M30B28: bore to 89mm

[Falkenberg]

I kind of like the Zeniths, mine don't lose their settings and it is always funny to see the look on peoples faces when I open the hood

Suggestion 2 would be ok as well, but I have not seen such pistons on Ebay and I am looking for some time.
Suggestion 3 has disadvantages as well, what if the fit is not good? You get the same kind of overheating problems, so I've been told.

Below you have some pictures with my most troublesome cylinder. As a bonus, I added a picture of a bearing and a picture showing what it did to spark plugs.

[DEMIURGE]

I saw second oversize pistons 86.50 mm on eBay (Germany) - for only 50 Euro (all the six pistons). It was maybe seven-eight months ago.
As for the third suggestion - I'm sure - it works fine (I have such engine) - without any sign of overheating. I use the original old e28 pistons with new rings and after the first 800 km - fully synthetic oil. And for sure - the cooling of such block (you can say, with double thin walls) is better, then only one thin wall (for example 4.5 mm), but a very little worse, compare to the stock.

Of course I can't see how badly is worn the cylinder on the picture, even at 16 megapixel , but if you can feel the edge with fingers - it is not so good.
The best way is measurement. My case was much worse - I had no edge on the top of the walls, but I had very serious vertical grooves, caused by a very-very poor job (sharp edges on some rings after gap adjustment) of a "professional". Very unpleasant case

[Falkenberg]

I think I saw that auction as well, but one piston was missing a piece..

I can feel an edge in all cylinders, and you can see the strange damage in the picture to cylinder #3.

Compression figures were these:
Cylinder 1: 13,1 bar
Cylinder 2: 12,0 bar
Cylinder 3: 11,5 bar (this is the one in the picture)
Cylinder 4: 13,9 bar
Cylinder 5: 14,1 bar
Cylinder 6: 14,1 bar

So basically I have 3 decent cylinders, the other ones are shot. This is (I assume) because the carburetor feeding the first 3 cylinders had the choke blocked.

[DEMIURGE]

If you tell me - the compression figures are around 12 bar - I'll say - it is normal. It is very strange to have 14.1 bar compression in such engine. As for me - these numbers are too high.
However, the bad thing is, when you have big difference in the compression figures - in your case from 11.5 to 14.1...

With a little luck - you can buy M30B35 for 300-400 Euro. In Germany you can find whole e32 735 for 800-1000 Euro.
I bought my B35 engine for 300 Euro. It was in very good shape except two broken rockers (on the third cylinder both) and damaged camshaft - on the third cylinder again. Then I bought a e34 535 second hand camshaft in perfect condidtion from Austria (eBay) for 60 Euro and two new rockers for 15 Euro each (again from German eBay, NOS original BMW, not Febi or something similar aftermarket). So I can say - the total price is 400 Euro (not including the shipment for 150 + 40 Euro).

[Falkenberg]

Yes, the differences in the numbers are the problem. The scale might be off, it is new though, Draper.

[Mike W.]

.. bulges ..

I just was looking at a picture of an M30 block:

The lower vertical 'bulges' are the ones you are referring to?

Yes, that's exactly what I'm referring to. The earlier 3.0 blocks were smooth, the later 3.3 had the bulges, along with later 2.5/2.8 blocks even though they never used that bore with a long stroke crank. I finally got a pic too, but yours is much better.

[Falkenberg]

Thanks for the confirmation. I don't have those on my block, indeed. I have the 'water channel' early block.

[Falkenberg]

Winter has come. This is how the old beast starts after a -16 centigrade night: