[69-er]

I know this is probably next to impossible to diagnose here, but what the hell...

During the cold months, after several seconds of running after start up, my 83 L69 knocks. Sounds deep within, like maybe a rod knock. It goes away after less than a minute of run time. I never hear it again till maybe the next morning. It doesn't always do it. I can envision it being oil related. If the oil is cold, it takes a while to get to the bearings, etc...

But get this, a couple of years ago, I disassembled the engine strictly for a gasket change-out, (big time leaks). I was having the knocking problem then too. I didn't find one thing wrong with the engine. Bearings were in good shape, normal wear on the cam, and I could still see remnants of the cylinder wall cross hatch pattern. Not bad for a 130,000 mile engine. Not wanting to break the ring seal, I left the pistons installed, and decided to change the main and
rod bearings, timing chain and sprockets, and gaskets. The noise is still there.

Maybe it's not engine related?

I never have a bit of trouble with the engine otherwise.

Go figure!! Who wants to take a shot?

Larry

[Dave Birdwell]

If it does it only when cold, it may be a bit of piston slap. The newer LT1's had a lot of this. If new mains and rod bearings didn't change it, either one of two things....
1-it is not bottom-end related, or
2-it is the crankshaft that is undersized.
Did you plastigauge the bearings when you put them in??
What weight of oil do you use??

[This message has been edited by Dave Birdwell (edited 11-19-99).]

[69-er]

Yeah, I guess it could be the pins or pistons. Since I didn't remove them, it would be kinda hard to check for wear. I know I couldn't "feel" any pin or piston skirt wear by moving the rod around while the crank was out.

Speaking of piston slap, I'm not sure I've ever heard it. My truck has an AutoZone motor in it and when I pulled it to do a gasket change, I found all kinds of wear, bad assembly, two sleeves, worn out valve guides, cracked and hard valve seals... That motor sounds like a diesel when it's cold. I thought that might be piston slap since who knows what else is wrong with that engine. In fact I had a motor years ago that had forged pistons and I believe it made the same noise until it warmed up and the pistons expanded to operating clearances.

I didn't check the bearing clearances since the bearings looked so good.

I've used Mobil 1 since new and since the teardown, Penzoil 10w-40. FYI, I read somewhere that Mobil 1 isn't too frendly with old style gasket materials. I guess it deteriorates them. But I know one thing, it didn't hurt the motor in the wear department! I never expected to see original machine marks on the cylinders and no ridge whatsoever.

Larry

[mccorry]

Possibly a motor mount? My wifes car had a mount that would bang when it was hot out. Just a guess....