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Old 12-06-2016, 01:52 PM   #1
jaredmac11
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Figuring out Options for E30/E36 M42 build

I am rebuilding an e36 M42 and planned to swap it in to my E21.

I got the head off and took it to a machine shop to run some tests and they verified there is a crack on one of the exhaust seats... No bueno. They have an M42 head for $300 that I could consider.

I also have an E30 M42 in my garage. It sorta fell on my lap mid-build and I couldnt say no to the price. I was just planning to hold on to it for later.

I have all the parts I need for a rebuild for the E36, minus hoses. I have none of the parts needed for a rebuild for the E30 (not including any parts that may overlap), which is what is giving me pause.


The draw to the E36 M42 were the knock sensors, the improved intake manifold, the stonger timing case, and a few other pieces. I think the E36 M42 also gave a few extra HP. But all that doesnt mean much when I have a shot head.

What options do I have here? Could I, for example, take the E30 M42 block and head and plug in the e36 timing case? could I take the E30 head and drop it on the e36 block? I have some time on my hands and I can start trying to see what works, just curious if anyone has already run through this.

Ive done a lot of searching and there are a lot of inconsistencies.. but I also understand this isnt too common of a scenario in the first place.
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Old 12-06-2016, 07:04 PM   #2
e30sh
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Check the build date of your e36 M42...top of block above starter dd/mm/year format. Only the 94 / 95 ones had the improved timing case. 93-95 had the 6mm valve stems. 92 is 7mm and dual valve springs like the e30 version. Everything interchanges. The early cams having a little more duration according to Delta Cams.

Good luck.
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Old 12-06-2016, 07:18 PM   #3
jaredmac11
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Quote:
Originally Posted by e30sh View Post
Check the build date of your e36 M42...top of block above starter dd/mm/year format. Only the 94 / 95 ones had the improved timing case. 93-95 had the 6mm valve stems. 92 is 7mm and dual valve springs like the e30 version. Everything interchanges. The early cams having a little more duration according to Delta Cams.

Good luck.

Very helpful! Mine is a 95, definitely has the improved timing case since it doesnt have that sprocket. Its a rail instead.
I didnt know the e30 was 7mm and I definitely didnt see dual springs in this e30 head til you mentioned it and I had a second look. Thats news to me.


Also learned my e36 engine was built 27/04/95. Also didnt see that before.

Thank you very much. I'd like to maintain the e36 timing case and I guess I'll be using the e30 camshaft, valves, etc.. Was the e36 spring configuration and 6MM valve guide clearance an improvement in performance? or is the difference negligible? I wonder what each set up gave you...

They are all hydraulic lifters right? So I can use whichever is least worn, I'd assume
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Old 12-07-2016, 02:17 AM   #4
fresh_TD
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You why to use the 6mm valves, they are lighter.
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Old 12-07-2016, 05:21 AM   #5
jaredmac11
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I guess its a mostly useless thought-- it would be too expensive to swap out the valve guides and use the springs, valves, etc. RealOEM seems to show that the Camshafts are completely different part numbers as well, so at this point it would make most sense to just use the E30 head completely.

It's a shame my e36 M42 head is cracked, but if I cant use the good e36 head, all the components go out with it I suppose. Unless I'm mistaken.

I can at least get a quote from a machine shop and see if it makes sense but it feels like the cost:benefit isnt worth it.
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Old 12-07-2016, 06:10 PM   #6
e30sh
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U may gain a touch of compression with the 7mm head. BMW never changed the advertised compression ratio of 10:1 but did take some dish out of the 93 up (6mm stem head) piston according to the Mahle site. To get back to 10:1, the head chamber would need to be bigger.
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Old 12-09-2016, 11:54 PM   #7
TobyB
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Quote:
just use the E30 head completely.
You should be ok doing it that way. I don't think you'll notice any real difference...

t
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