Engine won't turn over -- please help with diagnosis

[o0sara0o]

1979 Spider. This vehicle was rescued from a field under a tattered tarp. BUT we had it running a year ago, even drove it around the block, and have been working on the body since then.

Now, the starter can't turn over the engine. One turn, stop. One turn, stop. Totally weak. With jumper cables to another running vehicle, it dims the lights of the other car, but still nothing.

Strange, maybe relevant fact: when trying to push-start, popping the clutch out seems to be the equivalent of slamming on the brakes. Rear wheels will skid and jump before the engine will turn over. Tried in 1st, 2nd, and 3rd gear. In 2nd, it literally pops the gearshift back into neutral.

OK, engine seized? Nope. Engine will turn over--weakly--when spark plugs are pulled out. Besides, the last time it ran, it drove us around the block with some pep.

We attempted to pull out the starter, and gave up. &$^#&@ those Italian engineers. Someone on this forum had suggested a possible interference issue, so while we were in there, we replaced the timing belt and made sure the timing was all proper.

If the starter were bad, shouldn't we be able to push-start it without any trouble?

Is it possible that there is a valve stuck open, and a piston is hitting it?

What else should we consider?

Thanks for any insight.

[wizard124]

Have you put some oil down the cylinders? Let soak and try to crank it w/out the spark plugs in. Any rust on the plugs or evidence of water intrusion into the cylinders from a warped or cracked head? Does the oil on the end of the dip stick look contaminated?

Maybe a bad battery. Hookup a known good battery or disconnect the battery and try jumping it again.

[So Cal Mark]

I'd turn the engine by hand at this point, and stop if you incur interference.

[o0sara0o]

Thanks for suggestions. Already tried putting oil in cylinders. No evidence of rust on plugs. Oil seems good. Tried cranking with known good battery. Turned by hand several times while replacing timing belt (and double-checked that timing was correct. There was always a place every half turn that was a little tougher, but it didn't take much more effort; I figured that was just overcoming TDC.)

With no other clue what to think, I suspect that the best possible scenario is a combination of several problems: battery is kaput, starter is weak and/or dying, engine is still atrophied from years of sitting. But shoot, it ran so well there a year ago... Is jumpstarting so troublesome? A big guy like me should be able to get that little car turning over fairly easily in 2nd gear, no?

[So Cal Mark]

tdc isn't that hard to overcome. I'd expect you have a bent valve now