L18 with no compression

[sexyL]

Motor stopped running for unknown reasons. L18 with A87 peanut. Flat top pistons and shaved just a tiny bit (can't find the spec slip for it). Head was completely redone with new seats and valve job. Basically everything was new or redone.
So when I got digging into it, I've noticed these things:
Headgasket looked fine, no markings or any signs that it was blown.
Cylinder walls had no vertical score marks or noticable markings
Compression was something like 20-60-40-140. Only #4 would fire when turning it over.

At first I thought it was a blown HG since I did use a felpro (lol) with pretty high compression but it appears not. The car was running fine for at least 1000mi until one day I tried to start it and didn't work.

Any ideas on what to do? Usually I'd just go through the usual tests but kinda wanting to hear what people have to say.

[datzenmike]

Check the valve lash. New valve job... maybe they sank onto the seats a bit and there was no clearance. The valves may not have been tightly closed.

[okayfine]

How do the cam lobes look?

[sexyL]

Cam was a brand new Isky when I built it... they're still not fully "shiny" and don't look worn or anything.
There was, however, an early problem with the cam when I first put it together where Loctite was hiding in one of the lobe oiling holes causing that lobe to wear faster, but it's fixed and everything has an even look across the lobes.

[datzenmike]

Check the valve lash.

?

[bertvorgon]

Did it get really hot at any point? I took the ring tension out of my L-18 years ago, when the head got too hot from a high speed drive, and my stock radiator could'nt handle it.

High compression...low quality fuel...pinging...?

[sexyL]

Datzenmike- I'll have to check the valves tomorrow on my day off but will get back on that.

I don't recall any overheating. I'm running an aluminum VW radiator (the wide one). Lots of detonation actually, 91 octane with octane booster didn't really help. It seemed like no matter how many bottles of octane I put in it didn't help with the detonation that much. I wasn't running lean though.

[defdes]

Did the timing check out with all of that pinging? That doesn't sound right. You should be able to run 10.5:1 or so with 91 octane.
Before I had my race motor running properly, I had to re curve the distributor, and the cam timing was off too so instead of 220 compression, the figures were like 135psi across all 4.

[sexyL]

Actually forgot to mention: detonation only occurred right when i would open the throttle after idle. So for instance, I would be idling and when I start giving it gas it would detonate--Not so much at high RPMs or flooring it.

Maybe that's the problem? So then would I retard it a little bit? But I don't see how that would cause the pressure to drop to the 40s.. and why would only one cylinder be at 140?
Now that i think of it... I never took (or at least I remember taking) a pressure test on each of the cylinders when it was running. Damn. Perhaps I didn't have it at TDC when timing it?

[bertvorgon]

Detonation..if it is severe enough, and over a bit of time, can both compress your ring land(s), and/or break the rings, depending on the quality of said components. When that happens, the rings cannot do their job, so that is how the compression disappears. PINGING is the worst, at high load, the pressure can be HUGE, when you crack the throttle like that. And, just because you could not hear detonation when you are going, does not necessarily mean it was not pinging away in there, creating heat and stress. Not saying that is what happened in your case, but, you should be aware of that, if all other bug sorting does not show anything.
Regular Octane boosters are CRAP, and only raise octane by a decimal point..not FULL octane points!!!! Save your money and retard the timing to run on the available fuel. Trust me on this one, I have lived fuel and octane all my life, with my turbo motor.
As others said, check that cam timing first, seeing as how that thing was apart, as that setting will kill static compression readings, if off. Get that right, then check valve lash. Then spin motor over and do a test, with throttle(s) open. If you then get it to start, both retard your timing, and, re-jet to help cover the possible lean throttle opening.
Make sure your spark plugs are not too HOT either, as they can start pinging also.