Engine Knocking!! Help!!!

[gmcsierra93]

I own a 1993 GMC Sierra 1500 2WD 5.7 350 V-8 with 177,000 miles. Brought truck to repair shop to have rear main seal fixed and the intake manifold gaskets replaced. When I got the truck back I had a real bad knocking sound coming from my engine.

Next I had the oil pump replaced along with a new oil pan gasket and had the main bearings replaced hoping to fix the knocking. STILL NO LUCK!!! The truck has low oil pressure now for some reason and runs a little hotter than usual. Somebody please help. I'm running out of patience and money!!

[Galaxi-99]

Hmmm, did you have a problem with this engine before you took it to the shop?
Does it knock at the bottom of the engine or does it knock while your driving it up hill under a load.
If it is your rods knocking you will need to pull the engine apart and put new bearings on the cranck shaft,,,after you take it in to have it checked out if it is any good.
If it knockes up hill under a load then i would look to see if the anti-knock sencor is un plugged ,,,,check the timing,,,,and put a higher grade fuel in the truck.

[gmcsierra93]

I did not have any problems before I took it to get repaired. The knocking seems to be coming from the bottom of the engine. It knocks at all times except early in the morning when the oil pressure is around 30 psi. but after i drive it, the knocking starts. I brought it there to have a oil leak fixed, I had good oil pressure before I took it there. Now everything is bad. Bad oil pressure and bad knocking.

The mechanic said it sounded like the main bearings and not the rod bearings by the type of knocking it is. Its a deep knock, not really a pinging noise.

[Redneck_Cadillac]

Originally Posted by gmcsierra93

I did not have any problems before I took it to get repaired. The knocking seems to be coming from the bottom of the engine. It knocks at all times except early in the morning when the oil pressure is around 30 psi. but after i drive it, the knocking starts. I brought it there to have a oil leak fixed, I had good oil pressure before I took it there. Now everything is bad. Bad oil pressure and bad knocking.

The mechanic said it sounded like the main bearings and not the rod bearings by the type of knocking it is. Its a deep knock, not really a pinging noise.

if you only have 30psi oil pressure when cold, then you have excess bearing clearence in the bottom end bearings. you should have 50-70+ when cold. (avg 70F degree) 30lbs is what i'd expect at idle, when at operating temperature.

once the engine knocks, (bearing knock on the crank) generally, the crank is already damaged and needs to be repaired or replaced. dropping new bearings on a damaged crank is a waste of a mechanic's time and your money.....

you said he replaced the main bearings.....but not the rod bearings??? (initial repair) did he at least check the rod bearings while the pan was down???

rod bearings will knock 10 times more likely, before a main bearing. main bearings *generally* won't knock, rather cause a lack of oil pressure, or spin in the block, if due to oil starvation and make some other lovely noises..... they will get damaged quickly though, if debris is being passed around due to a metalic failure elsewhere in the motor....

personally.....if it's the same mechanic that did ALL this work...somethings not right. if it didn't knock when it came in, why now?

*granted*, you've got high mileage on the motor, but i'd never recommend to a customer to only do some bearings (and certainly without plasti-guaging them) and not others, or atleast check others, with that kind of mileage. with all things considered: i'd replace the motor at this point, or rebuild the one you have. any more money in that motor with that mileage is not a good idea...........

i can only assume as to why you have the problem now, based on what you've said. i hope things work out for you..........

[Pewter'01SS]

They might have f**ked up while putting your oil pick-up tube back on the oil pump. Too high or too low will cause problems. They can't return your truck to you knocking when it wasn't before. Threaten to take them to small claims court or something, that's just not right.