[69GPModJ]

I've noticed when starting my car that the engine has what sounds like a knock. The sound lasts until the engine is warm and then it seems to disappear.

I've changed the oil about 6 times since rebuilt (2,000 miles ago--long story why so often) and never found any excess material in the pan or in the filters (dual system). I'd characterize the stuff I find on the magnetic plug as a very fine powder. When I wipe it off the plug, it turns into a silver paste on my fingers. There isn't a lot of it either--maybe enough to cover three-quarters of my thumb print.

Here are some specs:

- Solid flat tappet cam with about 250 duration & 540 lift (rockers about 0.002" to 0.003" more play than recommended by cam manufacturer)
- HS roller rockers
- 0.025 clearance for both mains & rods
- side-to-side rod clearance checked out (though can't find the numbers anywhere)
- a bit more piston to cylinder clearance than normal, as I plan to run nitrous once in a while
- top ring gap of 0.022"
- bottom ring gap of 0.024"

I plan on using a mechanics stethoscope to have a closer listen but, in the meantime, any thoughts?

[69GPModJ]

I've noticed when starting my car that the engine has what sounds like a knock. The sound lasts until the engine is warm and then it seems to disappear.

I've changed the oil about 6 times since rebuilt (2,000 miles ago--long story why so often) and never found any excess material in the pan or in the filters (dual system). I'd characterize the stuff I find on the magnetic plug as a very fine powder. When I wipe it off the plug, it turns into a silver paste on my fingers. There isn't a lot of it either--maybe enough to cover three-quarters of my thumb print.

Here are some specs:

- Solid flat tappet cam with about 250 duration & 540 lift (rockers about 0.002" to 0.003" more play than recommended by cam manufacturer)
- HS roller rockers
- 0.025 clearance for both mains & rods
- side-to-side rod clearance checked out (though can't find the numbers anywhere)
- a bit more piston to cylinder clearance than normal, as I plan to run nitrous once in a while
- top ring gap of 0.022"
- bottom ring gap of 0.024"

I plan on using a mechanics stethoscope to have a closer listen but, in the meantime, any thoughts?

[David Jones]

Lifter adjustment.

[Lloyd-TX]

Sounds like cold piston slap to me.

Ever hear an older Hi-Perf forged piston chebbie engine upon cold start?

[69GPModJ]

"Cold piston slap" If that's what it is, can I "live" with it for a while or is it something I need to worry right now? I'll probably tear the engine down in a year or two anyway.

[bobzdar]

You can live with cold piston slap pretty much indefinately. Some new ls1 cars do it new from the factory. Given you have a solid cam, it could be that, check lash and if it's ok I'd ignore it as long as it doesn't do it when the engine is warm.

[69GPModJ]

Well, I finally got around to adjusting the valves. That isn't the problem. I've still got the noise.

Also, now I've listened to the engine cold and hot with a mechanic's stethoscope. The "knock" when cold is audible without the stethoscope. When hot, you can't hear a thing without the stethoscope. On the other hand, with the stethoscope you can hear a very slight knock at the #2 cylinder when you touch the block close to the pan. If you touch the block close to the pan on the #1 cylinder, you don't hear anything. When you listen close to the head, you can't hear a thing (except valve train noise).

Oil pressure is good--40lbs at idle, 60 to 65 cruising, and around 80 when you step on it. No debris in the oil or filters.

Thoughts?

I may pull the engine apart over the winter for peace of mind but don't really want to. That'll be the fourth time in a year I've pulled the engine.

[Doug Christie]

Your gonna tie my record Kerry! It's a pain in the @ss, but the "peace of mind" factor is worth it. Good luck.