E32 750iL Engine Swap & Manual Conversion

[sutekh]

I'm hoping this is the start of a lengthy thread documenting the process of swapping / freshening an M70 and ultimately manual converting my 1990 750iL. I started another thread last year about the manual swap portion, but soon thereafter discovered that my candidate car had eaten a valve and ruined the motor which put the project on indefinite hold. It's on hold no longer...

The Car(s)

1. 1990 750iL, 84k miles: I've always longed to own a V12 powered BMW with a manual transmission, and when a straight, low mileage example popped up on a local enthusiast group for nearly free with what seemed to be a blown head gasket, I couldn't resist the temptation to get it running and swap it. The car sat for several months before I had time to tear into it, and I was recently heartbroken to discover that instead of a blown head gasket, it had dropped a valve in cylinder #11 and ruined the left side of the motor. Head is ruined, piston has a hole, Alusil linings on all 6 cylinders on that side are significantly scored after eating metal. Ugh.
   
   The rest of the car is a peach though! Single owner (not counting me of course), straight with no accident history, not a spot of rust, nearly perfect interior. It must be saved!
   .
2. 1989 750iL, 230K miles: Numerous owners, tired suspension, tattered interior, rusty and dinted, operating in limp-mode for undiagnosed reasons, I purchased this car to part out and use anything I needed for ---^ After discovering my 84K motor was ruined, I tested the 230K motor, and the PSIs and leakdown numbers were great. I pulled it apart, and... it looks perfect? Alusil linings are spotless on all 12. Valve train looks great. Okay, I guess I'm swapping motors.

M70 Swap

Even though the M70 in my parts car appears to have good bones, it could certainly use some attention after 230K miles. I'll stop short of a complete rebuild (why mess with the pistons / rings, if there's no wear and everything is sealing well?), but will have the heads rebuilt, am going to freshen the bottom end with new rod bearings, and will replace the chain guides, tensioner, and every seal in the motor. I'll be using the best parts from each motor, and hope to achieve a serviceable, Franken-M70.

Manual Conversion

Finally, the whole reason for this project in the first place! I've already amassed the following, and will be replacing the transmission along-side the motor:

• Getrag 420G (from a '95 540i)
  
• 3-pedal box (from the same ‘95 540i)
  
• M70 to 420G adapter ring (eBay item from Poland)
  
• 850 CSI OEM Flywheel (11221736395)
  
• Spec SB271 850 CSI Clutch / Pressure Plate
  

​Aside from a few incidentals, the only thing missing is a spacer for the flywheel, which I'll either make, or source from the same eBay seller that makes the adapter (previously listed as item #183627857352)

Updates and more pics to follow...

[dannyzabolotny]

I was going to say, TTV makes a flywheel specifically for V12 420g manual swaps, but you've already bought the CSI flywheel.

Ever considered going with an M70/M73 hybrid? You use the M73 block + heads, but with the M70 timing covers, throttle bodies, etc. That gives you 5.4L of displacement, which means more torque and more power, especially with a chip tune.

[sutekh]

I looked at the TTV option, and although lighter, it was a lot more $$$ that even the already ridiculously priced OE CSI part.

The M73 is a great idea, but the fact that I have another M70 in serviceable condition 50 feet away is hard to ignore. Not having a line on an M73 block, I haven't really looked into it, but I assume with higher compression, there's tuning work involved to adjust fueling? I'm anxious to keep the first phase of the project (get it running) simple and within a modest budget. With all the refresh parts and head rebuild x2, it's already going to be well into four figures.

[dannyzabolotny]

Agreed, if you already have the parts and engines ready to go, you might as well build that. In any case, it'll be super cool to see a 6-speed swapped 750il, that's not something we see very often around these parts!

[Zej]

Thanks for posting... I'm following this thread with much interest as I've begun gathering parts for a similar 6-speed conversion on my 1988 750iL.
My ZF4HP24 is on it's last legs and I don't really want to spend the time/effort on repairing it, as at the end of the day it's still a 4 speed automatic.
I'm leaning towards a GS6-53DZ gearbox, as 420g's are rather scarce and expensive over here. Gearing for the 420g would be ideal with the standard 3.15LSD, but the GS6-53DZ will give me a stupidly low 1st gear (up to about 40km/h).
Best of luck with your build and keep us informed!

[sutekh]

Thanks for posting... I'm following this thread with much interest as I've begun gathering parts for a similar 6-speed conversion on my 1988 750iL.
My ZF4HP24 is on it's last legs and I don't really want to spend the time/effort on repairing it, as at the end of the day it's still a 4 speed automatic.
I'm leaning towards a GS6-53DZ gearbox, as 420g's are rather scarce and expensive over here. Gearing for the 420g would be ideal with the standard 3.15LSD, but the GS6-53DZ will give me a stupidly low 1st gear (up to about 40km/h).
Best of luck with your build and keep us informed!

Certainly will do! I hope to have the motor from the donor car out and on a stand this weekend. I'd offer you the 84K mile 4HP24 from the car I'm swapping, but shipping to Melbourne from the US isn't exactly practical :/

[a777fan]

Great stuff. Looking forward to watching.


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[m60power]

Heck yeah this is awesome! I look forward to updates. A v12 stick-shift e32 is as cool as it gets

[sutekh]

No, this project isn't dead! To the great surprise of no one, if you tell the machine shop "no hurry", they'll take over a month to rebuild your heads Looks like they did good work though. I also picked up a spare M70 locally for a couple hundred and am now trying to decide whether to drop it in and run it for the time being while I slowly rebuild the other one, or use parts from all 3 to build the best motor possible...

20191110_150533.jpg20191110_150735.jpg

[DavidQ4]

Great post.

I have an E32 750 and I bought an S6S 560G gearbox from 850 CSI.

I still having some problems with my M70 engine, but maybe if I still having the gearbox when my engine is fine, I will install it.

We dont need to put a different driveshaft?

[sutekh]

Great post.

I have an E32 750 and I bought an S6S 560G gearbox from 850 CSI.

I still having some problems with my M70 engine, but maybe if I still having the gearbox when my engine is fine, I will install it.

We dont need to put a different driveshaft?

Yes, you'll need to modify the driveshaft. If you happen to discover that 560G is just taking up space and you want to unload it, let me know

- - - Updated - - -

Slowly amidst career and family obligations, work on this project continues. Phase 1 (M70 replacement) is well under way. Owing to convenience, condition, and lower mileage, I'll be building the 3rd M70 I picked up. It too had good compression in all 12 and the linings look good now that the heads are off. All that remains before beginning reassembly is removal of the "jesus" bolt (that's sure to be a chore with it on a stand...), harmonic balancer, and lower timing cover, followed by a final round of degreasing. Once done, I'll start the "budget rebuild" (all but the rings and main bearings) with new seals, gaskets, chain, guides, and rod bearings. Should make for a nice winter project

IMG_20191214_112217.jpgIMG_20191217_233358.jpg

On the other side of the garage, the ruined original block has been extricated from the car! Tight quarters made my e39 a bit nervous, but it's 20deg F outside, snowing, and I wasn't about to let my warm air out :P My current plan is to partially mate the rebuilt motor to the 4HP24 (minus torque converter and with only enough bolts to support it) just long enough to swap places with the e28 on the lift. I'm not anxious to remove a rusty exhaust and heavy transmission laying on my back under the car! I've also made the decision to delete the SLS while I'm at this. It's leaking just about everywhere possible, and there will never be a better time to rework the pump / tank and remove the unnecessary lines.

IMG_20191217_232551.jpgIMG_20191217_231318.jpgIMG_20191217_233333.jpg

I encountered one minor setback for the eventual phase II in that my e34 V8 420G's bell-housing will not mate to the M70 adapter ring (starter lobes are in the wrong spot), so I sold that and am on the hunt for an E46 M3 version. Plenty to do in the mean time, however, so not a showstopper. More to come...

[sutekh]

Progress continues. Everything but the block has been through the parts washer and bead blasted. Valve covers and lower pan are off being powder-coated. Ran into a bit of a snag with the rod bearings though. The part number ECS and others cross to as compatible with the M70 isn't--they're too wide--and the OE BMW shells are $30 EACH . I've been discussing options with some of our E31 friends here (https://www.bimmerforums.com/forum/s...-Thread/page11). Anyone here encountered this issue with an M70 / M73?

[sutekh]

The block is a clean as I care to get it and ready for reassembly!

IMG_20200118_223508.jpgIMG_20200118_223523.jpg

But first, I have the above referenced bearing decision to make...

IMG_20200119_115519.jpg

1. Have the motor's original 154k bearings that are broken in to this motor calico-coated, even though they're more worn?
   .
2. Have the less worn but certainly not perfect bearings from the 84k motor calico-coated, even though they're not original to and broken in on this motor?

The mains aren't pictured, but tell a similar tale. Right now I'm leaning toward the lower mileage option, as they've visibly worn through less of the bearing surfaces' coatings.

P.S, here are the two offenders that led to this whole mess. Glad I didn't give in to my initial temptation to re-surface that piston and send it. It definitely has a hole all the way through it!

IMG_20200119_115245.jpgIMG_20200119_115228.jpg

[theBMWbeast]

Wow, that’s some damage! Great progress!

[SergeBMW]

What is the solution for the transmission mount with the 420G? Does one have to be fabricated or is there an easy way with original mounting points? Also can you still utilize the same M70 starter?


I've been wanting to do this for years but hesitant to take on the task while my 750 runs perfect as it is. Trying to source as much info as possible before attempt to do this. Finally a write up of someone doing it so thank you!

[sutekh]

What is the solution for the transmission mount with the 420G? Does one have to be fabricated or is there an easy way with original mounting points? Also can you still utilize the same M70 starter?

The bellhousing for V8 420g transmissions isn't compatible with the M70 or adapter plate. I need one from an e46 M3 instead. I'm going to keep my eye open for a deal locally for the moment, but if I haven't found one by the time the M70 rebuild is complete, I'll buy one and and have it shipped. Looks like the going rate for a used but cleaned and tested example is ~ $1,500.

As far as the rebuild goes, its plodding along. I've done just about everything I can without reinstalling the crank, which has to wait until I receive the treated bearings from Calico. I ended up deciding to send them the best condition bearings from both motors. All 24 bottom rod cap bearings showed almost no wear, so I'm confident this will be a good long-term solution.

[moroza]

Regarding the adapter, what about this?

Regarding the engine, I wouldn't mix and match used bearings. Why'd you decide to forgo a healthy (if higher-mileage) block that needed no rebuilding?

[sutekh]

Regarding the adapter, what about this?

Regarding the engine, I wouldn't mix and match used bearings. Why'd you decide to forgo a healthy (if higher-mileage) block that needed no rebuilding?

That's the exact adapter plate I own (3rd bullet of the BOM on my first post).

The 3rd engine I purchased and am now rebuilding is a "healthy", higher-mileage example that ran well before its chassis was financially totaled, but with 154K it's far from new. I wasn't at all inclined to drop a greasy, worn lump in the car as-is, and if I was going to pull it down to the shortblock for a thorough cleaning, head rebuild, and remove the timing case for a new chain and (updated) guides, etc., then why not finish the job? What I saw when inspecting the upper rod bearings just strengthened my conviction--running well or not, they showed significant signs of wear, even on the 84K block.

What ends up going back in will be all of the lower rod bearings from both motors and the best of the mains from each in very lightly worn and freshly coated condition. I intend to treat it like a fully re-built motor and will subject it to a break-in process.

[JDP530]

What ends up going back in will be all of the lower rod bearings from both motors and the best of the mains from each in very lightly worn and freshly coated condition. I intend to treat it like a fully re-built motor and will subject it to a break-in process.

I would be interested in knowing what bearing clearances you have now after treating the used bearings. You could use plastigage if not a mic to check clearances on rod and crank bearings. I would be tempted to try and use plastigage on both sides of bearings since you are mixing/ matching bearings. Plastigage is not very accurate so micrometer and bore gauge would be much better to use.

Here is a good article on measuring clearances: https://blog.k1technologies.com/how-...ing-clearances

[moroza]

The bullet lists "M70 to 420G adapter ring (eBay item from Poland)" without specifying the L6 or V8 version of the 420G. Later posts suggest you got an L6 version (E46 M3) of the adapter, incompatible with your V8 trans. I've seen people gloss over the difference before and get the wrong adapter plate; just making sure you're aware PMC makes one for the V8 as well.

GS6-53DZ came in two or three L6 boltpatterns. The two I'm sure exist are different from the M5x gassers, one significantly (starter in the wrong place altogether) and the other may or may not work with some hole slotting. The third I'm not sure exists; if so, it would be for early or all M57N1 (not to be confused with the original M57, which had only 5-speeds), and it would work on an S54 adapter plate with one bolt missing, plus the trans clocked 10 degrees and the crossmember and shifter customization that entails. I looked into this for my own swap, and while I only have bits and pieces of this fitment info, it's enough to know that there's more I don't know - a lot of subtleties that most online sources ignore and that'd need to be researched before buying incompatible parts.

[sutekh]

The bullet lists "M70 to 420G adapter ring (eBay item from Poland)" without specifying the L6 or V8 version of the 420G. Later posts suggest you got an L6 version (E46 M3) of the adapter, incompatible with your V8 trans. I've seen people gloss over the difference before and get the wrong adapter plate; just making sure you're aware PMC makes one for the V8 as well.

Thanks for the reminder, but that's definitely not something I glossed over I purchased the "BMW M70 M73 V12 ENGINE ADAPTER PLATE TO M60 420G MANUAL GEARBOX" which absolutely would not work with an M60 420G from a '95 540i. Maybe they sent me the wrong part or made it wrong, but it looks just like all the pics online:

s-l1600.jpg
The gap pictured in red (that's the actual trans I had) doesn't align with the bolt holes on the adapter ring and the starter lobes, relative to where they are on the M70, don't align.

M60_420G.jpg

Unfortunately, I hadn't yet pulled my my M70 when that 420G from a '95 540i popped up locally and I grabbed it. No harm done though. I flipped it for more than I paid Rather than mess with another S6x trans, I was just going to go the L6 route with a replacement ring, but I just got a line on another 420g from a '99 540i locally and am going to check it out tomorrow morning before exchanging anything with PMC.

[sutekh]

I would be interested in knowing what bearing clearances you have now after treating the used bearings. You could use plastigage if not a mic to check clearances on rod and crank bearings. I would be tempted to try and use plastigage on both sides of bearings since you are mixing/ matching bearings. Plastigage is not very accurate so micrometer and bore gauge would be much better to use.

Here is a good article on measuring clearances: https://blog.k1technologies.com/how-...ing-clearances

Thanks. I just received the bearings back from Calico yesterday and they look fantastic. I plan to measure the clearances with plastigage once I get the lower bearings installed and the crank back in this afternoon, and will report back...

IMG_20200208_132636.jpgIMG_20200208_135733.jpg
Attachment 666242Attachment 666241

According to Calico's CT-1 product page (https://www.calicocoatings.com/coati...ilm-lubricant/), the applied film is 0.2 - 0.4 mil thick.

[moroza]

As far as bellhousing boltpattern goes, the only variation among the M6x is starter location for RHD vehicles (EDIT: and I don't think even that changes the pattern; the bellhousing is symmetrical and can accept a starter on either side, only the block doesn't have the big hole drilled on one side). The L6 pattern is way different, so if the adapter mostly bolts up, the conclusion appears to be that it was incorrectly made.

[sutekh]

I've encountered something of a quandary on the bearing tolerance front. I've measured the crank rod and main journals with my mics, and the results are very consistent and repeatable--all within a couple of tenths from their peers: 75.00mm for the mains and 45.00 for the rods +/- .001mm

The bearing measurements, however, are another matter. In the case of both rod and main bearings, I've loaded up several shells of each, torqued down the caps to spec (20NM + 70deg), and measured with my t-gauges. In every case, they're right at the crank journal measurement (i.e., zero clearance) or even a few tenths tighter in some cases. E.g., 74.85mm avg for the mains and right on 45.00mm for the rods.

Now, before you say the Calico Coating thickness is to blame, I see the same thing when I load up a) a pair of the new M30 rod bearings (per above posts, the bearings I bought new that are too wide) and b) a pair of worn, lower bearings original to this motor. All read too tight.

Something must be wrong with my measurement procedure. I'm going to see about tracking down a bore gauge I can rent / borrow. I'm also going to see what Plastigauge has to say on the matter after my Amazon order arrives tomorrow. I suspect I'm introducing inaccuracies with the t-gauges, and initially though the bearing radii might be tighter than those on the t-gauge's feelers, but that's clearly not the case:

IMG_20200209_202120.jpg

Having sets of sacrificial new and used bearings to measure against is definitely helpful. I would not want my freshly coated parts getting scored up like this and have been using 0.004" nylon shims to protect them during measurement, but also wanted to rule out that those weren't introducing the conflicted info I'm seeing.

IMG_20200209_103727.jpg

If there's any good news, it's that the measurements, although too tight, are within a few tenths between the Calico Coated bearings and the worn originals, so I *think* it's going to be alright...

[sutekh]

As far as bellhousing boltpattern goes, the only variation among the M6x is starter location for RHD vehicles. The L6 pattern is way different, so if the adapter mostly bolts up, the conclusion appears to be that it was incorrectly made.

Great info. Many thanks!