M90 questions

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Pasocb
Posts: 86
Joined: Wed Aug 09, 2017 11:14 am
Location: Paso Robles CA

Re: M90 questions

Post by Pasocb »

mopar wrote: Wed Jan 20, 2021 5:36 pm Got them out now the next thing to do is clean the block surface

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Prior to reassembly, completely clear all the head bolt holes of any residual oil or debris. I like to confirm that a head bolt will easily thread all the way in by hand to each hole when I am done. It is common on these engines to suffer cracked blocks and failed head gaskets due to folks over looking this step.

As you mention, clean the block surface to remove all residual gasket material and corrosion with a sharp scraper making sure to not score the surface at any of the sealing areas. It is good to check the block for flatness with a good straight edge, but I have yet to find a warped block needing milling. I like to finish up with a good scrub down using brake-clean or something similar to remove all oil or grease just prior to placing the gasket.
1981 635 Hennarot
1980 635 Polaris (Project)
Pasocb
Posts: 86
Joined: Wed Aug 09, 2017 11:14 am
Location: Paso Robles CA

Re: M90 questions

Post by Pasocb »

Drew wrote: Thu Jan 21, 2021 6:59 pm 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?
IIRC, BMW specified the head thickness at 129mm and allowed up to 0.5mm of material removed before the cam timing dropped out of spec.
My thought is that if the total machine work on the head and block combined is less than 0.5mm (0.019"), we should be in spec. Of course this is all assuming that the block has not been previously decked.

It would be interesting to obtain the cam specifications for the "7" cam that M90s were equipped with. This information would be useful to those with heavily milled heads.
1981 635 Hennarot
1980 635 Polaris (Project)
mopar
Posts: 53
Joined: Tue Sep 29, 2015 8:45 am
Location: Belgium

Re: M90 questions

Post by mopar »

The Iron Maiden has been tested and after some fine tuning it dit the job, so the cam is out (good advise RT(F)M more than once) ](*,)
Rockers are out so I can test the valves.
mopar
Posts: 53
Joined: Tue Sep 29, 2015 8:45 am
Location: Belgium

Re: M90 questions

Post by mopar »

Are M30 valves the same as M90 valves?

I had a leak in cilinder 1, the inlet valve die not close, I thought it was some dirt from the disasembly, but after cleaning the valves intake nr 1 is not closing, it remains open about 5mm without springs. The valve is bent.
I lapped all the other valves with succes.
So I need to replace one intake valve for my M90
mopar
Posts: 53
Joined: Tue Sep 29, 2015 8:45 am
Location: Belgium

Re: M90 questions

Post by mopar »

My intake valve is:
Valve stem 7,95mm
Valve diameter 45,85mm
Total lenght 107mm

Does anyone knows what the dimentions are for an M30 intake valve?
Pasocb
Posts: 86
Joined: Wed Aug 09, 2017 11:14 am
Location: Paso Robles CA

Re: M90 questions

Post by Pasocb »

mopar wrote: Sat Feb 06, 2021 8:04 am My intake valve is:
Valve stem 7,95mm
Valve diameter 45,85mm
Total lenght 107mm

Does anyone knows what the dimentions are for an M30 intake valve?
M30 and M90 valves are the same with exception to later b35 heads that have 1mm larger intake valve heads.

I believe the specified valve stem diameters for M30s is 8mm and the valve head diameters are 46mm.

You should be able to safely source parts using any E12 base car as a look up reference.
1981 635 Hennarot
1980 635 Polaris (Project)
mopar
Posts: 53
Joined: Tue Sep 29, 2015 8:45 am
Location: Belgium

Re: M90 questions

Post by mopar »

Thanks for the info, now I can order an M30 valve with the diameter of 46mm, I saw M30 valves at € 5,00 a piece on bmwclassicparts.nl, thas no money.
mopar
Posts: 53
Joined: Tue Sep 29, 2015 8:45 am
Location: Belgium

Re: M90 questions

Post by mopar »

Valve problem solved, got a M30 valve and replaced the bent valve, fits like a charm. :D
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