M90 Engine Or Not?

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thehackmechanic
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M90 Engine Or Not?

Post by thehackmechanic »

I hate to be yet another "does my car have an M90 engine?" poster, but I can't figure this out.

The car is a '79 Euro 635CSi, VIN 5546816 with 218,000 miles on it. It lost its dogleg close-ratio gearbox sometime in the past, and looks like it had been crashed, and doesn't have the tread-peeling torque I've read about M90s cranking out, so it certainly wouldn't surprise me if it no longer had the original M90 motor or ANY M90 motor. I read all the posts about M90 identification, looked for the raised water jacket and the big white "L," and didn't see them, so I just assumed that it was wearing some U.S.-spec motor from an early 633CSi or 733i with the dirty exhaust (no oxygen sensor or catalytic converter) bolted on. It IS still wearing the oil filter plate with the plumbing that runs to the oil cooler.

Then, during a recent valve adjustment, I noticed that it has a single-row timing chain. That seems to nail it as being an M90. It sure isn't an M88 :^). I also saw Bert Polikoff's posts about his late-production M90 not having the raised water jacket.

So I dug a little deeper.

The stamp on the block above the starter motor reads 41993529. This post here on the E9Coupe forum (https://e9coupe.com/forum/threads/is-th ... datTWxxaR8) says:

"As far as I know (please correct me if something is wrong)...
all M90s from E24s have the "3.5" cast on the left side of the block AND a VIN where the last seven digits start with 55
all M90s from E12s [meaning M535is] have the "3.5" cast on the left side of the block AND a VIN where the last seven digits start with 41"

but I haven't seen this corroborated anywhere else.

It's interesting that a '79 car with a 7-digit VIN has block stamp without the 7-digit VIN, but looking on this site and others, the changeover for when the blocks changed from using the VIN to an 8-digit number with engine code, daily production number, and date code is murky.

The casting on the head is 1277358 with an "84" date casting. I've seen the 1277358 head casting correlated to M90, M30B34, and M30B35 engines. With an '84 date stamp, clearly the head isn't original to the car.

What do you think?

--Rob Siegel
Author of eight books available on Amazon or at www.robsiegel.com

1979 Euro 635CSi
1972 2002tii, 1973 2002
1973 3.0CSi
1972 Bavaria
1999 Z3M Coupe, 1999 Z3
1974 Lotus Europa TCS
marc79euro645
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Re: M90 Engine Or Not?

Post by marc79euro645 »

I had an m90 in my 79 euro, also with the dogleg, when I got it 20 years ago. I guess it was ok for an na motor of that time with higher compression ratio than the m30s. I've since swapped to an 84 m106 with a 265/5 od tranny. I like the od tranny better than the dogleg, as 1st always felt too low and ran out quickly. My vin starts with 55 ,but I don't have the old m90 block anymore so not sure about the stamping. Mine did have the white "L" stenciled on the driver side.
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Ralph in Socal
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Re: M90 Engine Or Not?

Post by Ralph in Socal »

Pic below of motor I pulled from an early 635 with dogleg. Motor is M90 as confirmed by flat top pistons and 94 mm bore

I can’t provide doubtless confirmation of the “55” prefix but this motor does support it

Ralph
E0120E9D-E0BD-4A75-B4B7-441A78DA6CD3.jpeg
E0120E9D-E0BD-4A75-B4B7-441A78DA6CD3.jpeg (225.58 KiB) Viewed 6447 times
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85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
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jps635
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Re: M90 Engine Or Not?

Post by jps635 »

Hopefully you can open both attached pdf's

These are the identifying marks of a supposed M30 I purchased turned out to be a M90. Actually had M90 embossed on front end of head
Attachments
M90 -2.pdf
(1.31 MiB) Downloaded 305 times
M90.pdf
(1.4 MiB) Downloaded 292 times
'85 635csi JPS (RA2-66)
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.4) willbe stamped in the pston top.If the head is swapped out, which it obviously has, it will be missing the external

Post by bpoliakoff »

If you pull the head the piston size and compression ratio (9.4:1) What injection system and what number ecu? Regular distributor or front driven> My 81 euro is ``100% original and does not have external water `passage Bottom line is a 79 M90 will have external water passage and an external metal water pipe running alongside the head. I believe you have a plain old B34. M90 uses a single row timing chain
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.
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zinnocoupe
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Re: M90 Engine Or Not?

Post by zinnocoupe »

Like Bert says his 81 doesnt have the raised water jacket but I think all early ( like your 79) M90s have the raised jacket and 3.5 embossed. My 79 635 has the raised water jacket, white L and my Vin is 5547084. I would say the engine has been changed out for an NA b34. Unless you've missed the jacket and 3.5. Rob, is this the Polaris Euro you bought about 5 years ago?
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thehackmechanic
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Re: M90 Engine Or Not?

Post by thehackmechanic »

Yes, this is that car. I'm considering selling it, and want to get the story as straight as possible so I can say definitively what engine is in it.

I read on here and on the E9 forum that the M90 L-Jetronic intake plenums should be held in place with A-shaped brackets, and these aren't; they're bolted to the valve cover. So that's another strike against it being an M90.
Author of eight books available on Amazon or at www.robsiegel.com

1979 Euro 635CSi
1972 2002tii, 1973 2002
1973 3.0CSi
1972 Bavaria
1999 Z3M Coupe, 1999 Z3
1974 Lotus Europa TCS
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thehackmechanic
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Re: M90 Engine Or Not?

Post by thehackmechanic »

To close this out, I just pulled the valve cover to check how the cam drives the distributor, and what I see is that there's a slotted camshaft adapter nut, part number 11311284801, on the front. This is the OEM part that allows a Motronic head to be back-converted to run with a conventional distributor. I remember this part well, as over 30 years ago I installed one when I put a 533i engine and L-Jetronic injection into my 3.0CSi.

So, since the block has the "3.5" casting, and the head has an "84" year stamp, I think that nails the engine as being an M30B34.

Thanks, everyone, for the help.

--Rob
Author of eight books available on Amazon or at www.robsiegel.com

1979 Euro 635CSi
1972 2002tii, 1973 2002
1973 3.0CSi
1972 Bavaria
1999 Z3M Coupe, 1999 Z3
1974 Lotus Europa TCS
marc79euro645
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Re: M90 Engine Or Not?

Post by marc79euro645 »

Be happy! M90s are notorious for burning head gaskets between the cylinders where they are thinner than the m30b34. Ask me how I know. :)
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jps635
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Re: M90 Engine Or Not?

Post by jps635 »

Be happy! M90s are notorious for burning head gaskets between the cylinders where they are thinner than the m30b34. Ask me how I know. :)
This must be what Jeremy Walton refers to in his book when talking about the development of the M30b34
'85 635csi JPS (RA2-66)
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thehackmechanic
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Re: M90 Engine Or Not?

Post by thehackmechanic »

To close this out FOR REAL, I sent the engine # to BMW archive, and they were kind enough to send me the following:

"Dear Mr Siegel,

Thank you for your email. The engine No. 41993529 belongs to a BMW 635CSi US-version built in October 1984. We hope this is helpful for you. Yours sincerely, Andreas Harz, BMW Group."

So I got it right. It's an M30B34.

--Rob
Author of eight books available on Amazon or at www.robsiegel.com

1979 Euro 635CSi
1972 2002tii, 1973 2002
1973 3.0CSi
1972 Bavaria
1999 Z3M Coupe, 1999 Z3
1974 Lotus Europa TCS
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zinnocoupe
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Re: M90 Engine Or Not?

Post by zinnocoupe »

Interesting post here. I remember when your car was for sale, I was quite interested in it. It looked like it was in very nice shape. Maybe you should post pics and details for the brotherhood here to see and enjoy. Good luck with it all Rob
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jsspagg
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Re: M90 Engine Or Not?

Post by jsspagg »

1980 WBA53310005590352
I see the raised water jacket and what appears to be paint marks to the right of the '3.5"
I cannot seem to find the flat spot above the starter motor to confirm a matching number. Not easily accessible looked on top as well as under the car.
Any ideas why I cant seem to locate a stamped number? Would it appear anywhere else on the motor?

I added a picture, however, it appears that I need board approval for that and am clueless on how to ask.
1980 635 Euro
Under restoration
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Re: M90 Engine Or Not?

Post by jsspagg »

I located the flat spot above the starter. Grease buildup hid the number. With some effort to reach the area and some cleaning in that difficult spot a number was revealed and a borescope used to see it. Good to see those 7 numbers match the others \:D/
1980 635 Euro
Under restoration
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