M90 identification, its been a while…

[jmile46]

Hey all, I decided to come to the OGs for this topic because if anyone will have answers its you guys. Hoping Bert is still hanging out in here too, its been a while since we’ve had an M90 vs m30 identification thread.
So long story short, Ive acquired an alleged M90 powered E12 on BAT, and there was some people questioning if it was actually an m90 because it lacks the raised water jacket and the L on driver side of block, however Bert told us that late m90s didn’t have this. So I have come ready with all pictures of all stampings on not only this engine, but also my Euro imported 1985 635csi for comparisons.
So this block has all the stampings that alleged M90s should have given fellow members descriptions(1270006, and a manufacturer stamp of 3M 80 it appears, as well as the 3,5.) The cylinder head on the other hand is date stamped 84, which is a red flag, yet further down it is stamped 3,5 as well and wears the numbers 1304473, which a pdf from a member mentions to be an m90 head.
My Euro 85 635csi block wears the same 3,5 but the stamps above ac compressor are different reading 1287639. The head also wears different numbers reading 1277358. But an 84 date as well, yet no 3,5.
So my head on the alleged m90 certainly reads different numbers than the b34 head and rocks a 3,5(which what Bmw m30 era engine came as a 3.5 with early L jet style distributor?) but the 84 date stamp doesn’t make sense. Any and all insights appreciated!! Here are pics!
Alleged M90 head:



Alleged M90 block:


M30B34 from 85 635csi


And for fun my 89 M30B35 head

[jmile46]

Here is forum member provided pdf pictures showing their M90s identification features.



Sent from my iPhone using Tapatalk

[Bert Poliakoff]

So to make it simple, look on the engine block right above the starter. It should have the vin# of the car it came out of. Check that out. There are sites where you can find out for free, I just can't recall one now.If it came out of a model '82 or older, it has to be an M90 as in the early years only the Euro cars had 3.5's , Model year 1982 prior to May construction was the last year of the M90. Oh, there should be a number of 9.4 stamped on the flat tops of the pistons. 9.4 being the true compression ratio of an M90.The tops should be flat. If they have a piano shaped dome, it is from a later car or has been rebuilt You have some weird stuff there. If the engine uses a conventional distributor and is a 3.5 with Ljet, if a pre 81 car it should have the raised water passages and the stenciled L on the drivers side of the block. if post May of 81, the car should have first year Motronic 1.0. I am beginning to think that someone cobbled that motor together. And how can a motor supposedly an 81 at the latest have a head marked 1984

[jmile46]

So to make it simple, look on the engine block right above the starter. It should have the vin# of the car it came out of. Check that out. There are sites where you can find out for free, I just can't recall one now.If it came out of a model '82 or older, it has to be an M90 as in the early years only the Euro cars had 3.5's , Model year 1982 prior to May construction was the last year of the M90. Oh, there should be a number of 9.4 stamped on the flat tops of the pistons. 9.4 being the true compression ratio of an M90.The tops should be flat. If they have a piano shaped dome, it is from a later car or has been rebuilt You have some weird stuff there. If the engine uses a conventional distributor and is a 3.5 with Ljet, if a pre 81 car it should have the raised water passages and the stenciled L on the drivers side of the block. if post May of 81, the car should have first year Motronic 1.0. I am beginning to think that someone cobbled that motor together. And how can a motor supposedly an 81 at the latest have a head marked 1984

Just the man I wanted to hear from. Sorry I should’ve added, to make our lives difficult someone over the years grounded off the vin engraving above the starter, so a no go for identifying it that way. This car is what I believe to be utilizing the 1980 528i L jet management( the car’s stock management(down to the ecu). And another funny story is that this is actually one of the Hardy&beck turbo cars from back in the day as the “H&B Turbo” decal left a mark in the paint, so it’s been in some crafty hands. I guess Ill try and get myself a borroscope one day.

[Bert Poliakoff]

Well Ljet was used on the Euro 635s until May of 81 when Motronic 1.0 came out. So to stir the pot a bit, if your motor has a head dated '84 why would they, run Ljet when Motronic was available? Too many ifs with this motor. Looks like the only way to tell is to pull the head and measure the bore and look for the piston stampings. I can tell you I am running a well modified M90 on Motronic 1.0 and it seems to be doing well...but I won't really know till I get it on a dyno which is in the near future

[jmile46]

Well Ljet was used on the Euro 635s until May of 81 when Motronic 1.0 came out. So to stir the pot a bit, if your motor has a head dated '84 why would they, run Ljet when Motronic was available? Too many ifs with this motor. Looks like the only way to tell is to pull the head and measure the bore and look for the piston stampings. I can tell you I am running a well modified M90 on Motronic 1.0 and it seems to be doing well...but I won't really know till I get it on a dyno which is in the near future

Certainly a weird setup, maybe one day Ill pull it apart for a definitive answer. Thanks for the input!