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Back to my 2.3 rebuild.

I have 2 engines and have stripped them both. On both engines bores 1-5 are in perfect condition however #6 has signs of bore wear with a ridge at the top. The higher mileage engine had done 135k (allegedly), the head was very badly eroded (scrap) and there was a lot of sediment in the water jacket at the back.

The wear is only on one side of the bore next to the flywheel. I'd expect it to be symetrical or either side (L&R) but it's not. Has anyone seen this before, is it common on the e21, does it perhaps mean that #6 was running a bit warm? I've dismantled quite a few e30 2.5s and never seen this before, in fact I've never seen any real bore wear on an M20 until today.

Just wondering if anyone has seen this before or knows the cause?

In most cases you see wear, loss of compression, etc more often on cylinders 5 and 6, and as far as I know that indeed has to do with the fact that this is the hot side of the engine. Near the firewall picking up heat from the exhaust manifold and getting the least cold air from the front.

Cylinders 1-5 are perfect, no sign of wear at all, I can only put it down to localised overheating as you suggest. Guess I'll have to use the other block that has no wear then!