Differences between m90 motors

[fidosd9]

While i was taking out the m90 out my 78 530, I found differences between two m90 motors i have. The one in the car painted blue is out of a 78 635 and is a dual row timing chain and it has 3z stamped on the block, and the block looks thicker where the water plugs go compared to the one out of a 79 735 L painted on with 2z stamped on. This one is a single row timing chain both have 93.35 stamped on the pistons i wonder why they did that. I am going to convert it to motronic 1.3 using the L-jet intake. I am going to need info on rebuilding either motor if anybody could help it would be great. Thanks for reading.

[thomas_m535i]

Could you be more specific on what kind of info about rebuilding your engine you're exactly looking for? About L-jet to Motronic conversion: there are FAQ's about this (http://www.firstfives.org/motronic.html).

FYI, some background info: I'm quite certain that only the Euro E24 635csi (<1981), some very early E23 735i's, and the E12 M535i had this type of engine block originally mounted. These were always 3,5L (3453cc) 6-cyl. engine blocks.
The 93,35 (+/- 93,4) mm is of course the bore, stroke would be (for a M90) 84mm.

At this moment, I'm rebuilding my M90 engine and when comparing it with what I see on your pictures, although also being 3,5L, I can see the differences. For example, the design of the block is slightly different and M90 engines never had dual row timing chains installed (as far as I know). I believe that your engine is one of the later 3,5L 'big block' 6-cylinder engines. These were designated 'M30'.

[Mike W.]

The top bolt oil filter points towards being an early engine, the pistons are flat tops, which are at least not the late euro 3.5 and while I don't know on M90s specifically, in M10 and M30s BMW used a dual row timing chain until 79 model year. 79 and later got single row, but if it was out of an E24 and went strictly by model year it could be from as early as 5-78 or 6-78 production as they started model year very early in the calendar year.

[Adam W in MN]

Interesting with the dual row timing chain. Do you have any pictures of the bottom of the engine blocks near the oil pan? I would like to see the casting of the bottom end to see if there are differences.