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I’m sure most people on here have a ‘bucket list’ of cars to own, but if you’re anything like me, you probably have a bucket list of cars to build as well… This is one of the latter: an old BMW with a silly engine.

This project actually came about when I was left with an S54 (2006 M3 – 340hp) engine after an abandoned project. An on and off search soon yielded a worth recipient of this engine, a 1979 BMW 320/6. Being a 6 pot car, it already has the correct subframe for such a swap, and the M20 mounts can be re-used to mount the new engine. The car was in pretty good shape overall but had been sat for over 10 years and was halfway through being restored when the owner decided to sell. It also came with a whole load of spares (completely filling the car) but most of all it was CHEAP!!

So the deal was done and I made arrangements to pick the thing up. Unfortunately someone reversed into it after I’d viewed the car, writing off the front valance… £50 off and another job added to the list!! anyway, here she is sat at home:









Fast forward almost 18 months and the car looks pretty much the same, but I’m determined to get on with it this year! I’ll try and bring this thread up to date (not that there’s much to see) and then update as I go.

Great, that will be some project, with that engine. Looking forward to it!

Nice exciting plans, looking forward to this build.

time to get cracking

So we’ve seen the car briefly, now let’s take a look at the engine.

Back when I bought this I was planning to do a full rebuild with lightweight pistons and cams etc, nearly 2 years on I think I’ll be throwing it back together to standard spec (340hp will be plenty in an E21). Since I planned to rebuild anyway I bought a cheap complete engine with a rattle – suspected vanos issue. Here it is dragged into the back garden:




I soon set about stripping it down to look for the cause of the rattle







Nowt wrong with the top end, and the vanos pistons were nice and rattle free (I rebuilt them anyway). Keep on digging…






Hmmm that could be it! #4 big end bearing completely shot, along with the crank journal and con rod… I set about ordering the parts required needed but then everything got boxed up so I could move house, which is sort of where this project stalled.

Whow, that can happen with a high rev engine. But with some polishing and custom bearings it wil be ok.

Yes, the S54 is especially prone with its narrow low friction big end bearings, BMW even changed the rod design, bearing clearnace and oil spec early in production due to the number of failures in the field!

I actually bought a good used crank rather than grind this one, but it could be saved with a custom bearing, as you say.

Well, grinding or a polish, I wouldn't grind 1/10 mm off, than a used cranck would be better, but since this is a rather common problem, it will be not to easy to get a replacement. But if a goof pollish will do the trick, than that will be my choice.

Crazy expensive Project - I have also both engines but in 2 cars

I did a complete renewing of the S54 engine last year without a damage on the crankshaft! This will be very expensive - but please don´t stop this awesome Project.

Wasn't there a recall on these bearings? So this one didn't have the upgrade installed, or did it have a long or rough life?

BuschBertl wrote:Crazy expensive Project - I have also both engines but in 2 cars

I did a complete renewing of the S54 engine last year without a damage on the crankshaft! This will be very expensive - but please don´t stop this awesome Project.

Haha don't worry, those pictures were taken nearly 2 years ago, i'm not planing to stop now! I already have (almost) all of the parts to rebuild this engine, but you're right, BMW engines are not cheap to rebuild!

I sourced a good used crankshaft and con rod to replace the damaged items, and i'll balance the pistons and con rods before assembly

And Jeroen, this was a 2006 engine so had the updated bearings and con rods, it must have had a hard life (the 10000 mile service intervals probably didn't help)


More catching up now, this time the gearbox!

Now, obviously the E21 drivetrain won't be able to handle nearly 3x the original power output, so will need to be replaced. There are a few options, the best probably being the ZF 5 speed found in E36 328 tourings, E46 328 and 330s. Its more than strong enough and just about fits in the E21 tunnel. But the more I thought about it, the more I wanted the 6 speed gearbox! The only thing putting me off was the price, then I happened upon an E36 M3 Evo SMG gearbox for just £70!!

The SMG system is a bit strange, in that is uses the same Getrag 6 speed gearbox as the manual cars, but controlled by an ECU. Because the gear linkage is controlled by a computer, the SMG boxes don't have any of the pins and springs that give the gear linkage 'feel' and layout the 'H' pattern that you feel when changing gears. To convert an SMG box to manual, you simply need to add these pins and springs. One way of doing this is to take the SMG bellhousing and machine the holes needed for the pins and add them this way, alternately you find a scrap manual gearbox and swap the bellhousings over! Eventually I found a scrap E46 M3 manual gearbox and set about swapping the bell housing to my good, 60K mile SMG box:



Here is the 2 bell housings side by side, can you spot the difference?


This is a closeup of the SMG, notice the cast lumps? On the manual this is where the shift pins sit


Here is the manual, see the addition of a bearing to the arm, and 2 pins in the casting? this is what gives resistance as you move the gear stick left - right, along with the spring.


Another advantage of the E36 evo gearbox is it uses a 10 spline input shaft which is shared with loads of other BMWs, whereas the E46 uses an 11 spline input shaft and is the only car in BMWs range to do so. This basically means I can use clutch kits and flywheels for M50/52/54/S50 cars, which tend to be cheaper than E46 parts.

E36 10 spline:


E46 11 spline:


Sorry for all the words and boring pictures, but i love all this nerdy technical stuff

I promise the next update will be more interesting!!

Me too!!! Keep it comming!!! Lots more, I want lots more!!! Love it!

Respect, btw.

Good and creative thinking! You make the conversion to manual sound so easy haha

Moving on, obviously the old M20 has to go and I also want to clean up the engine bay somewhat. That will mean moving the fusebox inside the car (and probably replacing it with a blade fuse box), battery will end up in the boot and removing that eyesore of a brake servo!






Also since I plan on mounting the new engine at the same angle as the M20, I made a mockup 'engine' by mounting the S54 head to the M20 block. Off with the M20 head first!




Then the S54 head placed on top. The head bolt spacing is actually the same length-ways, but the S54's head bolts are wider apart. Still, i could get 2 head bolts in which is enough to keep it there. I also used some head bolts and cardboard to space the head up, as the S54 block is 10 or 12mm taller than the M20



With the 'engine' in, i could start looking at exhaust manifold routing, space for the airbox, radiator mounting etc.

Amazingly, the rear S54 manifold is a perfect fit! The front will work too but needs to be chopped after the collector. This is good because A) the primaries are all equal length and tuned for the engine, and B) I don't have to faff around making exhaust manifolds





I'll probably change the flanges, and might need to modify the routing of the rear mnaifold, we shall see.
Here you can see the front manifold clashed with the steering coupler, but I'll cut it where it snakes close to the block and all should be good



Then over to the intake side - THOSE THROTTLE BODIES!!!



The airbox technically fits, but not much chance of getting an elbow onto the inlet. I'm sure i'll think of something for that... currently thinking of a hard pipe with a flange that bolts to the airbox? or a fibreglass cowl maybe? any thoughts are welcome!




I also threw the vanos on to check for rad clearnace - as expected i'll need to recess the radiator into the front panel (later 6 cyl cars came like this from factory)



and finally a parting shot with the cam cover on:



Looking good already

Cool!!! Rad in front of the bumper than?