Exploring potential - M42->M52 Swap

[dc318icabrio]

Hello,

I am still in the early stages of even thinking about this so would like opinions. I have a 91 318i convertible that I am slowly fixing up. The engine is in good shape, I just did the upper and lower oil pan gaskets, the mess under the intake mod, suspension is refreshed, it starts right up, no funny noises. It has 185k miles and runs rather well. I will repaint it soon, and it's a great car so far. I recently came across a complete 98 328i 5sp that I can pick up for very cheap. It's a cosmetic mess but the mechanicals are very solid. I am considering just buying it, parting out the stuff I don't need(body panels, interior, seats, etc) and then potentially swapping the motor (and whatever else) into the 318ic. I would then sell the m42 as a complete motor. The donor car(328i) is cheap enough(around $1k) and is a complete car. I've been reading up on the swap and now have a general idea of what to expect. The question is, is it worth undertaking? The car right now is very fun(albeit slow) and needs very little else apart from a repaint. I know the m52 transforms it. I do like that I can get the complete car, so I'll most likely keep it obd2. Also seeing I can use my existing trans? I feel like once I part it out, i will come out ahead and if i sell the m42, it will be even better. Would you do it? I like the simplicity of the way it is now but that 6cyl power is tempting. Would love to hear your thoughts.

[mtech325]

If you don't mind the 318 for what it is, I'd say keep the m42 especially if it runs fine and has been reliable.

The 24v swap on a 318 has a few extra steps than an e30 325 because you'll want to replace the differential and transmission. The m42's g240 and small case differential are just not cut out for the larger engines. People use them, but you do run the risk of blowing them up and having to replace them, so may as well do it correctly the first time around.

The good news is that the 328 with a manual transmission will have most of the parts you need. The M52 comes with a zf320 like an M3 would, and it'll have the correct 4-bolt driveshaft. You will however need a diff in the range of 2.93-3.46 if you want to be able to drive on the freeway at a reasonable RPM. You will need the front sump oil pan setup out of an e34 525 still, and may need to modify the dip stick to work with the OBD2 CCV depending how you go about it.

Another thing to consider is that you'll want to do as much preventative maintenance on the 24v swap as you can while the engine is out, so figure 1500-3000 bucks to refresh things like the cooling system (namely ditch M42 radiator setup), clutch/flywheel, custom exhaust, and all the little pieces that'll nickel and dime you.

At the end of the day though, it's your car and you'll have to go the route that's best for you. The M42 in my 318is blew up and went the 24V route. The extra power/torque is nice for a street car, and the m/s5x engines are pretty easy to live maintain and have the bonus of serpentine belts. The Bring A Trailer purists will probably say the M42 is the "baby M3" engine and that it should be left in the car, but it's also an expensive engine to repair when things go wrong. A friend of mine has a low mileage cherry example of a 318is, and his engine blew up. He's about $4500 into rebuilding it to stock specs and it's still not in the car. Granted it'll be a new engine, not used, but nearly the same money will get you a modern motor with 50+ horsepower & torque that can still get great MPG...(my S52 car got 29mpg on a 400 mile trip @ 80 mph). If push comes to shove...24v every time ;D

[dc318icabrio]

Thanks, that's very useful info. Out of curiosity, what in the m42 blew up? Rod bearings? Chain tensioners? I know its a solid and expensive engine but i foresee parts for it becoming rare eventually simply because there arent that many of them compared to a 6cyl. I guess the idea of a modern 24v i6 in an e30 is so tempting. Thanks again for all the info.

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[Mwishlist]

My post won't be nearly as informative, but I went down a similar route with a 325i convertible. I swapped an S52 into it and it's a complete blast. However, whatever you think your budget needs to be; double it if you want to do it right. There are so many little things you need that add up and then there are the "nice to do while I'm in there" like a better steering rack, etc.

[mtech325]

Thanks, that's very useful info. Out of curiosity, what in the m42 blew up? Rod bearings? Chain tensioners? I know its a solid and expensive engine but i foresee parts for it becoming rare eventually simply because there arent that many of them compared to a 6cyl. I guess the idea of a modern 24v i6 in an e30 is so tempting. Thanks again for all the info.

Sent from my ONEPLUS A5000 using Tapatalk

The m42 in my car trashed itself at 141k due to a failed chain guide which caused the motor to jump timing (so much for the m44 updated tensioner). My friend's car had/has roughly 70k original miles when it spun a rod bearing. This was unfortunate as the motor had a lot of preventative maintenance from a previous owner and it was a very tidy example. In fairness though, my dad had an e36 318is with an m42 that another friend currently owns with ~150k, and that engine has been fairly trouble free, so it'll vary from car to car.

As you've pointed out, parts are becoming a little tougher to source simply due to age. The 24v 6-cylinders on the other hand are plentiful since they were available the e36, e34, and e39, so it's easy to get parts new or used from a junkyard.

Mwishlist brings up a good point. With the engine out, it's the perfect time to do the e36, z3, and/or e46 steering rack swap (they're all very similar), which genuinely transforms the driving experience on any e30.

[Codym42]

I just finished up an m52 swap into my 318is. I've only driven it a few times but it is so much more entertaining to drive. $1000 for the donor car is a good deal and will save you a lot of hassle down the road. I found myself going on several trips to the junkyard to get little parts that I didn't know I needed. As said above, the best thing to do is use the ZF transmission and buy another diff.

I have over $7000 into my swap but I replaced pretty much all of the wear items (clutch, cooling system, hoses, new 944 booster) and did an e36 steering rack. I also paid more for my engine because it was aluminum block. Don't forget about the cost of a custom exhaust as well.

This is the list of parts I used: https://www.r3vlimited.com/board/sho...2&postcount=27

PM me if you have any questions about the swap. I'd love to help!

[dc318icabrio]

Thank you for the info. How long did the swap take you? Also, who did the ECU reflash to remove rear o2/secondary air, etc? The parts list is very helpful. What I like is that the donor car is complete and runs and so will be easier than trying to find stuff in the junkyard.

I just finished up an m52 swap into my 318is. I've only driven it a few times but it is so much more entertaining to drive. $1000 for the donor car is a good deal and will save you a lot of hassle down the road. I found myself going on several trips to the junkyard to get little parts that I didn't know I needed. As said above, the best thing to do is use the ZF transmission and buy another diff.

I have over $7000 into my swap but I replaced pretty much all of the wear items (clutch, cooling system, hoses, new 944 booster) and did a z3 steering rack. I also paid more for my engine because it was aluminum block. Don't forget about the cost of a custom exhaust as well.

This is the list of parts I used: https://www.r3vlimited.com/board/sho...2&postcount=27

PM me if you have any questions about the swap. I'd love to help!

[Codym42]

After I had all of the parts, it only took about a month. I pulled it apart after Thanksgiving and had it running before Christmas.