M50 build options

[E30godz]

I'm interested in doing a little rebuild of a 1993 M50 with 260k miles on it. It runs very strong so i wont do this for a bit but i wanted some opinions/thoughts...I would like to just do a basic rebuild + S50/S52 crank and maybe M3 cams. What pistons/rods would i have to use in order to do that succesfully?

Thanks!

[FredK]

If I were you, I would leave well enough alone for the time being. You'd be opening up a huge can of worms.

260K is probably around the time you'd need to go to a +1 overbore on the cylinders because they can no longer just be honed. Also, the valvetrain is now fairly aged, and just doing the bottom end would be a recipe for disaster. It's not just a matter of slapping in the right crank and rods. There are a lot of ancillary components that you should or need to replace during a bottom end refresh.

Your valvetrain will be taxed with the higher lift M3 cams, and by now with 260K the lifters probably are decently noisy and will not go the distance. The head could kick the bucket after another 50K.

My suggestion is to find an S50 engine with lower miles and install it in the place of your M50. The project won't take nearly as much time, and won't have any cost and time overruns associated with taking stuff to the machine shop.

If the S50 is out of your price range, I'd look at sourcing an M52 and installing M3 cams into it. That combo can produce a lot of power, and is fairly cost effective.

My two cents, anyway.

[Ball325]

or he could just do the necessary updates to the m50.....it doesnt cost nearly as much as your making it sound. if he can source the parts and get them and then have the valve train upgraded. S50s are expensive as hell minimum 2.5k and if ti ahs 100k on it then its worth freshening while it out which is another $500-$1000

[FredK]

Yes, if you do it right, it will cost a lot. Almost as much as an S50. He doesn't need a wiring harness or ECU, so he can save $300 right there, should he try to find a used S50. S50s are getting cheaper now.

New main and rod bearings $120
New rod bolts (required) $40
New main bolts $10
New head bolts $15
New gasket set, block and head $175
New timing rails $70
New lower timing chain tensioner $80
New upper timing chain tensioner $50
New main timing chain $35
New upper timing chain $20
New oil pump chain $20
New 84mm rings $90

Used S50 valve springs and retainers and (10/95+) collets $100
Used rods $200
Used S50 crank $300
Used S50 cams $250

Machine shop work
Recondition / mic valves $50
Hone $70
Valve job $250 (includes deck, valve job, new valve guides)
Shave M50/52 pistons $100

That's already $2045. This ASSUMES you can shave the pistons to get the proper CR and the valves don't have worn stems. It also assumes the 260k mile oil pump would be reused. This would be a rather risky proposition. You'd also need some kind of software tuning. I've also assumed he'd be using the cheaper of the two (s50 or s52) cranks.

The resulting engine would be virtually new, though. You couldn't guarantee the used S50 would be in as good shape as your newly rebuilt stroker engine.

[aeryk7]

I have heard of people just putting an s50 head on a m50 block

[FredK]

Yeah, that can be done, but it'd be essentially the same as installing S50 cams into an M50TU. That is certainly one way to go. Turner sells software for S50 cams in a M50TU, and you do see pretty noticeable gains.

The only difference would be the absence of conical valve springs and retainers.

[E30godz]

Are there any rebuild kits out there that include basic rebuild parts for an M50 (sans head, of course)? I searched for a bit and came up nil.

[Addissimo]

Fred, you're right on here.

I started to do an engine rebuild and was appauled at the cost of everything. I ended up selling all of my parts like an s52 crankshaft rods pistons etc.

Getting a kit wont really help you. You're going to need to see what exactly is needed after the engine is torn down.

With that many miles, you're probably going to have to machine the main and rod journals on the crankshaft, so you'll need oversized bearings. While you're at it, you might as well knife edge the crankshaft. The rods may need to be replaced. You'll probably need to overbore the block, so you're looking at $550+ for pistons.

Everything Fred said + a new vanos motor at $320.

Low mileage m52 + s52 cams/head & custom software. It's the way to go.

[The Fast One!]

Yes, if you do it right, it will cost a lot. Almost as much as an S50. He doesn't need a wiring harness or ECU, so he can save $300 right there, should he try to find a used S50. S50s are getting cheaper now.

New main and rod bearings $120
New rod bolts (required) $40
New main bolts $10
New head bolts $15
New gasket set, block and head $175
New timing rails $70
New lower timing chain tensioner $80
New upper timing chain tensioner $50
New main timing chain $35
New upper timing chain $20
New oil pump chain $20
New 84mm rings $90

Used S50 valve springs and retainers and (10/95+) collets $100
Used rods $200
Used S50 crank $300
Used S50 cams $250

Machine shop work
Recondition / mic valves $50
Hone $70
Valve job $250 (includes deck, valve job, new valve guides)
Shave M50/52 pistons $100

That's already $2045. This ASSUMES you can shave the pistons to get the proper CR and the valves don't have worn stems. It also assumes the 260k mile oil pump would be reused. This would be a rather risky proposition. You'd also need some kind of software tuning. I've also assumed he'd be using the cheaper of the two (s50 or s52) cranks.

The resulting engine would be virtually new, though. You couldn't guarantee the used S50 would be in as good shape as your newly rebuilt stroker engine.

your essentially right, but he would have to uses50 crank since the s52 one is VERY hard to install properly.

pistons would be stock m50 pistons.
that set-up gives you a 2.9 stroker with 11.5 CR

you need to run 93 octane AND custom software,

AA makes the software for 800 dollars.

[Brew]

The 2.9L setup requires machined stock or custom pistons.

I started to go that route- had almost all of the parts to do it - and decided to scrap the whole thing and go with a low mileage S50. Its about upgradeability-- with a custom 2.9L you are stuck with AA's setup unless you get custom tuning, which is $$$. If you want to S/C or turbo down the road, you're basically screwed because nobody makes software for the non-vanos.

Stock, low mileage S50 is the way to go. Get a 3.5" HFM and 24# injectors w/ Conforti software while your at it and you'll have plenty of power (unless you're a freak like me) and factory-like driveability.

[Ferret]

I'm not really familiar with the costs over there in the U.S., but maybe you should consider putting in a used low milage M50 of M52 instead of going into the hassle and expanse of rebuilding your old engine.