Help! Loud tapping/knocking noise after warm up

[C3L81GUY]

Hello everyone! I have a 1981 with the original L81 (190 HP) in it with 87,000 original miles, side pipes but no headers. Other than the side pipes, everything else is original, decent shape. Today I started it up and let it idle in the driveway, hood open. After about 5 minutes I heard a loud tapping or knocking sound as if metal against metal around the motor. No smoke from exhaust, oil level good and clean. It sounded like it was outside the engine, not inside it. I shut if off and let it cool. I later started it again and there was no sound but I didn't let it run long this time. I called my mechanic and he just said to "bring it in, Ok to drive it". I'm not a mechanic. My questions are: Should I drive it the 6 miles to a mechanic? And, in your experience, is this likely rod bearings or something major requiring expensive work or a new motor? Or maybe just a timing belt tension deal? In a worse case scenario, where's the cheapest place to get a decent rebuilt or new 350 crate motor and at what cost? And finally is a crate motor a better route to go than having a mechanic just rebuild it? I'd have to have a mechanic put a crate motor in anyway, can't do the job myself. I feel inclined to just upgrade to higher HP (close to 300 or better) in a crate if the cost is about the same as a rebuild. I see a few on the internet for 1995.00 or 2995.00 for the same engine turn key, although I believe the distributor and carb are good for a swap. Any guesses? Any comments or suggestions would be greatly appreciated. Regards, Bill

 

[TimAT]

Was it missing? Or running as usual? Any popping from the intake or exhaust? Those would be signs of the cam going away. But if that WAS the case, it would do it all the time- even cold. Take a long screwdriver or metal rod and set it on various places stick it up to your ear and see if you can figure out exactly where the noise is comng from. Be careful of moving parts !! A timing chain won't make any noise, the engine will just quit and won't restart. Could be the air conditioning compressor front bearing too, but they usually just lock and smoke the belt.

I'd just about bet that your fuel pump is the problem since it's running fine just making some noise.

 

[C3L81GUY]

Was it missing? Or running as usual? Any popping from the intake or exhaust? Those would be signs of the cam going away. But if that WAS the case, it would do it all the time- even cold. Take a long screwdriver or metal rod and set it on various places stick it up to your ear and see if you can figure out exactly where the noise is comng from. Be careful of moving parts !! A timing chain won't make any noise, the engine will just quit and won't restart. Could be the air conditioning compressor front bearing too, but they usually just lock and smoke the belt.

I'd just about bet that your fuel pump is the problem since it's running fine just making some noise.

Hi Tim,
No, it wasn't missing, just running as usual. No popping observed, but I have heard the side pipes popping before on the street at idle. The guy
I bought this C3 from had them installed before I purchased it. This is a different noise; more engine located. Didn't turn on the AC, but it worked good last week. Don't know if a fuel pump can make that loud a noise around the motor...I'm hoping it's just an exhaust manifold or something less than an engine fix. But would a manifold make the same noise cold starting, or only after warm up? I won't know what the issue is until mechanics look at it. I'm not a rich guy; I only look like one in the car

. I just like the C3 body style (could never afford C2, my favorite). This is my third C3 (money pit) LOL... but each one has been a progressive step up...Thanks, Bill

 

[6880 Mike]

No need to talk replacement engine until you determine what's going on. Take her to your mechanic.

 

[Chrisr]

How's your oil pressure?? Way back in the day when I had my C3 (1980 L81), I had a loud tapping noise. All seemed fine other than the noise, took it to the dealer (still under warranty) and turned out to be the oil pump went south.

 

[C3L81GUY]

How's your oil pressure?? Way back in the day when I had my C3 (1980 L81), I had a loud tapping noise. All seemed fine other than the noise, took it to the dealer (still under warranty) and turned out to be the oil pump went south.

Hi Chris,
It was 40 PSI on the gauge. (Did you mean an L82 in your 1980? In '80 I think there was only the L48 and L82 available. L81 was specific to 1981). Anyway, I'm taking it to a mechanic within the next few days.

 

[Chrisr]

My bad, it was an L48. I guess I still have some cold medicine in my system!!?? :L

Anyway, with mine, the pressure was good, just a quart low on oil. No biggie, I thought, until I took it to the dealer and found out about the oil pump. Hopefully yours isn't that serious.

 

[73shark]

Possibly a stuck lifter? Is it still doing it after it warms up?

 

[C3L81GUY]

Loud tapping/knocking noise after warm up identified

Many thanks to everyone who has responded to this thread. You guys are great!

The noise turned out to be a bad fan clutch. While he's at it, the mechanic found the water pump is starting to go south so he'll replace that also. Total cost of repair job? $300.00 parts and labor included. Does this price seem fair?
Cheers, Bill

 

[73shark]

Sounds a little stiff to me but then I do that kind of stuff myself so don't really have a good frame of reference.

 

[Crimson Thunder]

$300.00 is a fair price if he installs a genuine GM water pump.If he's just installing a rebuilt 19.95 repop from the local auto parts store i would worry.If you are an inexperinced mechanic this would be a great project to do yourself.