Cracks in my head

[thescifiguy]

ON THE SUBJECT OF CRACKED CYLINDER HEADS:
I remember RallyBob telling me years ago that it was really hard to find Opel heads that weren't cracked. Something like 4 out of 5 had cracks. Now, I'm going to assume that most of these heads he ran across came from engines that didn't have any obvious running problems due to a cracked head. In other words, heads from okay running cars, before they were junked.

By extention, I interpret this all to mean that 4 out of 5 of us with original unrebuilt engines have cracks in our heads (a little joke tucked there).

So, this tells me that some cracks in your head isn't that serious a thing......most of the time. If 4 out of 5 of us have a few cracks in our heads and yet we're not stuck on the side of the road and we don't have mixing or leaking fluids, do we always have to reject a head with cracks when considering rebuilding one?

[jeff denton]

I kind of suspect Bob was referring to the later (twelve-bolt) heads as being prone to cracking. Somebody please correct me if wrong, but later heads were from 74-up.

[thescifiguy]

This all stems from discoveries made about my engine that I brought up in my 2 previous threads: "Pre-war engine? and "How long is your dipstick?".

In a nutshell, it's a pre-GT 1.9 engine with no year of manufacture on it and it has unusual power.

[wrench459]

I've found only one big crack in Opel heads.
It starts on number one exhaust guide and continues to number four exhaust guide right through the center of the head. Yep there out there and a plenty of them.

[GTJIM]

The late 1971 - early 1972 12-bolt (four cam bearing) heads were OK till Opel tried 'chilling' the valve seats during manufacture to harden the seats for unleaded fuel. The later fuel injection heads from 1975 on also seem to be better.

Late '72 through '74 heads with the 'chilled' valve seats are either cracked ... or going to be ... after just one overheating experience.

Small block Chevy heads of that era also had very similar valve seat problems for the same reason.