So, 1982 Corvette, Edelbrock ProFlo4, 256 Voodoo Cam, 72 cc Dart SHP heads, Forged flat top pistons,roughly 9.5 : 1 compression. 1.6:1 roller rockers built in 2014. Was riding with a friend, really got on it. Then it just died. 5000 rpm to 0 no tach even with the clutch out. Got it home, popped off the timing cover, and the crank gear had one tooth left. Found all the others in the oil pan. No glitter in the oil. (yeah, surprised me, too). Used a scope to peek inside all 8 piston bores. Dude you can still see the cross hatching on the walls. Valves were all seated (I had backed off all 16 rockers) no visible signs of damage to any pistons. Installed new timing set, this time went with a double roller. Engine spins fine by hand. Got everything lined up, start it, and it sounds terrrible. No knocks, no pings, no clunks, just sounds like timing is off. Tear it back apart and re check timing gears, re install anyway to be double sure. Buttoned her up and tried again. It ran about the same. The IAC stays above 75%, and it actually runs smoother with the pcv and brake booster ports un capped. While it was running I checked the valve lash (hydraulic flat tappet) backed off until they start tapping, then tightened till no noise plus a 1/4 turn. #4 exhaust never made noise, not a single tap. I loosened until the rocker stopped rocking, no tapping. So I am thinking collapsed lifter. Pulled the intake today, all the lifters look good. What is a good way to test a lifter outside of the motor? Also, am I overlooking something? I have not as of yet pulled the heads because of the scope images. I'm not thinking cam, because the rockers were all moving when I ran it with the valve covers off and the previously mentioned lack of glitter in the oil pan. I pulled both lifters on #4 one at a time, and they looked fine, and the wear pattern was normal on both lifters. Honestly they didn't have a lot of wear at all. I have run Mobil One and the zddp additive since the first oil change after break in, I think that is why the insides look so good.

Checked timing multiple times, re stabbed the distributor twice to be sure. Also verified all the plug wires were in the right place. Installed new plugs as well. It will not run smoothly with all the vacuum ports connected. It wants a ton of air. I am looking to pull heads next to verify what I saw with the scope. I am totally at a loss. I showed the gear to a mechanic friend and he said it looked like a bad heat treat that finally failed. There is nothing that I can feel or see that is impeding the rotation of the motor. Something is damaged, it could well be the lifter, but other than putting in a new lifter, how do I verify that the lifter is good? Have any of you had a similar thing happen to them? Any help would be greatly appreciated.

 

use an adapter and plug an air hose into the spark plug hole as a quick check to see if the valves really are seated, you'll hear it coming out at the carb or exhaust if one is not seated due to being bent.
Or do a compressions test.

 

Did that on #6, the rest are a bear to get to. #6 is good, though. Got the scope when the spark plug holes got so difficult to thread the adapter into. The intake is currently off, so I'll look down the runners of the heads to see what I can see as far as the intake valves.

The intake valves look pretty straight. Lots of carbon, but straight. I think I am gonna add a catch can to the pcv line. It's pulling a lot of oil.

 

You mentioned you checked timing multiple times. What did you come up with for a number? Do you have ignition timing control with your EFI or do you have a mechanical and vacuum advance?

 

Mostly I do not like that #4 would not "rattle" when loosened.
Something is wrong in that cylinder.
Without pulling heads, I would check cranking compression, and leak-down, and report back.
Buy a ~$100 leak down gauge, it is much better than compression. But if your compression is not good, you already know.
Valves may look seated, but you could have bent one. That would explain the sticking #4 too.
Hopefully it is just a bad sticking lifter.

Was this a metal crank gear that sheared off teeth? or the OEM plastic tooth one?

 

How in the world would that even be possible? Loosen "until the rocker stopped rocking" and no clatter? That rocker should be bouncing around all over the place at that point and making a racket.

 

The base timing is supposed to be set at 12 deg, and as rough as it runs, it is steady at 12. The next step in the set up process is to get the IAC set between 5% and 15%. I cannot get it below 70% and usually it sits at 90 to 100 %. The distributor has a hall effect sensor, so the efi system controls spark timing as well.

 

I agree, it defies logic. Right now the intake is off the motor. I don't want to re install the intake just to test compression. I'm thinking I might as well pull that head and see what I see. That rocker not tapping was definitely concerning.

It was a metal crank gear that failed, snapped the chain as well.

 

No tick. No rattle, nothing. So i just tightened it back up until it started opening the valve again and then I shut down the engine. I was sure it was a collapsed lifter, but it doesn't look collapsed. I'll take some pictures tomorrow and post them here maybe y'all will see something I don't.

 

I would be concerned with the #4 cylinder also..

 

You do not need an intake to run a compression test. Just the valvetrain all hooked up to seal the cylinder.

Start with the basics. Confirm what's good. Then move on.

Something bad happened inside to snap a timing chain and a metal crank gear.