Why do M20 head(s) crack?

[HJ1981]

Hey guys,

I am currently saving up for a winter project, i plan to remove the rear subframe, reinforce it and get some alignment plates welded in.

Then i remembered that the PO installed a new AMC head on my car, he claims that it is more reliable than the factory 885 head which is known to crack.

As i researched this topic, it does appear that the factory head tends to crack at the camshaft lobs, more common on #4 and #5 locations.

I have spoken with many shops that specialize on these E30s, from full blown race cars to street cars. They ALL recommend the AMC head for reliability, and the risk factor of a used 885 head with unknown stress levels will eventually crack at some point.

Also researched how people claim that, the AMC head is thicker, less prone to cracking (sofar i found no one reporting a cracked AMC head) but the quality of the intake ports are questionable, when compared to the 885 head.

My question is, should i invest in a used 885 head to get that "all factory" engine, but then risk a crack developing sometime in the future (due to design i guess). Or stick with the AMC head and call it a day? It is worth the money, time and risk to go 885? or not?

Thanks

[BenHar]

They only crack if they overheat.

Ben

[Brianmoooore]

They only crack if they overheat.

Ben

Doesn't take much of an overheat to do so, though. I've only ever cracked one, and that was as a result of not being bled quite enough after a coolant change.

[HJ1981]

Are you guys certain of this? it is not due to the head being "too thin" when casted? i found that to pop up a lot on forums.

Also, i found a thread somewhere, where it is recommended to either enlarge or drill a new coolant passage hole on the gasket itself. Any info on that?

[Brianmoooore]

The design was flawed, as can be seen by the 'improved' AMC ones not being so susceptible to overheating, and casting methods weren't so precise in the '80's as they are now, so there were always some that were going to crack anyway, because of a thin stress point, but the great majority won't crack unless abused.
Don't forget that this abuse can be in the form of old, damaged radiators, cooling systems that don't pressurise properly, failed fan couplings, old or too dilute antifreeze, etc., as well as the obvious one of coolant loss.

[HJ1981]

The design was flawed, as can be seen by the 'improved' AMC ones not being so susceptible to overheating, and casting methods weren't so precise in the '80's as they are now, so there were always some that were going to crack anyway, because of a thin stress point, but the great majority won't crack unless abused.
Don't forget that this abuse can be in the form of old, damaged radiators, cooling systems that don't pressurise properly, failed fan couplings, old or too dilute antifreeze, etc., as well as the obvious one of coolant loss.

I pretty much took care of the entire cooling system (new rad, hoses, fan, switches, pump, t-stat etc).

So, it is worth hunting down an 885 head and swap out the AMC one?

[Brianmoooore]

That depends entirely on how much of an OEM type you are. AFAIK, there's no significant downside to the AMC head, and it is known to be more resistant to cooling system failures than the 885, so I'd be entirely happy to leave the AMC version in place, but I use Mondeo roll bar links, E46 steering racks, LPG as a fuel, etc. on any of my E30s that I intend to drive.

[HJ1981]

That depends entirely on how much of an OEM type you are. AFAIK, there's no significant downside to the AMC head, and it is known to be more resistant to cooling system failures than the 885, so I'd be entirely happy to leave the AMC version in place, but I use Mondeo roll bar links, E46 steering racks, LPG as a fuel, etc. on any of my E30s that I intend to drive.

Just wanted it to be reliable, as i dug up the only real downside to the AMC head is sometimes (not all) one see's poor casting quality on the intake ports. Also heard it is 3-4 mm shorter as well?

But everything else is the same, more or less.

[Brianmoooore]

I did originally write "that can't be cured by a few minutes with rotary burr" after "no significant downside to the AMC head", but then deleted it, since I have no practical experience of the AMC head that I'm aware of.

[HJ1981]

I did originally write "that can't be cured by a few minutes with rotary burr" after "no significant downside to the AMC head", but then deleted it, since I have no practical experience of the AMC head that I'm aware of.

I just do not wish to spend €500+ on a used solid 885 head, then another €600+ on BMW parts (rockers, hardware and such) and go through a new belt and the labour to replace the head, only to have it crack.

[flybynite]

I have spoken with many shops that specialize on these E30s, from full blown race cars to street cars. They ALL recommend the AMC head for reliability, and the risk factor of a used 885 head with unknown stress levels will eventually crack at some point.

Then I think you have your answer

Just wanted it to be reliable, as i dug up the only real downside to the AMC head is sometimes (not all) one see's poor casting quality on the intake ports. Also heard it is 3-4 mm shorter as well?

As it is the AMC head you already have then keep it. If you are finding problems with the head the cure those.

As Brian (was about to) say casting marks the ports can be easily sorted with a die grinder if that is causing you an issue.

[HJ1981]

I have spoken with many shops that specialize on these E30s, from full blown race cars to street cars. They ALL recommend the AMC head for reliability, and the risk factor of a used 885 head with unknown stress levels will eventually crack at some point.

Then I think you have your answer

Just wanted it to be reliable, as i dug up the only real downside to the AMC head is sometimes (not all) one see's poor casting quality on the intake ports. Also heard it is 3-4 mm shorter as well?

As it is the AMC head you already have then keep it. If you are finding problems with the head the cure those.

As Brian (was about to) say casting marks the ports can be easily sorted with a die grinder if that is causing you an issue.

Alright then, i do not have any issue(s) with the AMC head the PO installed, just how people's opinions where pounding my mind on the 885 head being "superior" to the AMC one, yet locally in Germany it is the other way around, wanted to hear your thoughts on this.