Refurbishing an M90 and converting from L-Jet to M1.3

[FlyingBrick]

Greetings! A couple of years ago I bought a grey market euro 1980 635csi locally because I wanted the transmission and engine. After quite some time I finally started digging into it, that I might eventually stick it in here:

The goal is to convert it to Motronic 1.3, so that electronically it's more or less a drop in to my '89 E30 325i, as typical M30B35 swaps are. Currently I have the the block on a stand, head is on my workbench. Timing covers and chain are off as well as all ancillary components. I've spoken to a couple of knowledgeable guys, as well as read every thread I could find from here, mye28, bigcoupe, and anywhere else that came up in my googling. I know roughly what I need to convert it, but have some extra questions and I'm sure more will come up as I endeavor to refresh it. I know I need the upper timing cover, I know that keeping the log will be extra work, I need to fab some sort of throttle bracket system, fab a way to secure the new fuel rail, etc.

I hope to use this thread as a place to document some of my build, and tap the many resources I will need along the way. In my research I found this site and along with bigcoupe (I'll be cross posting on here and bigcoupe so don't be surprised if you're also on there and see the same or similar questions) you guys seem like the experts on M90s, which most of the guys on the E30 boards haven't even heard of.

First question is: it looks like I need to change the camshaft to run the M1.3 distributor? My M90 was from a 1980 635csi, with the stick-up, gear driven distributor. I see no provision for the shaft and pin used on the Motronic distributor rotors. From my reading I was led to believe that the M90 and M30 cams had the same profiles in terms of degree/lift/whatever. Someone on bigcoupe kindly informed that this is not the case. I want to maintain the character of the M90 so I'd like to keep the same specs as the current cam in the head. This made me think of the M1.1 M90s, which have the distributor rotor and cap that I'm used to seeing on my M20. Can I source a camshaft and upper timing cover from one of these? Will it be the same as the one I have now except for being able to support the mounting for the distributor rotor?

At this point I do plan to re-use the log manifold. I've read that the 320i runners are often swapped for better performance. Again, a fellow on bigcoupe said he had heard of minimal gains to be had on an M90. Are 320i runners worth obtaining to use in place of the original M90 log runners?

Thanks for any help! I look forward to speaking with you guys for the foreseeable future as I slowly refurbish this legendary power plant and get it back on the road.

[Mike W.]

There is a lot of mystery about the early 3.5 AKA M90 engine. The cam is the biggest one. As much as I've read and seen, I really don't know the answer. I will say this, if you want to stick with a stock BMW motronic cam, use the B35 one, although some say it's the same 264 as early motronic 3.3s, an acquaintance who measured a number of cams says it's much more similar to a Schrick. As far as using E21 320i runners on the older manifold, it improves torque as they're longer, but not HP. And with a lot of engine in a smaller lightweight body I for one wouldn't bother. Of course it's extremely difficult at best if not impossible to change a cam in an assembled head, you will probably need to pull the head to swap the cam. But out of the car it may be possible, though not easy. If you do pull the head to swap the cam, be aware you need the early 3.5 HG, the bore is 93.4, not 92 like the later cars.

I reread your post and an underlined question was about the upper timing cover where a motronic dist cap bolts onto. Yes, they are the same, from 82 on. The adapter on the end of the cam determines a bolt on or push on rotor and cap, along with a specific spark plug cable set, but the casting that bolts onto the head is the same.

[FlyingBrick]

Thanks for the reply Mike. Here is what a well established member on bigcoupe had to offer regarding the cam: "the M30B35 cam is a slightly longer duration/higher lift cam than the one fitted to a euro M90 motor...The cam will lose you a little torque low down but you will get a bit more higher up." I'm used to driving my M20B25, which in typical BMW I6 fashion requires you to keep the revs up to get HP and TQ from it. I'd like to keep the M90 as much like an M90 as possible, so less low end torque in exchange for higher end torque doesn't interest me (if his information is correct). I'll already be gaining significant HP and TQ just by swapping engines so I'd rather have the lower end torque that M90s are known for.

As I mentioned, my M90 is already disassembled, so I have the head off and will need to replace the head gasket anyway. This also means I have much more possibility of changing cams. I will need to change the cam no matter what as it had the slotted end meant to drive the L-Jet distributor, and I foolishly was rotating the entire assembly out of curiosity using the handle of a 17mm combination wrench which fit perfectly into said slot...until one of the sides of the slot broke off. I immediately realized I should have been using a crescent wrench to turn the giant (38mm+?) nut on the end of the camshaft, but regardless I will not be able to use the current camshaft at all, so a swap to something is required at this point. If my research is correct, the "late" M90s (late being a relative term for an M90) were M1.1, but still M90s, no? This would mean that their camshafts were equipped to drive a Motronic distributor rotor, but should be identical in lift and duration to the "early" M90s, like mine? Hence if I could source one of these M1.1 M90 cams I would have the same lift and duration as mine, but with the provision to drive a M1.1 (and as such, a M1.3) distributor rotor?

Forgive me if I'm not grasping what you explained, but what do you mean by the upper timing cover determining whether a bolt on push on rotor and cap can be used? I was under the impression that the cam determined the type of distribution to be used, and that the upper timing cover was simply a byproduct of the cam type? For instance the cam currently installed is (was) slotted, meaning it could only drive the old style L-Jet distributor, and that if I switched to a Motronic cam, that could drive the later style distribution system, it would simply necessitate I use the later timing cover, with the large circular area for the later Motronic distribution rotor to spin in? Basically, the timing cover is just that: a cover, and the cam is what determines the type of distribution and as such, the cover you use.

Thank you for the info about the E21 320i runners. If I can easily source a set within the budget and time constraints of my build (aka a very long time before this will be seeing the E30) I will try to pick some up, otherwise I won't worry. I'll also make sure to obtain the proper head gasket when the time comes to purchase one.

[Mike W.]

As I mentioned, my M90 is already disassembled, so I have the head off and will need to replace the head gasket anyway. This also means I have much more possibility of changing cams. I will need to change the cam no matter what as it had the slotted end meant to drive the L-Jet distributor, and I foolishly was rotating the entire assembly out of curiosity using the handle of a 17mm combination wrench which fit perfectly into said slot...until one of the sides of the slot broke off. I immediately realized I should have been using a crescent wrench to turn the giant (38mm+?) nut on the end of the camshaft, but regardless I will not be able to use the current camshaft at all, so a swap to something is required at this point. If my research is correct, the "late" M90s (late being a relative term for an M90) were M1.1, but still M90s, no? This would mean that their camshafts were equipped to drive a Motronic distributor rotor, but should be identical in lift and duration to the "early" M90s, like mine? Hence if I could source one of these M1.1 M90 cams I would have the same lift and duration as mine, but with the provision to drive a M1.1 (and as such, a M1.3) distributor rotor?

It looks like you want to go motronic anyway, but if you wanted to retain a conventional distributor there is a repair nut just for what happened to your cam.

I don't know what makes a M90 a M90, some feel it is a specific block, others regard it as a bore/stroke/compression combo with or without a distributor or motronic. And they are all rated the same. Anyway, I'd say the cam may be the same between early motronic (1.0, btw) and L-jet. Or not, measured specs are hard to come by. To complicate it even more, some US spec 82-84 5/6/733 cars came with heads with an M90 marking instead of M30. However that means nothing that I can tell, although there are those who claim they have a 264 cam as opposed to a 260 in late 84 and B34 3.5s.

Forgive me if I'm not grasping what you explained, but what do you mean by the upper timing cover determining whether a bolt on push on rotor and cap can be used? I was under the impression that the cam determined the type of distribution to be used, and that the upper timing cover was simply a byproduct of the cam type? For instance the cam currently installed is (was) slotted, meaning it could only drive the old style L-Jet distributor, and that if I switched to a Motronic cam, that could drive the later style distribution system, it would simply necessitate I use the later timing cover, with the large circular area for the later Motronic distribution rotor to spin in? Basically, the timing cover is just that: a cover, and the cam is what determines the type of distribution and as such, the cover you use.

I think you misunderstood me, the later timing covers are all the same once they went motronic and eliminated the distributor. However the ends of motronic cams aren't all the same, the early ones are set up for a push on rotor adapter, which takes a push on type cap and specific wires. There is a conversion adapter which may still be available for the early motronic cam which allows you to use a bolt on rotor etc. Later cams, starting in the US in 1-84 all use bolt on components. The reason I make something of a big deal is cap, rotor and spark plug cables run around $200 so you don't want to get the wrong ones.

Trivia. Earliest motronic is 1.0. With US cars, E28 535's went to 1.0a (adaptive) 1.1 started in 87 with 528es and in 88 on 6/735s with 1.3 coming in a couple of years later. 1.1 to 1.3 saw few differences, it might just be the ECU.

[FlyingBrick]

Thank you Mike, that's some helpful and useful information. Do you happen to have a part number or place to look for the adapter you mentioned?

In the event it's not available, I can use a 1/84+ cam that will natively accept the bolt on rotor adapter, I just won't be able to to be certain it will be the same degree as my current L-Jet cam?

[wkohler]

I'd run the B35 cam and I'd also run the B35 intake manifold, too. You'll have to port-match the head, but I think it will be more at home in the E30 than the L-jet manifold.

The very last M90s in the '81 production 635s were Motronic and ran the 002 ECU. They used the 3.2/3.5 intake like the M30B32 and M30B34, used the aux air valve and idle control valve together, etc. No difference in the motor from the '80 production cars. They did run the push-on rotor like the Motronic *33 cars did. The push-on stuff is more-expensive than the bolt-on. That said, the B35 cam is the ticket and you're guaranteed to use all the late stuff. I think an M90 will run very well on Motronic 1.3 as it's static compression ratio and other characteristics are very similar to the M30B35, though it was rated with more power than the M30B35. You'll gain better drivability and with that, I'm sure more power, which is absolutely necessary in a car that has the weight of a running shoe.

Also, when you get the motronic timing cover, be sure to have it machined to match your head. Figured you probably knew that, but it's worth mentioning.

[Eric Q]

Do you have to deal with smogging the car? It would be interesting to find out if an M90 with Motronic 1.3 will pass a smog test. In general M90s have a reputation of being dirtier than even a Euro M30b34.

If it runs relatively clean, I would love to run Motronic 1.3 with an M90. Those engines are so smooooooth...

[FlyingBrick]

I'd run the B35 cam and I'd also run the B35 intake manifold, too. You'll have to port-match the head, but I think it will be more at home in the E30 than the L-jet manifold.

The very last M90s in the '81 production 635s were Motronic and ran the 002 ECU. They used the 3.2/3.5 intake like the M30B32 and M30B34, used the aux air valve and idle control valve together, etc. No difference in the motor from the '80 production cars. They did run the push-on rotor like the Motronic *33 cars did. The push-on stuff is more-expensive than the bolt-on. That said, the B35 cam is the ticket and you're guaranteed to use all the late stuff. I think an M90 will run very well on Motronic 1.3 as it's static compression ratio and other characteristics are very similar to the M30B35, though it was rated with more power than the M30B35. You'll gain better drivability and with that, I'm sure more power, which is absolutely necessary in a car that has the weight of a running shoe.

Also, when you get the motronic timing cover, be sure to have it machined to match your head. Figured you probably knew that, but it's worth mentioning.

Outstanding, great reply. So a B35 cam from a late car with the bolt-on stuff is what I'm looking for now. Someone on bigcoupe mentioned needing a cam sensor if I went this route?

I'm not sure which manifold I'm going to go with yet, I'm trying to keep this relatively low-cost and wanted to avoid the pitfall of getting machine work done. I may still investigate the costs though.

What about the upper timing case needs to be machined? I think that's the second time I recall hearing something about that. Why wouldn't it just bolt right up properly?

[FlyingBrick]

Do you have to deal with smogging the car? It would be interesting to find out if an M90 with Motronic 1.3 will pass a smog test. In general M90s have a reputation of being dirtier than even a Euro M30b34.

If it runs relatively clean, I would love to run Motronic 1.3 with an M90. Those engines are so smooooooth...

I live in CT and my E30 qualifies as a classic (20+ yrs, used to be 25) so I believe I'm exempt from emissions testing. I could be wrong though. Either way I plan on running a straight exhaust, possibly with a resonator in the middle. I have to do more research on M30 sounds vs M20 sounds, which is what I'm familiar with. This is far down on my list of priorities at the moment.

On the same topic however, are the euro M90 exhaust manifolds known to flow better than average, alright, or shitty? I plan to use those on the engine until I can afford the OEM euro bundle of snakes headers.

[Mike W.]

You need to machine the upper timing cover if the head has been machined, they should be the same thickness. Exhaust manifolds. From Realoem it looks like they're just Bavaria manifolds which differ from later US spec B32/B34 manifolds mostly by a slight rotation and change of angle on the output flange, not by any significant difference in port or discharge size. The later B35 exhaust manifolds do flow better, are larger and would be an upgrade if the engine is exhaust restricted. Euro bundle of snakes? Never heard of it. I have the only M30 bundle of snakes headers I've seen.





I agree with Chris on the B35 cam, I think I mentioned it earlier. I disagree with him on a B35 intake, without a B35 head I don't see the advantage, the most significant difference I've seen is the port shape which matches the B35 head port shape. But not earlier ones. And if you have the head off, don't even think of reusing it without replacing the valve guide seals. If it hasn't already been done, or if it was done a long time ago, they will literally be crispy hard and no longer a seal. I've broken many of them just breaking the head down, before I even got to try to remove them.

[FlyingBrick]

Thanks for more great info. I had believed the head was never machined, but I remembered a receipt in the folder of records I got from the previous owner (who in turn received it from the original owner) for some headwork done. Here's what the receipt says:

-Diag misfire cyl 2/3 no compression
-Remove head replace valves and rocker arm eccentrics because of excessive wear + bad gasket
-Replace spark plugs

Under accessories on the bottom of the receipt, however, it says

-Resurface exhaust $30
-Clean + machine head $60

What sort of machining would $60 get you? Certainly not the head being shortened, no? And would replacing the valves mean the valve guide seals were also done? This was done at 43,000 miles according to the receipt, and the engine had 105,000 when I pulled it. Is this long enough that I should replace the valve guide seals again?

I had part #'s 11-62-1-307-250 and 11-62-1-307-251 as the M88 M635csi snake headers, I must have connected the blocks being the same and not considered the heads being completely different. D'oh.

[Mike W.]

Many shops won't replace a blown head gasket without surfacing the head, even I won't. I suspect that's what the $60, clean and machine head charge would be. Measure it, from the factory they come either 5.079" or 5.083". At least 60K and perhaps as much as 100K on what may be original valve guide seals? Especially since you're going to have the cam out, I'd do them. They may not need it, but you're 3/4 of the way there and seals are cheap. It's Murphy's law, if you do them they will have been done with modern ones that are nice and soft, but if you don't do them they will be original and cause you to burn oil.

[wkohler]

M90s have those old valve guide seals, so I'd do them if it were my moter.

[FlyingBrick]

Thanks for the help guys. The head service was done in 2001 or 2002 I believe, but does not specifically mention the seals. I will replace these regardless since I have the time and access. Can I pull the part # from realoem for the M90 specifically or should I be looking for later M30 ones?

As for the measurements of either 5.079 or 5.083, is this measured from the flat valve cover surface down to the bottom of the head?

Aside: Any idea on the rough cost of having a shop fully clean my block (exterior is in nasty shape) and o-ring it? Cost of cleaning the head/valve job/replace the cam/replace the valve seals?

[Mike W.]

Thanks for the help guys. The head service was done in 2001 or 2002 I believe, but does not specifically mention the seals. I will replace these regardless since I have the time and access. Can I pull the part # from realoem for the M90 specifically or should I be looking for later M30 ones?

Just use M30 ones, a M90 is really just a specific M30. If work was done that recently, it would have good ones if they were replaced, but since you don't know...

As for the measurements of either 5.079 or 5.083, is this measured from the flat valve cover surface down to the bottom of the head?

Correct.

Aside: Any idea on the rough cost of having a shop fully clean my block (exterior is in nasty shape) and o-ring it? Cost of cleaning the head/valve job/replace the cam/replace the valve seals?

Careful, I see mission creep. A shop can't do much more with an assembled short block than you can. Unless you're planning to take it apart completely and have it hot tanked. O ringing the block is unnecessary unless you're going to turbo it, and even then it's a luxury. As far as the head, location and the individual shop makes a difference, and I strongly suggest you look for the best place in town, not the cheapest, there's still a lot of good 'ol boys who only want to work on cast iron and will only begrudgingly work on ferign stuff. I would guess $3-400 to break down, valve job (which would include installing your seals) and reassemble. In case that seems expensive, and it used to to me, it's not. There is a lot of time involved in breaking the head down and reassembling without breaking anything. Oh, they're going to want to sell you valve guides too. They will be worn, but unless they're really, really worn, don't generally cause a problem. But that'll be another hundred bucks.