Sounds like the same basic thing that happened to me last year. Bad gas caused detonation, and broke a land on the #4 piston. The broken bits stayed in place luckily.
Pull the pcv out (if you are using one) when the engine is running to get an idea on the amount of blowby. If is a lot chances are it is a broken piston.
Sorry Tommy

Never knew what a leak down test was, so I googled it.

Leak-down tester - Wikipedia, the free encyclopedia

Sounds like rings or piston. You need to get the valve train geometry correct either way.

Update: Two steps forward and one step back.

Thanks for all the comments and suggestions. For those suggesting a leak down test - I agree. But I haven't yet gotten my hands on the equipment to do that. For those suggesting I deal with the rich condition - I agree. I'll start that after I deal with the noise from cylinder 8. Here's what happened today.

I buttoned up the engine and ran it for 30 seconds or so to burn out the oil in cylinder 8. Other than a cloud of smoke coming from the driver's side exhaust, it ran normally. I then pulled all the plugs and repeated the compression test. Cylinder 8 showed a good 210 PSI with the oil gone. I drained and changed the oil and oil filter. The old oil looked normal and there were only the usual fine iron filings on the magnetic drain plugs. With the plugs replaced, I ran the engine at idle until the water temp came up and all seemed normal. I then increased the RPM slowly to see if either the noise or KNOCK ALERT light would appear. Everything was alright until I reached about 3,500 RPM. At that point, a lot of smoke began to come from the driver's side exhaust and I shut it down.

An optimist would say the smoke was merely residual oil from the cylinder 8 test that had made its way into the exhaust and had finally gotten hot enough to produce smoke. A pessimist would say I had not found the root cause of the problem and it reappeared when the RPM got high enough. I say I've got too much to do for the next few days to deal with it now. I'll check it out the first of next week and see what I find.

Could it be a crack in the block or head that requires a certain amount of heat to open up?

i would guess now that your intake runner on #8 is not sealed and allowing crankcase oil to enter. or something similar. on initial startup the crankcase doesn't have the oil fog, after warmup and possibly things move around it starts sucking oil vapor. also check the exhaust and intake valve seal.

Final Report (assuming nothing new pops up)

First, thanks again to all who took time to read and comment on my problem. I appreciate you all.

I ran the engine long enough to finish burning all the test oil from the exhaust and then rechecked cylinder 8. The spark plug looked fine and the compression was still above 200 PSI. So I took it for a 40 mile test ride averaging 2500 RPM or so. There were no unusual sounds, no unusual KNOCK ALERT warnings, and no smoke from the exhaust. So far as I can tell, everything is back as it should be.

The only substantial things I did to solve the problem were reset the lifter preload and install new spark plugs. My best guess is that some combination of old plugs, and insufficient valve opening on cylinder 8 caused that cylinder to not combust properly.

I added a dose of Sea Foam additive to the gas to help remove any carbon deposits on the valves and unstick the float valve if it is sometimes sticking. I'll be checking the spark plugs regularly to see if symptoms of the rich condition return. After the Sea Foam runs through, I'll also recheck the lifter preloads to see if carbon buildup on the valves contributed to the low preloads. If the preloads are still too low, I plan to get some slightly longer pushrods so the preloads can be set correctly.

Tommy


have you measured the tappet lift on the cam??? you could be losing a cam lobe, especially with the comment about metal on the drain plug magnet----