I have a 396 +.060 thats got about 40,000 easy miles in my truck. Lately when I start it up it sounds like it doen't have any oil in it. heavey pounding from the lower end and yes it has 80 psi oil pressure cold and about 15 at idle when warm. where should I start?
Start with a mechanical oil pressure gauge on the front of the oil rail. Find out how much oil pressure you are really getting.
does the noise go away quickly after oil pressure comes up, or doe it keep knocking? I hate to say it but the 396 seems to lose bearings....hope that's not the problem.
I dont have an answer but I bet this engine made a hell of a rattle before the broken valve stem finally wore into water in the exhaust chamber!
the noise does go away at idle, but return when you rev the engine quickly. I drove the truck a couple days ago and drove it pretty hard for the last couple miles and did not seem to make a differance. it is almost like an octane knock but louder
Pull the oil filter, cut it open and examine the media looking for metal flakes. You may find the answer if you see bearing material. Are you positive it's not lifter noise rather than bottom end?
Like was said , piston slap in BBC pretty common , The 454 in my dually has been rattling for about 60K miles, has about 145K on it , drive it!!! dave
I had a 396 that had a terrible bearing knock and had 60 PSI of oil pressure, pulled it apart and found a spun main bearing. So expect something like that. Mine had lots more than 40K on it, but was well cared for. Bob
Sure sound like a possible bearing issue... like already said not that uncommon in early big blocks. Why take the chance of expensive damage? Check the filter for bearing and /or pull the pan and check.
We had a 454 in a truck that we used to haul our car trailer with. It wasen`t driven much, and developed a loud knock. This motor had very few miles on it, but we wern`t sure if if it had knocked a bearing out or what the problem was. A friend of ours, an excellent professional mechanic, said it was carbon buildup and to pour water through the carburetor and it would solve the problem. He was right, and it worked just like he said. This may not be your problem, but that cured the knock in our truck.
My two cents - have someone familiar with engine noise determine whether it is top end noise or lower end noise. They can use tricks with stethoscopes or rods to help pinpoint where it's located, then give you a GOOD guess as to where YOUR noise is coming from, and a PROBABLE reason. At that point you drive it 'til it destroys itself or you fix it, based on your budget and needs in this vehicle. ie: only transportation and piston slap? Drive it while you find a spare engine. Secondary vehicle/severe rod noise? Park it on the slab and start pulling the engine.
Unfortunately I'm well-versed in bad engine noises. It pays to have another opinion. Bearing noises can be narrowed down to a cylinder by taking the plug wire off each cylinder (removes the load on that bearing) until you find the bad one(s). Usually it is only 1 to start and a good ear can tell which bank it it. Bob
If it's a 2 bolt 325 hp 396, they were prone to a spun bearing at the rear of the crank. I don't remember exactly which one BUT they had a problem with the oiling in that area. You're better off pulling it down than to risk it coming apart on the road..
I have had fuel pump springs get weak and the sound of the fuel pump rod bouncing can lead a person yo thinking it was bearings.
Does the engine noise seem to be the same rpm as the crank or half the engine rpm as in valve train noise?
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