Weird cylinder head question

Falkenberg · Post by **Falkenberg** » Sat Oct 04, 2014 4:32 pm

So I've been trying to put my 528 back together lately.
Today was engine day. Before I had an issue where a small part of the high-crown pistons were touching the head, since I was going to change the pistons anyway I did not give it much attention. But today when we wnated to put the head back on the rebuild engine, we observed that the new (E32-style) pistons hit the head badly. Then I started to look on the web for pictures and I notice that my head is different than others. See pictures. What is going on here? What should I bee looking for? Dremel or a different head?
Mine (notice the blue grease check of interference between piston and head):

20141004_016

Other found on the net:

THe head is not the cars' original, it is supposed to be an 528 head and has '81 casted on it.

Mike W. · Post by **Mike W.** » Sat Oct 04, 2014 8:39 pm

So you're using B35 pistons with an earlier head? I've heard both, that the pistons will clear and that they'll hit. Remember the head gasket is ~1.7MM thick so if you're measuring without it it's not a good measurement. If you do have to clearance something, I'd probably file the pistons, not work on the head. Check inside the crown, but I think you have plenty of meat there on the piston. And you don't need the full clearance, one BMW I had, a 733 I think, had pistons that were .4MM higher than the block, but the head gasket provided the clearance.

Falkenberg · Post by **Falkenberg** » Sun Oct 05, 2014 3:37 am

The block is now fitted with M30B30 pistons from a later motronic car:

20141004_013
You can see where the contact surface with the head is, where the blue grease has dissapeared. Test was done with gasket in place.

I'd rather not mill anything - and I thought, if forced to do so, that it would be easier to do the head, figuring that I don't want pistons of different weights..

But I'd still like to know what is with the head. Also the original 1976 M30B28 pistons hit it, but less (left one in picture, small mark on edge of crown):

Pistons

Do I have some kind of special cylinder head? Still can't find any pictures of something similar.

Falkenberg · Post by **Falkenberg** » Sun Oct 05, 2014 9:18 am

Today I dug up the cylinder head that was on the car when I bought it. It is in a sorry state, which why it was swapped in the first place.
Put one next to the other, bingo. Not the same:

20141005_002
One is an '79 old style water jackets, the 'wrong' one is an '81.

The '81 part number:

20141005_003

The numbers on the '79:

20141005_005

Could the '81 be a M30B25 head?

Falkenberg · Post by **Falkenberg** » Thu Oct 09, 2014 9:58 am

So I still have no idea where that cylinder head is coming from.

Meanwhile, I sourced an '89 motronic head that fits on those motronic pistons (the compression chambers actually look like the ones on the '79 head), I'll send it to a shop for rebuild an while there they will swap the cam so that it works with a distributor, and I'll put the weird cylinder head on a shelve in the basement.

JodyStevens · Post by **JodyStevens** » Thu Oct 09, 2014 11:03 am

I've never seen a head with that shape before either. Very odd.

Falkenberg · Post by **Falkenberg** » Fri Oct 10, 2014 4:09 am

I just found another one:
http://www.ebay.de/itm/BMW-E3-E9-E12-E2 ... true&rt=nc

Says in the picture that is from a '79 528, in BMWfans the newest I can find is a '77, but anyway, the part number listed there (11121262241) is for a cylinder head reserved for E12, E24 and E23 2.8 and 3.0 carburettor versions, starting from 08-1976 in case of the E12.
The 528i head has a different part number: 11121278702

I can't find the part number for the original head. It's just not listed in the catalogues, but for an 525 it is 11121250017 up to 08/76.

Put in order, things would be as follows for the 528:

Up to 08/1976 the 528 had Zenith INAT carbs, using the piston with the high crown (pic above) and a cylinder head that might have had part number 11121250017. This is apparently a very common head, used on E3, E9, E12 from 2.5 up to 3.3 engines. I could not find a picture, but I assume that combustion chamber shape is the common one. I wil know this for sure when we open up my friends E3 3.0si which needs an engine rebuild.

Then the E12 (and also E24 / E23) switched to Solex 4A1 carburettor, used the piano-top pistons with the slightly lower crown (pic above) , and switched to cylinder head with part number 11121262241 that has an atypical combustion chamber shape. I do have the pistons out of such an engine, the piano-top is lower, it might just work but I have not tested it.

Then 528 carb was phased out, only 528i remains, which used head number 11121278702. I found a pic on the net that suggests that this head had the common combustion chamber shape.

So something definitely is going on. Lesson learned: when using pistons with a crown, avoid the 75-81 carburettor cylinder head, which is possibly always paired with the Solex 4A1 carburettor, unless it is certain that the combination has worked before.

I have another '81 525 for parts, I suppose that it also has that weird head. I'll open it up when I have the time.