rjoyal

Helping a friend with his 81.
It's been parked for a few years, so first thing was getting it running...

And now it's knocking.
It's an intermittent knock - almost sounds like a lug nut in the oil pan being kicked around.

Of note: part of the reason the car was parked was because the balancer separated and was rubbing on the timing cover.

It doesn't seem to get worse or better if the engine warms up.
It doesn't seem to get worse or better in gear or park (the car isn't insured so a road test is not possible.)
We tried pulling one plug wire at a time and it got WORSE as we dropped a cylinder - I thought if it was a connecting rod bearing it would go away when we did that.

I tried getting a video but it didn't really cooperate - it comes and goes: https://www.dropbox.com/s/irt24zg3n9...2021.15.33.mp4 - it's right at the beginning of this video, right when the car starts.

The car has had the cam replaced in the past. That's all I know about the history of the engine. The jury is out. We're probably going to drop the pan and check clearances or just pull it and do a teardown. It's an 81, and Greg's looking to cruise, not race, so a 260HP GM crate motor just might be adequate for him.

I apologize for the dirty engine compartment. Not my car.

Considering the hell we had to go through to get it started *I'll post about that after* and how long it's been sitting, it does seem to run fine. My friend's Nova was doing a similar knock, and when we pulled the motor, it was basically the mains being ALL worn. Is that what he's looking at here?

I'm open to suggestions on what to check before we just yank it.

rjoyal

And now, how to have everything go wrong trying to start an 81 Corvette that has sat for about 8 years because the balancer is broken (among other things...)

Remove half the front end to install the new balancer.
When going to install the balancer, have the balancer installer tool snap.
Then, discover the threads in the crank are buggered so you need to drill and heli-coil it after trying things like a longer bolt...
Oh, right, the battery is dead. And the battery terminals are gross.
Time to crank 'er over. Oh wait, does this thing have any gas in it?
Hell yes, it does. The float has sank/stuck so it's a gas geyser!
Flooded the hell out of it.
Try mounting a friend's Holley 600 on an adapter.
Hey look, the float on the Holley is stuck too!
Fix the Holley - still won't start - try and set timing, timing light implies coil failure or weak spark and/or unhappy computer because factory QJet is on bench.
Swap in "normal" distributor.
Now we're backfiring out through the adapter/intake interface because the adapter won't seal to the intake properly.
Take Holley off, borrow QJet of unknown origin from another friend.
Battery's dead again. Other battery has sideposts so we have to rig up something to 'make it fit.'
Anyone know what the hell the timing is?
I think we're now out of gas.

Eventually, we got it running to discover the engine knock. It's a good thing it's a Corvette because otherwise:

I did convince Greg to give me the distributor to use in my dirt track car - no advance mechanism - apparently a lot of guys just weld it up and lock it at 34 degrees of timing so they don't have to worry about stuff breaking.

It also answers the question of "How do you get rid of the computer on an 81 Corvette? Swap in a non-computer controlled carb and distributor like it was an 80."

SIXFOOTER

Lol

garygnu

mite be a sticky lifter .remove the valve covers and spark plugs .rotate the crank with a big ratchet.look for any loose rocker arms ,wiggle the push rods to check for any slack.

oldschoolvette

make a video that shows me a little more than that...

I here the noise but need to here more than that to wrap my mind around it

I rule the lug not in oil pan out..

ur welcome

TimAT

Fuel pumps can make a knock too.

Tim 1973

Remove the fan belts to rule out AC pump, power steering pump, water pump, and anything being driven by the belt. Inspect the belt to make use it does not have a bad spot on it.

hugie82

Check the flywheel bolts if its an automatic and in rare cases a crack in the flywheel can make a knocking noise too.
Since you said the cam was done I would think they spent the extra $30 and installed a new timing chain, if not, that can knock against the cover if it gets stretched enough

The good news is the knock doesn't change in gear when hot. Usually it will not knock cold and knock like crazy warned up at low rpm....

rjoyal

ok, thanks. I'll see if I can get a better recording of the sound, and then I think the plan is to proceed with removing the accessory drive, checking the timing belt and fuel pump, and pulling the valve covers to check the valvetrain... and then yanking it if everything looks good, but maybe pulling the pan first to plastigage a couple of bearings. And also the flexplate bolts.


we keep trying to talk him into a 500 horse crate motor, but he just laughs...

Easy Mike

Talk him in to taking the car to a shop and letting the pros have a look at it.