Using 731 head compared to standard 200 head

[Atle_323i]

After having 200 heads fail on two occasions due to cracks under the cams I gave up and fitted a 731 head. There were no problems at all with this install other than the inlet ports being larger, so I used the e30 gaskets.

I had 3x 200 heads in my stock, two had visible cracks under the camshaft, the third looked good, I even had it crack tested but it also failed, I believe the action of just torquing down the head can cause it to crack from my experience.

Incidentally when building a 2.7 its the 855 head which is preferred.

Is the 731 head more durable than the 200 head, when it comes to crack, or is it just the same head quality?

[hans25]

The 731 and 200 cylinder heads, found on BMW M20 engines, are generally considered to have the same level of durability when it comes to cracking.

[e21Keith]

Maybe, but that's not my experience. I've seen three cracked 200 heads, zero cracked 731 heads and zero 885 heads. I've owned over 30 BMWs with the M20 engine.

[uwbuurman]

Well, that 885 head will crack. Mine did. A little bit of over heating and it was gone.

I bought an AMC head. Those are thicker and more solid. There are a few forums on the internet that discuss the differences between them

[Atle_323i]

Thanks alot for all the feed back guys. I learned alot about different heads etc for M20 engines.

[Atle_323i]

I bought the 731 head I had on hand, to prepare for use on my engine.
But I have tried to google specs on the 731 head, when it comes to thickness etc, to try to figure out if the head has been worked on before, or if it is in original state.

Google says (Gemini) says that the head is 125.1mm when new. And Chatgpt says the head is 126mm when new.
Does anyone have the spec for the head?

[Duracel79]

I'm not sure on the actual heights, but I believe all heads are the same height when new.

There are dimples in the head face which disappear when the head is machined over a set amount.
Not sure if the dimple depth correlates to being too much for a standard gasket (1.75mm ~ 0.069") or the thicker gasket (0.081" ~ 2.06mm).
Both gaskets should still be available to buy.

HTH

Ben

[Atle_323i]

I'm not sure on the actual heights, but I believe all heads are the same height when new.

There are dimples in the head face which disappear when the head is machined over a set amount.
Not sure if the dimple depth correlates to being too much for a standard gasket (1.75mm ~ 0.069") or the thicker gasket (0.081" ~ 2.06mm).
Both gaskets should still be available to buy.

HTH

Ben

I'm going for standard headgasket, 1,88mm. The head apears not to have machined many times. The dimples is far from gone. So a standard headgasket should be ok.