Knocking at Start up

[CanadianGriff]

I have a 1993 4.3 Griffith in Canada. Yes left-hand drive. At the end of last summer I noticed a rattle noise (knock) at start up. It went away once the oil pressure got up to pressure. I haven’t had a lot of seat time since this noise started, so I can’t say if it continues for long after it’s warmed up. Ot did sound like it was gone altogether.
I have been told it is a $5000.00 (3200.00 pounds) fix. New bearings and crank work. Also said I need not do it right away.

Any thoughts?

[roseytvr]

Worth checking its not a blowing exhaust manifold thats closing up when warm - this can sound more tappety than knocking though

[carsy]

Doubt it will be the crank. You would certainly know about that if that was knocking.

Check exhaust manifold gaskets as already stated. Could be worn damaged rocker/s. or cam followers. Difficult to say really without hearing it.

[BeastMaster]

Worth also checking engine mounts, if worn motor can move around a lot before smoothing out when up to temperature and knock against exhaust or chassis - Andy

[gizzer]

SOUNDS LIKE BIG ENDS!!!!

[spend]

Remove the plenum top & check the trumpets are still glued into the base.

Pop off the rocker covers & check the pads on the rocker arms are still there.

Use a stick to try & see where the noise is coming from, and a long pipe (like the screen washer or vacuum tube) to listen to the manifolds at the head & by the collector. It is sometimes easier to take the fan belt off to remove alt & water pump noise, fine to run briefly from cold without the belt.

Wooden wedges to brace the exhaust pipe & the like to check mounts & exhaust knocks are quick & easy as well..

If all else fails you can drop the sump to look at the mains, but it may be as simple as low oil pressure at start up due to the oil pickup pipe coming loose and/or the pickup blocked with crap (silicone // cork gasket bits..). Checking the reading on the oil pressure gauge when the problem occurs might shed a bit more light?

[Pupp]

The diagnosis of crank bearings is not entirely compatible with the suggestion that it need not be done right away. Can't see a competent mechanic advising that an engine with crank issues continue to be used.

If the thing is only run infrequently and the noise is after extended periods of non-use, it might be the lifters beeding down and re-pumping. That makes a bit of a racket for a second or two but is not really a 'knock', more a 'thrash'...

[EGB]

Oil pump wear, leading to low pressure at start up.