M90 or m30b35 or both?

[ledge67]

Hi all, it's been a long time since I have been lurking on here and need some advice for my e9.

A few years ago I purchased a m90, long water jacket and verified when the head was removed for rebuild. Sadly when cleaning the parts, I had found the valves had just touched the tops of each piston. I did not want to risk bent valves and an already milled head ruining my rebuild, I mothballed the project.

Speed ahead 4 years, I now have an opportunity to get a complete m30b35 from a mates e34 for cheap. I need the head to continue building my m90. This will be a carb car as i have a set of new 45 dcoes ready to go. Having a m30 and a m90 gives me options.

M90 with m90 head with b35 valves

M90 with b35 crank, 2mm milled off pistons

M30b35

Input would be appreciated.

 

[sfdon]

Location?

 

[rsporsche]

he would be in OZ ... Adelaide

 

[sfdon]

I think it may last 5 seconds.....
A “k” or “7” cam in a m90 head with
big ? (+1mm) B35 valves could impact a m90 piston very nicely. Maybe you should clay it. There is no relief on the intake side of a m90 piston. If you cut the pistons 2mm (.0787) how does that compare to the intake relief of the stock m30b35 piston? Keep in mind it will expand 20 thousandths when it gets warm.Btw- why not just buy 6 b35 valves? 100 bucks buys the valves new.

 

[ledge67]

Yes Adelaide in oz. The m30b35 crank is what I'm leaning towards, no replacement for displacement. The piston damage was most likely caused by over rev from the previous owner before he crashed the 635CSI. The m90 has flat top pistons and a 84mm stroke and the b35 has a 86mm stroke. By cutting 2mm off the pistons, it should return the piston protrusion back to m90 spec. Using the m90 cam in the b35 head should result in a standard m90 head with +1mm diameter valves and larger porting. I was lead to believe that the newer valves were only a larger diameter, but were standard length.

I looked at new valves, but it put me down the upgrade path. New valves, springs, valve stems, adjustable cam gear and a newer head with better coolant galleries.

 

[sfdon]

M30b35 head on m90 block is a no go unless you buy custom pistons.
Bigger combustion chamber drops compression to 8:1 from 9.3:1
Steals 20+ hp.
Go with double valve springs from W&N- really good price.
They are stock From m30b35
High lift cams are a disaster on flat top pistons.
Crank is a good idea- I’m doing the same right now.
My machine shop guys don’t much care for the bigger valve. Lots of work not much action.
There are two m90 heads- early and late. Completely different intake ports.
Later is better.

 

[ledge67]

I've had a quick look at the prices of valves, springs and retainers, its alot of money. I am thinking of stripping apart the b35 head and installing the valves and springs into my m90 head, thus repairing the head, i already have the thicker m90 head gasket to keep compression the same with the faced m90 head. Mill 2mm off the m90 pistons and install the b35 86mm crank. So it would be something like:

M90 head- b35 valves, springs, valve stems/seals- m90 camshaft
M90 -2mm pistons milled
M90 rods
B35 crankshaft

I will need to look at my head to determine the port shaping, i think it is the earlier type with the large lug at the top of the port.

 

[sfdon]

Measure your head .... what’s the thickness?
You may not need that special gasket.
You will need to check valve guides.

 

[ledge67]

I can't remember what the exact thickness of the head, but it had already been faced and the head gasket I have is the correct size for it. The m90 is supposed a special head gasket, due to some coolant ports in the block, but I can't understand why, if it runs the m30 head.

I will order new valve guides and stem seals.

 

[sfdon]

M90 has 2 coolant holes between bores
Must run m90 gasket
M90 head or any head you use must have twin coolant holes or you will have a dead end steam hole

 

[sfdon]

M90 has 2 coolant holes between bores
Must run m90 gasket
M90 head or any head you use must have twin coolant holes or you will have a dead end steam hole

 

[Gazz]

Listen to the Don - he is THE MAN.

His advice will save you $$$, time and angst.

Angst def: see German car. Sub': restoration.

 

[sfdon]

Correct block pic of m90 - first pic was actually a 10:1 with a smudge looking like a coolant hole. Posted from cell phone!
2014? Someone local did the m90 block, 86 mm crank, machined piston, b35 head combo. From memory it worked fine.
Searching for contact info for you.
You can imagine what happens if you don’t drill the head to match the block.
Obviously a second gen m90 without the water jacket.
We see a lot of valve strikes on these.

 

[ledge67]

Does the later cams have a higher lift to cause the valve strikes? I don't think the head would last long without those passages.

 

[sfdon]

Does the later cams have a higher lift to cause the valve strikes? I don't think the head would last long without those passages.

I believe all m90 heads had “7” cams.
Be very careful with any other cam.
Must clay to verify.
It’s not the head that’s the problem with coolant holes - it’s the block. You have a hole with air in it.... not good for heat transfer.

 

[ledge67]

It seems the best option is to rebuild the m90 head with the b35 valves, b35 springs and m90 cam. This would mean changing to the later style valve guides and stems. I have looked at the ones from IE which seem reasonably priced, but how can I tell if I need the oversized guides before I take it to the machine shop?

 

[ledge67]

Is there anything else worth sealing off the e34? I'm thinking of taking all the accessory brackets and components. Alt, starter, PS pump etc. The e9 power steering squealing is very annoying.

 

[Markos]

Ac compressor?

 

[sfdon]

Machine shop will tell you if you need guides.