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.



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[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!

[Rosanante]

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

The M90 engine is an odd hybrid. It was created when BMW was testing out the M88 (which used a 24 valve DOHC head). They simply put the existing 12 valve SOHC head on the new block and bottom end. It worked surprisingly well. Dubbed M90, they used this in the early 6 series cars. As a result I rather doubt that the cylinder head, which really is unrelated to anything that makes and M90 different from an M30, would be marked in some way unique to that block.

Here is an excerpt from an article "History of the S38 Engine" by: Raymond Woertman IIRC this was on the First Fives web site, or some such place.

"The engine for the ///M1 was an evolution of the M49 engine of which the development stopped in 1977. However the new M88 was spend with significant changes to allow also to be used as a production engine for road cars. This was necessary to sell the E26 ///M1 as a road car, a requirement for the group 4 regulations. The Group 4 rules required that 400 units of that same car would be made within one year. The direct drive of the camshafts by a gear train was abandoned for a direct chain drive to reduce the interior noise. Like the M49, the M88 engine also used a Kugelfisher mechanical fuel injection system. The cylinder head of the M88 consisted of two pieces. The lower piece contained the intake and exhaust ports, the valves and the spark plugs. The upper piece contains the buckets, shims, camshafts and bearings

Compared to the M49/3, the M88 had a slightly smaller displacement (3453cc). This was achieved by reducing the bore slightly to 93,4mm. However the stroke of the engine remained the same (84,0mm). To test if the M88 engine would be reliable for a production engine, BMW placed the existing SOHC drive train on the M88 cylinder block. This engine, called M90 used a regular Bosch L-Jetronic (predecessor of the Motronic) fuel injection system and yielded 218hp."

So, presumably the block would also not be marked with any sort of M90 designation because it is really an M88 block... I'm also not sure the "84" on the block is a date code. It might be, and if so, then the block would not be an M90, but instead an M30 (longer stroke, smaller bore). From what I have read, not all engines were stamped with the vehicle VIN, so unless there is visible evidence of someone grinding off the VIN (that would presumably be very obvious), the lack of a VIN would not be very indicative of anything.

Other ways to tell.. You can put it on a dyno and see what it makes. You can pull the head and measure the bore. You can pull the pan (easier said than done in the car) and measure the stroke...

I am also unconvinced that the turbo sticker tells us anything of note. Folks put stickers of all types on cars. I've even seen a BMW roundel on a Pontiac...

Changing an 84 non L-Jet engine to L-Jet would be a big messy job, and I am not sure it would do anything of benefit, so the fact that it is an L-Jet probably indicates it is either an M90, or it is an early 3.3 liter M30.

My best guess is that if the "84" on the head is a date code, then the PO probably swapped an 84 head on an M90 block, and used the same old intake and L-Jet hardware he had. To me, that's the most plausible situation.

[jmile46]

The M90 engine is an odd hybrid. It was created when BMW was testing out the M88 (which used a 24 valve DOHC head). They simply put the existing 12 valve SOHC head on the new block and bottom end. It worked surprisingly well. Dubbed M90, they used this in the early 6 series cars. As a result I rather doubt that the cylinder head, which really is unrelated to anything that makes and M90 different from an M30, would be marked in some way unique to that block.

Here is an excerpt from an article "History of the S38 Engine" by: Raymond Woertman IIRC this was on the First Fives web site, or some such place.

"The engine for the ///M1 was an evolution of the M49 engine of which the development stopped in 1977. However the new M88 was spend with significant changes to allow also to be used as a production engine for road cars. This was necessary to sell the E26 ///M1 as a road car, a requirement for the group 4 regulations. The Group 4 rules required that 400 units of that same car would be made within one year. The direct drive of the camshafts by a gear train was abandoned for a direct chain drive to reduce the interior noise. Like the M49, the M88 engine also used a Kugelfisher mechanical fuel injection system. The cylinder head of the M88 consisted of two pieces. The lower piece contained the intake and exhaust ports, the valves and the spark plugs. The upper piece contains the buckets, shims, camshafts and bearings

Compared to the M49/3, the M88 had a slightly smaller displacement (3453cc). This was achieved by reducing the bore slightly to 93,4mm. However the stroke of the engine remained the same (84,0mm). To test if the M88 engine would be reliable for a production engine, BMW placed the existing SOHC drive train on the M88 cylinder block. This engine, called M90 used a regular Bosch L-Jetronic (predecessor of the Motronic) fuel injection system and yielded 218hp."

So, presumably the block would also not be marked with any sort of M90 designation because it is really an M88 block... I'm also not sure the "84" on the block is a date code. It might be, and if so, then the block would not be an M90, but instead an M30 (longer stroke, smaller bore). From what I have read, not all engines were stamped with the vehicle VIN, so unless there is visible evidence of someone grinding off the VIN (that would presumably be very obvious), the lack of a VIN would not be very indicative of anything.

Other ways to tell.. You can put it on a dyno and see what it makes. You can pull the head and measure the bore. You can pull the pan (easier said than done in the car) and measure the stroke...

I am also unconvinced that the turbo sticker tells us anything of note. Folks put stickers of all types on cars. I've even seen a BMW roundel on a Pontiac...

Changing an 84 non L-Jet engine to L-Jet would be a big messy job, and I am not sure it would do anything of benefit, so the fact that it is an L-Jet probably indicates it is either an M90, or it is an early 3.3 liter M30.

My best guess is that if the "84" on the head is a date code, then the PO probably swapped an 84 head on an M90 block, and used the same old intake and L-Jet hardware he had. To me, that's the most plausible situation.

Thanks for all the info!
So to start,
This car came with all the hardy& beck records from back in the day showing that it was specced with their turbo kit, so its not a matter of just decals.
But anyway, the plausible answer you speak of is the correct one from further digging. I put a borroscope inside and sure enough flat top pistons, which are an indicator of an M90. Block numbers match, date stamp adds up, and pistons match. Being a 528 it is still using all its original L jet components, so head is probably any old m30 head.

[Rosanante]

Thanks for all the info!
So to start,
This car came with all the hardy& beck records from back in the day showing that it was specced with their turbo kit, so its not a matter of just decals.
But anyway, the plausible answer you speak of is the correct one from further digging. I put a borroscope inside and sure enough flat top pistons, which are an indicator of an M90. Block numbers match, date stamp adds up, and pistons match. Being a 528 it is still using all its original L jet components, so head is probably any old m30 head.

OK, So presumably the head had an issue, maybe from the turbo, and they replaced it. Probably OK since, As I said, there was no specific M90 head. The M90 engine was an M88 with a SOHC M30 head...so pretty much any M30 head should do.

Good work with the Borescope!

Scott