Author Topic: M47 crankshaft to M42 (Read 10713 times)

paulmiko · « **on:** September 20, 2012, 03:24:56 PM »

Hey guys, I'm new to this forum, hope you'll accept me to your team, and help me navigate through discussions! Here's the deal: I have an E36/5 Compact with an M42B18, now the engine (along with the front suspension) was a total bust (head gasket blown, poor piston rings, dire need to change seals, differential, clutch etc.) so I decided to perform a major repair and also add some modifications if possible. So aside from the typical intake/exhaust mods, I have read a few topics about the crank change (m47) and a one-mass flywheel from an M20 installation. I live in Lithuania/Europe, so it's not to hard to find the M47 crank, but my main question is: what pistons (or a combination of piston heads and rods from different engines) should i use, to increase the displacement to at least 2.0l? And will the M20 flywheel just bolt-on fit with the standard M42 clutch? Please don't offer me to "simply swap an m50" because I really like the M42 (also the A/C that came with it

) and I'm just wondering whether it could be improved. Also, it's almost impossible to find the S50/S52 pistons here so you can also scratch those off the advice list

. Thank you for your time, I hope I posted in the right topic section.

bmwman91 · « **Reply #1 on:** September 20, 2012, 05:04:18 PM »

I don't have all of the details about these things, but I do believe that you need an M47 crank specifically from a Land Rover since the front of the crank / snout is similar enough to be adapter to the M42. You will still need to grind a new keyway into it and I think that it also needs to be shortened. Hopefully some of the more knowledgeable members can post too!

EDIT:
Sounds like the Land Rover crank is the one that you DO NOT want.

DesktopDave · « **Reply #2 on:** September 20, 2012, 06:25:04 PM »

Welcome to the 'club! Nice to meet someone from Lithuania - two of my great-grandparents emigrated from Vilneus way back in the 19th century to raise their families here...that makes me 1/4 Lithuaninan!

Anyhow, I wish I knew more about a stroker engine like this - never having built one myself I'm sure my advice would be poor. I've been researching the clutch though - here's a few tips I've picked up (someone please correct me if I'm wrong here):

The M40/M42/M43 use a smaller diameter flywheel than the M20 did (215mm vs. 228mm), so you'd need the matching clutch kit along with the single-mass flywheel. You'd also need a later model M20 flywheel as the tooth pitch on the starter ring changed after mid-'88 IIRC. The M20 flywheel also needs a bit of machining to clear the main seal housing bolts on the M42 motor. The release bearing is the wrong size too, some have suggested the e21 323i part as a perfect fit. Check this thread out for five long pages of clutch details...

Alternatively, you can use the M40 single-mass even though it's slightly smaller in size. Those apparently fit perfectly but cannot take as much abuse. Make sure you check all your parts out on RealOEM.com or BMWFans.info - a little time there can save you a lot of frustration and likely a good bit of money!

paulmiko · « **Reply #3 on:** September 21, 2012, 03:21:03 AM »

Thank you for the replies! That's actually very interesting to hear DesktopDave! It's always fun to find someone related to Lithuania or someone who atleast knows there is such a country

So I understood that the M47 crank still needs some work done to install, that's ok and thank you for the info! Also, I got my hands on an M44 block (with internals) and head. Would it be possible to swap an M44 head on an M42 block? What modifications need to be done and are there any gains? I've also read, that people use M44 rods with shaved (2.5mm) M44 pistonheads, to gain an approx 1996cc displacement, could that be true?

Geoff · « **Reply #4 on:** September 21, 2012, 08:40:40 AM »

it is possible to install an m44 head on a m42 motor. thats the way mine is set up. there are a few things to fiddle with, but it is mostly a strait swap. The biggest catch was there is one temp sensor on the m44, and 2 on the m42 head. Not trusting myself to get it right, I used a machine shop to drill and tap the hole for the 2nd sensor.
Is it better than before? I dont think so..maybe a tad smoother of an idle, but when we did the head it got all new hoses and all that crap under the intake(throttle body heater) was taken out, so maybe its smoother because its all sealed up with no vacuum leaks. The swap worked tho, so if you feel like tinkering you can-but it will not be a nite and day difference.
Geoff

DesktopDave · « **Reply #5 on:** September 21, 2012, 12:53:59 PM »

Again, I have no firsthand experience...but I figured that the M44 head was inferior to the M42 part...mainly due to its use of finger followers instead of the cam acting directly on bucket tappets. Now that I think about it, if the revs are kept low it'd make no difference and might improve efficiency just by causing less drag.

OTOH, the valve stems are thinner, right?

On a more personal note - I finally read up on a little Lithuanian history. I'm amazed at the breadth of it. The Grand Dukes, the Tetonic Knights, the Kingdom of Rus. Amazing stuff. We get none of that here, unfortunately. 'merican history is all about 'merica, and it's all politically filtered to the point that it's virtually worthless.

strypt · « **Reply #6 on:** October 11, 2012, 07:17:47 AM »

I have built a 2L M42 with the M47 crank from a 320d. From what I've seen on a pic of the Rover M47 crank the nose is much shorter and requires a adapter to be able to use it. Thus the crank from a BMW is preffered. That one requires a second woodruff key in the nose of the crank and the nose is a couple of 1/10 mm larger. So either make the nose smaller in a lathe or make the cam sprocket + adapter for the vibration damper larger.

Then you must of course find a suitable combination of pistons and rods if not custom ordered.

JXD · « **Reply #7 on:** January 28, 2020, 12:37:28 PM »

Quote from: strypt on October 11, 2012, 07:17:47 AM

I have built a 2L M42 with the M47 crank from a 320d. From what I've seen on a pic of the Rover M47 crank the nose is much shorter and requires a adapter to be able to use it. Thus the crank from a BMW is preffered. That one requires a second woodruff key in the nose of the crank and the nose is a couple of 1/10 mm larger. So either make the nose smaller in a lathe or make the cam sprocket + adapter for the vibration damper larger.

Then you must of course find a suitable combination of pistons and rods if not custom ordered.

I can't find pics of a modified Rover crank

Somebody can help me ?