Engine rebuild advice [BMW M50 engine]

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Positive thoughts : I had good results many years ago when I gave 2 dead engines to a machine shop, and asked them to pick the best bits - fix anything else - to get me 1 decent engine. The place is a local 1-man engineering place, not sure a bigger outfit would be interested.
Strip what you can yourself so it's easier for them / cheaper for you (I removed and kept the heads so the shop only had to fix the crank/bottom end )

Negative thoughts : it sounds like a great idea but look at the prices of spares before you make a descision. BMW parts aren't cheap, some bits are dealer only £££. Add lots of labor £££ and you might be cheaper getting a good used engine or a complete car (MOT-failure?) as a donor.

Cheers for the replies guys

nomad Aye I would look to split the engine if its easier for them, could just get them to build the bottom end and I could fit the head at home or something. Parts cost wise, I'd be using used 3.0 parts, can usually get the bits for around £300 or so, so it would be the cost of labour on top of that and consumables like bearings, seals etc.

welshpug In theory yes, but in practice there are a lot of hurdles to overcome with putting the M54 in an E34. Since I already have an M50, it would be easier to keep this and stroke it, mainly because of management and wiring simplicities.

I was originally thinking of DIY'ing it, but read a couple of articles online about plastigauge perhaps not being so accurate? Which has made me re-think

wont the m50 map be totally unsuitable for a 50% increase in capacity?!

much cheaper to make a loom and ecu from the m54 work than building a whole engine.

just a note I have a complete m54b30 sitting on a pallet beside me (in Belfast) I removed it from my e39 530i sport due to head gasket failure, was quicker and easier for me to buy a complete running engine and throw it back in, I recall the head gasket kit alone was a couple of hundred quid hope this helps

Cheers guys

skkylinedave the parts are pretty readily available as 'stoker kits', its a fairly common mod to do to M50's, an alternative is to use the same rotating assembly from an M52b28 to make a 2.8 stroker. so I'm not too concerned about finding the right parts, the bit about crank regrinding is good though, something to take into consideration, new rings and bearings I would be assuming anyway so I'm not too bothered about the cost of those.

welshpug 20% increase in capacity by my maths? going from a 2.5 to a 3.0? (I'm selling/throwing away the 2.0 engine currently sat in my 5)

ChasR Both please trust me when I say the M50 stroker is the preferred route to trying to put an M54 in an E34 Its a mod that has been done before so I'm not going off the beaten track here. Issues with an M54 would be trying to make all the OBD2 level sensors etc. work with the OBD1 E34 body loom, also M54 is aluminium block, which while not an issue in itself, does limit future mods in comparison to the M50 iron block.

nomad Aye I've done a bit of costing work so far on parts and they're not too bad in my opinion for the M5x-era stuff. The machining costs is something I would try to get a ballpark figure on when I find a suitable place to do the work


Overall I'm set on doing the stroker mod, so while putting an M54 in is 'a way' of doing things, its not what I want to do. The point of the thread was more to understand exactly what would be involved so I'm armed with a bit more knowledge when it comes to talking to an engine rebuilders.

So far I'm thinking the following:

Hone of the bores ahead of fitting the replacement pistons
New piston rings, gaps checked
Measurement of big end bearing caps and buying new bearings to suit?
Measurement of crank, polishing/regrinding if required?


I could just go into a machine shop and say 'whats it gonna take to mate these parts' but thought it would be good to go in armed with some info.

Also wanted to get recommendations for places as I've had issues with garages/bodyshops/wheel refurbers doing curse word work before and I really don't want to be dealing with a place that mess up my engine!

Cost wise, I'm not trying to do this on the super cheap, I appreciate it will cost a bit of money (within reason) but I will have a freshly rebuilt engine as a result, which to me isn't such a bad investment

does the OBD2 thing just mean a single 4 pin sensor for engine and dashboard rather than the separate pair of two pins for the older vehicles?

still 20% difference in capacity is enough for the maps to be wrong, it may well run but nowhere near ideal.

I'd have thought an alloy block was a plus point, stiffer and lighter?

I think Adam is referring to them overheating.

Certainly with the M52 it suffered from a few issues including:

-Sulphur killing the bores ; this admittedly is now a historical issue and oddly Nikasil is meant to be harder than cast iron in terms of a surface for that application.
-Blocks becoming brittle after sustained overheating, meaning you are banking on helicoils/timeserts of keeping the head on the block correctly, assuming the block's not too brittle. Not an idea scenario for a brand known for not having the best cooling systems.
-I'm guessing there are tuning benefits too like going Turbo etc. The M50 bottom end is known for being tough.

I *think* he could get lucky on the maps. I think BMW may have made an M50B30 but for other markets like Japan. I know a racer was on about "slipping" in a 3.0 into an E36. With that being the case he could always acquire the ECU as well.

I think my Porsche specialist used to use someone in Coventry.

If you wish you can contact him, but he is grumpy and not always helpful! Kevin/Ben or Alex Eacock at EMC Motorsport will know where to go. I know Ben and can ask him if you wish.

AFAIK they are the only outfit to have a 968 finish the Britcar 24Hour, so they know what they are doing .

Get the engine shop to measure up the journals and buy the appropriate bearings or regrind oversize etc.Id always get a crank polish when swapping the bearings even for std size.