Jams

Can anyone help me identify this noise?

http://www.youtube.com/watch?v=DlLK2YYSi3s

This is a 1989 350 TBI in a Camaro (Vin E) using a truck engine (Vin K) and the original 305 heads. I found out the engine was severely overheated with both heads cracked before I acquired and rebuilt the block. The block had all new bearings, lifters and other replacement parts installed, except the oil pump. That was an error on my part.

I don't know if it's a rod, main or something else, and because of how it knocks, nobody else seems to know exactly what it is since it mostly does it when letting up on the gas.

It does this after it's warm and the oil pressure will drop way down after warm and clear to 0 at idle.

It's been doing this for 8 years, which makes a lot of people scratch their heads.

I'm afraid it's going to get worse since I've been driving the car more often after scrapping my Buick.

Thanks for helping out a newbie.

72c10gunn

Maybe piston slap??? But that wouldnt explain the low oil pressure, have you checked all the accesories ie alternator, ac compressor, water pump ect. to make sure that the pulleys are tight and they dont have any play in them.

Jams

Everything seems to be in order and I just replaced the power steering pump, so I know everything is tight. I was thinking about dropping the pan and checking each bearing and also change the oil pump.

It's just strange that it's been doing this for 8 years. When this happens, you can touch the throttle body, intake or valve covers and really feel how hard it hits. I just wish I could figure out what it is so I can try to somehow get it taken care of.

The low oil pressure is what makes you think it's a bad bearing. I was told the oil pump could be doing it, but I doubt it could knock that hard throughout the engine. The oil pressure is over 30 when cold, but then drops way down after it's warm, which is when you can really hear the knock on deceleration.

It's going to put me in the nuthouse if I can't figure it out soon! If I had the money, I would simply replace the engine, but I'm too poor for that. lol

2wd-K5

my sound card is busted right now, so i cant hear it, but under deceleration, seems like piston slap, take a compression test, usualy spun bearings make more noise under load, and were caused by heavy load on the engine (burnouts are famous for spinning bearings), the low oil pressure is just from the miles on it, chevys lose oil pressure at a hot idle when they are worn. try some strait 30 wieght oil and see if it helps with oil pressure, conventional 10w-30 thins out when it is hot, i use it in worn out chevys to get some extra life out of them

Jams

Before dropping it in the car, it had new bearings, rings and all the other basic overhaul stuff done to it and has done this ever since first start, which is weird. The oil pump was not replaced though.

The cam bearings were even replaced. I'm kicking myself on the oil pump.

No other knocking for 8 years, but it is not worse under load. Actually quiets up a little after putting it in gear.

This is definitely a mystery, but I don't think it should go to 0 at idle with new bearings. The original 305 had a good oil pressure and it smoked.

If you could just feel how hard it knocks when touching the engine. It's like someone is beating the hell out of it with a hammer from inside.

2wd-K5

yea the old oil pump could be a reason for low pressure, did u plastiguage the bearings? also did you hone the cylinders and put the original pistons back in? pretty easy to over hone the cylinders and make a piston walk around (it doing this since first start, makes the piston slap idea hold) but we will never know unless the engine is pulled out and taken apart

Jams

Nothing was done to it. Just a backyard mechanic job.