Hi,

I had my 85 at the mechanic for a new wheel cylinder. When he started up he car to drive it into the bay, it stalled out, I think, and he restarted it, revved it up to about 3,000 for a few seconds. As he drove it into the bay, I heard the engine making a loud knocking noise. I almost cancelled the brake work, but let it go ahead.

Started up the engine on the lift to pump the brakes. Same loud knock ! Mechanic said maybe it was making noise because it was on the lift !

Later on, lowered the car down, started up engine. Same loud knock. 2 mechanics and the owner listened to it. One said it sounded like rod knock, or spun bearing, the other said "that doesn't sound good". One said fan might be hitting something. It was loudest on the passenger side, near fuel pump.

As we were listening, the sound got quieter, and almost went away. Took about 3 or 4 minutes. On the way out, the owner told me that it might be a cracked flywheel or a cracked piston.

I drove it home, with the new wheel cylinder. Noise was gone. Started it up after I got home, and the oil light stayed on about a second or two after I started it ! Since then have started it about 6 times, and the oil light goes off right away.

Have driven it about 100 miles since it freaked out, and all is well. No knock.


My theory is that a chunk of carbon dropped off something, and was getting banged up slowly, until it got pulverized, hence the sound went away. ANother theory : fuel pump, but why would the sound go away ? Another theory : oil flow was blocked by sludge or a chunk of carbon to whatever was knocking, but the blockage cleared. I change the oil and filter every 4,000 miles or less, but even so, I've had loud lifter ticks on the past on this car, which go away by themselves, or after I add some Marvel Mystery oil to the crankcase. But this wasn't the same sound as a lifter tick, more of a low ugly rod knock sound.


Any ideas welcome.

RC

Hi,

I had my 85 at the mechanic for a new wheel cylinder. When he started up he car to drive it into the bay, it stalled out, I think, and he restarted it, revved it up to about 3,000 for a few seconds. As he drove it into the bay, I heard the engine making a loud knocking noise. I almost cancelled the brake work, but let it go ahead.

Started up the engine on the lift to pump the brakes. Same loud knock ! Mechanic said maybe it was making noise because it was on the lift !

Later on, lowered the car down, started up engine. Same loud knock. 2 mechanics and the owner listened to it. One said it sounded like rod knock, or spun bearing, the other said "that doesn't sound good". One said fan might be hitting something. It was loudest on the passenger side, near fuel pump.

As we were listening, the sound got quieter, and almost went away. Took about 3 or 4 minutes. On the way out, the owner told me that it might be a cracked flywheel or a cracked piston.

I drove it home, with the new wheel cylinder. Noise was gone. Started it up after I got home, and the oil light stayed on about a second or two after I started it ! Since then have started it about 6 times, and the oil light goes off right away.

Have driven it about 100 miles since it freaked out, and all is well. No knock.


My theory is that a chunk of carbon dropped off something, and was getting banged up slowly, until it got pulverized, hence the sound went away. ANother theory : fuel pump, but why would the sound go away ? Another theory : oil flow was blocked by sludge or a chunk of carbon to whatever was knocking, but the blockage cleared. I change the oil and filter every 4,000 miles or less, but even so, I've had loud lifter ticks on the past on this car, which go away by themselves, or after I add some Marvel Mystery oil to the crankcase. But this wasn't the same sound as a lifter tick, more of a low ugly rod knock sound.


Any ideas welcome.

RC

sounds like piston knock,,this maybe the piston wrist pin may have lacked lubrication...the distributor has a shaft that goes to the oil pump maybe it is worn...check/install oil pressure gauge to monitor the pressure..should be 40-60psi..

don't use fram filters,,,they break apart internally..

Had same thing happen to me with a 91 p/u years ago. I thought the engine was coming apart. It cleared itself up pretty quick once that piece of carbon burned off.

Go to your local GM dealer and get an aerosol can of GM Top Engine Cleaner, use according to directions.

If you don't have GM dealer, find a Dodge dealer and get Mopar Combustion Chamber Conditioner and use it according to directions.

JCAT, CD,

Thanks for the replies. Hoping it's just carbon. I did use GM Top End cleaner about 100K ago, to try to fix a knocking (ping) problem. Carboned up again, maybe.


RC

That's a once a year preventative maintenance issue for me any more...On all of my vehicles.

I had my 85 at the mechanic for a new wheel cylinder. When he started up he car to drive it into the bay, it stalled out, I think, and he restarted it, revved it up to about 3,000 for a few seconds.

Unless the engine is at full operating temperature, revving it cold can cause serious damage.

Later on, lowered the car down, started up engine. Same loud knock. 2 mechanics and the owner listened to it. One said it sounded like rod knock, or spun bearing, the other said "that doesn't sound good".

That's a prime reason not to rev a cold engine.

about 4 years ago i was on my way to work in my 83 caprice, i was stopped at an intersection waiting for a chance to go. when i start to go the damn car stalls and dies in the middle of the road, im sitting there cranking and cranking and it just will not start. so i hold the accelerator to the floor crank and it fires, but the pedal sticks to the floor, revving it to god knows how high... when i get it unstuck i got this horrible LOUD knocking/wrapping noise. it goes on for three days, i figured i collapsed a lifter. it turned out to be a stuck valve and went away on its own