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+--- Thread: BMW M51 Questions (/showthread.php?tid=6860)
BMW M51 Questions - silverzx - 11-03-2015
Hi all, I have recently acquired a M21 mechanical inline pump.
Are these a straight swap with a M51 electronic inline pump? Obviously when converting I'd need a 3 series accelerator pedal and cable, is anything else required?
![[Image: IMG_7019.jpg]](http://s29.postimg.org/x83epz3kz/IMG_7019.jpg)
Next, I want to try run this pump (which will have a 12mm head) with my 12cm HX35. Is this just being over ambitious or is it likely to spool it?
![[Image: 12029101_1163339573681503_42192877_n.jpg]](http://s23.postimg.org/kpfigou0n/12029101_1163339573681503_42192877_n.jpg)
Other plans are 3" exhaust, boost controller, large aftermarket FMIC, boost gauge, EGT gauge, external wastegate possibly, maybe water meth.
Lastly, I assume that for over 250 bhp I will need ARP head studs, does anyone know if any other BMW engines have the same size/thread/length head studs? ARP don't stock any directly for the M51.
RE: BMW M51 Questions - whitey1986 - 03-05-2016
What engine model/year do you have? If it is the earlier engine with alloy inlet manifold then you will need to make a spacer for the boss on the mechanical pump as it's like 2" dia whereas the later engine block has a 3.5" dia hole
RE: BMW M51 Questions - whitey1986 - 03-05-2016
Sizes may not be exact but that's what you're looking for roughly
RE: BMW M51 Questions - silverzx - 06-14-2017
(03-05-2016, 01:16 PM)whitey1986 What engine model/year do you have? If it is the earlier engine with alloy inlet manifold then you will need to make a spacer for the boss on the mechanical pump as it's like 2" dia whereas the later engine block has a 3.5" dia hole
Well after some headache I figured this out for myself, upon pump removal I managed to snap one of the lugs (FFS it was so close to completion)!
Now I'm kinda set back a lot as I need another pump or need to repair this one. Would welding it likely damage internals?
Also, where would you get a spacer or what would you use to make a spacer to fit over the end of the pump?
Picture to show size difference of either pumps end, the mechanical one obviously needs a spacer and currently causing major oil leak:
![[Image: IMG_6791.jpg]](https://s29.postimg.org/ulk8mkupf/IMG_6791.jpg)
![[Image: IMG_6792.jpg]](https://s29.postimg.org/3p09e9bw3/IMG_6792.jpg)
Picture to show the snapped part of pump in question about welding:
![[Image: IMG_6782.jpg]](https://s29.postimg.org/sshby99ir/IMG_6782.jpg)
Any help much appreciated to try finish this off.
RE: BMW M51 Questions - silverzx - 06-20-2017
BUMP.
RE: BMW M51 Questions - starynovy - 07-01-2017
Could be welded of only stripped to parts.. seals will burn. Spracer is simple ring turned on lather with notch for O ring to seal against block.