M47 Crankshaft

[BMWApex]

So I've been looking for an m47 crankshaft for a stroker build. Are all m47 crankshafts usable in an m42? Or are there specific ones that I should be looking for? Thanks for any advice!

[DesktopDave]

I've never done this, so I'll wait for others to chime in, but there are differences. I believe the late model M47N(?) cranks won't work. It seemed to me that these were primarily the M47 motors installed in Range Rovers. They had a shorter snout due to a relocated oil pump.

[bmwman91]

There are two versions of the M47 crankshaft as far as I am aware: one from the Range Rover and one that was used in BMW. It is my understanding that both need some machining to work in the M42 block, but the Range Rover one needs a lot more work and an adapter piece made in order for it to be compatible with the front main seal, chain sprocket and damper hub.

[Warsteiner]

Did someone say stroker  ...... I went directly to my BMW dealer and ordered a crank for an E46 320d. Had my machine shop turn down the nose to fit the crank sprocket and add a keyway. I also figured while you're there to just lighten the crank a little bit. Not sure what the going price is these days but that's what needs to be done. You could go the M47N route but you'll need that adapter for the nose. I believe Metric Mechanic can make you one. Then you can weigh out your options as to which one fits your wallet better. Good Luck!! Plenty of info on strokers and I have one piece of advice for anyone doing it.......do your math and then do it again to be sure. And maybe a 2nd one too.... Go with at least 11:1 compression and get some good cams.

Cheers,
~Ralph

[bmwman91]

RealOEM shows the difference between the M47 and M47N crankshafts fairly well. It is pretty obvious why the M47 one is an easier retrofit.

M47: https://www.realoem.com/bmw/enUS/showparts?id=AL71-EUR-10-2000-E46-BMW-320d&diagId=11_2227

M47N: https://www.realoem.com/bmw/enUS/showparts?id=AS71-EUR-02-2002-E46-BMW-320d&diagId=11_3314

For reference, the M47 crank that MM built my engine with cost $1250 new, and it took them 3 months to get it from Europe. This was in 2012.

There appear to be a couple of them available on eBay in Europe. They are all used, and a lot cheaper, but it is a real dice roll since you cannot know for sure what condition it will be in. If the bearing journals need refinishing, you may or may not be able to make up for it with oversized bearings. If you search "M47 crankshaft" on eBay there are a number of hits, although most are the M47N.

[XCELIR8]

Did someone say stroker  ...... I went directly to my BMW dealer and ordered a crank for an E46 320d. Had my machine shop turn down the nose to fit the crank sprocket and add a keyway. I also figured while you're there to just lighten the crank a little bit. Not sure what the going price is these days but that's what needs to be done. You could go the M47N route but you'll need that adapter for the nose. I believe Metric Mechanic can make you one. Then you can weigh out your options as to which one fits your wallet better. Good Luck!! Plenty of info on strokers and I have one piece of advice for anyone doing it.......do your math and then do it again to be sure. And maybe a 2nd one too.... Go with at least 11:1 compression and get some good cams.

Cheers,
~Ralph

Hi There I have M47 crank I want to throw into my M42 aswell.
Now Im just curious to know how much I need to machine off the nose of the crank?
And seeing that im going to be using the m42 rods if I use the std m42 pistons what would the apparent CC be by just changing the crank?

[Warsteiner]

You need to "turn down" the nose on the crank until the gear fits back on.

I can tell you that you won't be using the standard M42 rods and pistons with a M47 crank.

You need to do the math to figure out how it will work.

Cheers,
~Ralph

[XCELIR8]

Ok Thanx I have some time so think ill figure it out closer to the time when Im ready to do the swap
Im still actually enjoying the M42 as is in the e30 a refreshing upgrade from the m40.

Im most likely leaning towards using the 86mm pistons from the Opel if I cant source the s50 pistons

[Warsteiner]

Now you're on the right track!!  You'll also need to add another keyway (woodruff key) since the one on the M47 crank is not in the proper position.

Cheers,
~Ralph