M90 questions

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mopar
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M90 questions

Post by mopar »

Hi,

I pulled my m90 (1980 euro Motronic 1.0) motor out of the car, for a soft rebuild (new gaskets, timing chain, ....) and I got some questions about it:
- are the valves good for unleaded fuel and LPI or do they have to be replaced?
- are the torque specs the same as for the m30 motor (head, covers, sump,...)
- I got the torque specs for an m30 head but what about all other torque specs for the motor, where can I find this info? I got the repair manual for the 1979 e24 but there is no info about the torque specs....

After rebuild this car is going to be the daily driver for my wife, so I want it to be problem free after the work is done.

Hope to find some answers here.
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86_6series
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Re: M90 questions

Post by 86_6series »

Here are specs but I don't see M90 engine.

Still, you may be able to get some info. 2 sources same PDF

http://www.mwrench.com/Whitepapers/torqspec.pdf

https://whatismycar.com/files/bmw_bolt_ ... ations.pdf
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mopar
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Re: M90 questions

Post by mopar »

Thanks for the list, will look into for the m30 engine.
Mine is m90 (m30 head on m88 block), hope the specs are the same.

Someone any info regarding the valves and fuel?
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Re: M90 questions

Post by bpoliakoff »

IIRC the last year of the M90 was model year 1981. An 88 block should not be an M90
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
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mopar
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Re: M90 questions

Post by mopar »

My discription was not correct, it is a 1980 M90 motor, matching numbers with the car.

But still no answers to the case....
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zinnocoupe
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Re: M90 questions

Post by zinnocoupe »

Good questions here.

As far as I know the valves are ok with unleaded. I've never seen anything posted that says otherwise. ive seen a few people who have rebuilt M90s and there was no mention of special valves. LPI? Propane?? No idea on that

I used the same torque number etc when I did my m90 head. and any other torque specs I just used the bentley. I didn't touch the bottom end so can't comment on that. The head gasket is M90 specific and cost more too.

I just googled "BMW M90 torque specs " and got some pretty good info, with a bit more digging you'll find the answers I think. Good luck

So I got to ask.... if your wifes daily driver is going to be an m90 powered car, whats yours?? :D
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Pasocb
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Re: M90 questions

Post by Pasocb »

Hi Mopar,

My apologies for chiming in late on this. As others have alluded to, you can utilize the M30 engine specifications to rebuild a M90. Basically, the engines only differ in basic bore/stroke geometry, piston crown design and cam profile.

Your question regarding our engines' suitability to run unladed fuel is a good one and has some mixed controversy due to the transition period when the cars were produced. Given the heads are constructed from aluminum with high quality steel/iron valve seat inserts, these engines are inherently better suited to running unleaded fuels. Some say that it is no problem at all, others stay that BMW changed the metallurgy of the inserts around 1985 to better run the unleaded fuel that had been prolific for quite some time by then.

When rebuilding my 1981 M90, the valve seats had almost no wear. The head is original to the car with over 100,000 miles on it. This is all empirical evidence on my end, so take it for what it is worth. We lightly touched up the seats and valves with the grinding stones prior to reassembly.

cb
1981 635 Hennarot
1980 635 Polaris (Project)
bpoliakoff
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Re: M90 questions

Post by bpoliakoff »

^++1
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.
mopar
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Re: M90 questions

Post by mopar »

Thanks for the answers regarding the valves and torque specs.

Now I am making a variant on the iron maiden tool so I can take the camshaft out and test the valves on air tightness.
Than I can take the valves out and the head can be flattened for reinstall.

When the tool is ready I will post a photo of it, it costs about € 15,00 on material and a half day work to make it, hope it works fine.
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Re: M90 questions

Post by Drew »

Be interested to see piccies of your iron maiden tool please. I tried to DIY build one also, but it was a hopeless failure! And I ended up stripping and rebuilding the head without the benefit of the tool.
+1 on what others have said, I've run an M90 on unleaded with no adverse. I currently run an E9 on unleaded and the compression is just fine, no sign of valve seat damage.

Re torque specs, I use two Haynes manuals, one for E3 and one for E12. Usually they agree. On head bolts they don't agree however, and it looks like head bolt specs for M30 engines have 'evolved' over the years.

You'll probably already know this, but don't use a M30 head gasket on a M90. M90 gasket is harder to source, but is the only option.
mopar
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Re: M90 questions

Post by mopar »

The dutch version of the iron maiden, I found this on a site of a dutch fellow but the dimensions he mentioned where wrong, I corrected them and made this in half a day, the total cost is € 27,00 including all the bolds (also the eight M12 bolds to fix it to the head).

Image

Here you can tighten the valve springs on the inlet side first and then the outlet ones so they don't hit and bend.
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Re: M90 questions

Post by Drew »

Nice work, it's a simple design that, steel bar and angle iron, some drilling and tapping looks about it. No welding?

Is there any protection for the rockers? They're softer than the steel bolts and will be gouged (or worse) as the bolts are tightened
mopar
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Re: M90 questions

Post by mopar »

I have to make connectors so they push on the excentrics and not on the rockers, will post pictures when they are ready.
Got the materials and made them to fit, only here I got to weld.
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Re: M90 questions

Post by Pasocb »

In my opinion, this version of the tool is one of the more elegant. It has an advantage that it is adjustable for any cam profile. I did noticed that the dimensions and angles given on-line seemed a little off. Presumably something got lost in my translation?

So far I have not found a need to fabricate a tool like this. I have always been completely disassembling the head not just removing the cam. To do so, I remove one end of one of the two piece rocker shafts by loosing the rockers, removing the rocker/shaft clips and shifting the rockers off the cam lobes as needed to completely release all valve spring tension. Initially, the cam is rotated to an ideal position to help facilitate this. I do not recall if it is best to start with the exhaust or intake shaft. A quick study of the cam lobes will tell.

I suspect having a tool like this would be a time saver and could prove useful.

cb
1981 635 Hennarot
1980 635 Polaris (Project)
mopar
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Re: M90 questions

Post by mopar »

This is the connector for the rockers:
Image

The M10 bold fits in the connector:
Image

And the connector fits on the rocker arm excentric:
Image
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Re: M90 questions

Post by Lieuwegaal »

Good topic! =D>

As I pulled my M90 and took it apart, I am looking into the possiblity to rebuild it myself or get it rebuild (with improvements where possible).
Loving the answers and will follow this topic untill and after I decide what to do with the engine.

Cheers!
mopar
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Re: M90 questions

Post by mopar »

In the head of mij M90 are 2 pipes sticking out to guide de head on the block, can I just pull them out to clean the surface of the head?

With pliers?

They have to be removed when the head will be flattend, so I want to do it now then I got a flat surface to lay the head on.
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Re: M90 questions

Post by Pasocb »

mopar wrote: Wed Jan 20, 2021 10:34 am In the head of mij M90 are 2 pipes sticking out to guide de head on the block, can I just pull them out to clean the surface of the head?

With pliers?

They have to be removed when the head will be flattend, so I want to do it now then I got a flat surface to lay the head on.
One can insert the shank of a drill bit (or any other steel rod) that is a tight fit into the center of the hollow dowel. This prevents collapsing the dowel when gripping with a small pair of vise grips. IIRC, several supply houses sell replacement dowels in cases of loss or excess damage.
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mopar
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Re: M90 questions

Post by mopar »

Thanks for the fast reply, will try it with an insert and a vise grip.
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Re: M90 questions

Post by mopar »

Got them out now the next thing to do is clean the block surface

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Re: M90 questions

Post by bpoliakoff »

Hard to see in the picture but what are the stampings on the top of the piston?
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.
mopar
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Re: M90 questions

Post by mopar »

Here you can see it better, I think the engine had a rebuild in the past but I am not sure

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Re: M90 questions

Post by bpoliakoff »

M90 bore size is 93.4 so that very well should answer a question Usually when boring and replacing pistons the piston should/could have the oversize from stock stamped on the piston showing the oversize the it was bored to using factory specs and if it was bored oversize the stamping should either show the bore size in relation to the original as either the amount over stock or as a plus first oversize
Last edited by bpoliakoff on Thu Jan 21, 2021 9:40 pm, edited 2 times in total.
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.
Drew
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Re: M90 questions

Post by Drew »

When I did mine, the block was true, but the head needed a skim. I don't recall anything standing proud from the head, and I was able to leave the alignment parts in the block in situ. Lowering the rebuilt head has to be done gently and accurately to avoid those alignment parts scoring the newly machined head!
IIRC the rearmost head bolts need to be loosely in the head when refitting as the scuttle / firewall gets in the way once the head is in place

Nice work on the iron maiden!

After a skim, has anyone worried too much about timing? I.e. fitting an adjustable cam sprocket?
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Re: M90 questions

Post by bpoliakoff »

I was concerned when my motor was rebuilt as even if they skimmed the head the block was also surfaced so I bought an adjustable timing gear just to be safe. It was years ago, but I think I paid around $100
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.
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