the engine held revs, continued to put out power until I cut the revs. The engine hours show 550 ~ assume this was from last rebuild, or completely incorrect as can't be total since 1996. I have only put a few hours on the engine myself. The day before taking the boat out I had replaced oil / fuel filters, changed bravo gearcase oil, put new block plates and gaskets on the exhaust manifolds (after some signs of coolant leaking externally) - I have a closed coolant system.

Here is what I have done so far in terms of diagnostics:

Compression test (unfortunately with throttle plate closed)
1: 125 2: 135
3: 150 4: 145
5: 135 6: 150
7: 130 8: 150

Oil Pressure
45psi cold dropping to 25psi warm (at idle ~700rpm)
No visible water or metal in the oil

Stethescope
Difficult to pinpoint sound but seems to be front and port bank (passenger side).

Ancillaries
Disconnected all belts; no change to sound. Took fuel pump blanking plate off and confirmed pushrod is bottomed out (fuel pump is remote mounted on raw water pump).

Borescope
Checked each cylinder, some scoring (see picture) but no obvious signs of damage - valves look good and visually close.
No sign of any water/coolant in exhaust.

Valvetrain

• Nothing visibly loose, TDC and through the cycle no loose pushrods or rockers except side to side movement.
• I tried tightening exhaust valve on #1 with engine running (as closest to source of sound) and clacking dropped but engine bogs and dies (assume indicative of valve staying open). Other valves tightening did not effect the sound. This led me to assume a stuck lifter - I pulled lifters on #1 and they were both pumped.
• I inspected the camshaft - no visible signs of wiping - cams are all there.

At this point I had to leave the engine, and am currently sourcing gaskets so I can put it back together - my plan is to pull all lifters, take apart and clean and then reset the lash, and just pray it has gone away.

Any insight on this greatly received.

Thanks and Best
Will

well to start that is not a 1996 block, that is from 1990 or earlier so if the boat is a '96 then that is a different engine that someone put in. as to the noise that does sound lifter ish but hard to tell in the video. I have had lifters that would seen pumped up but would not hold under pressure and would rattle so not out of the question. also sounds like an exhaust leak but again hard to tell but does not really sound bottom end. I did have that same sound on my dad's boat and when I pulled the rockers half of them were grooved out from wear. seems chevy didnt harden the rockers properly. put new ones on and all quite now.

cam exhaust lobes on 2 and 4 look suspect,,lifters don't look to be out of the bores the same as the other lifters

Thanks - yes of course you are right, I obviously misread that on the casting number dates. Any idea about the heads?

Rockers look OK - and lifters look fresh, which has me concerned that maybe they changed them when refreshing the heads and didn't change the cam at the same time. I will be back to the boat next week with fresh gaskets and will investigate the cam more closely (ref comment about #2/#4 lifters - thanks). I will pull all the lifters and clean them out for good order, and put her back together and see what happens.

One other thought was perhaps something in the timing chain area, but I guess a loose chain wouldnt slap consistently with one cylinder would it?

Check the flywheel area too. Loose bolts can knock pretty loud. Does sound like bottom end though by frequency.

Hi All,

Just an update on this - after the leaving the boat alone for a week whilst I sourced gaskets, oil had drained back to sump and slivers of copper clearly visible in heads and v of engine.

Likely thrust bearing or a very worn big end I am told. Looks like the engine is coming out.

This happened on the first trip out after changing the oil filter ~ just coincidence or something I did wrong here?

Thanks
Will

Probably coincidence

Engine looks awfully dry

Can you expand on that? The dipstick was showing oil, and oil pressure Ok.

How can you tell it is dry, and what might that imply?

Thanks
Will

Is there oil in the lifter pockets or puddling on the rocker arms above the valve stem, maybe its just the picture