Avoid swap to high mileage m42?

[jaredmac11]

I am looking at a 91 318i with an odo that stopped rolling at 200k. PO says it stopped before he bought the car.

Im looking for an M42 to go in my e21, but its been rough finding a good donor. Ideally I would find a rolling shell to get all the necessary pieces.

I do not want to perform a rebuild to do the swap, that would put me way over budget for now. Nor do I want to swap in a motor that would need a rebuild in a few short years. While this is not a DD, I dont want to spend a lot of money on this.. just do it right without a rebuild.


Say this engine passes a compression test, what may be some indicators to say that its just had too many miles? Water pump was recently replaced, it hasnt been neglected. In general, is swapping in a high mileage car a bad idea?

This is my first swap, I look forward it to be a learning experience but not a 'I put in a bum engine' type experience :/

[bmwman91]

Honestly, don't do this unless you are at least willing to overhaul the timing chain assembly. That is one of the major fault areas of the engine. Parts will run you around $600 and it'll take a weekend if you are reasonably competent at wrenching. In fact, you really need to consider swapping in a late-model M42 timing case since the E30 design was flawed and later corrected in 1994. You can do this without pulling the head, although it is a big job and a pain in the ass (you also need to get the later model gaskets that go with the later model case).

Also, the other big design issue is with the crank thrust bearing. BMW only used a half shell, and it wears badly if you start the car with the clutch pressed in (you should never start a car with the clutch in if it doesn't force you to). No oil pressure plus 300lbs+ of axial force, that sort of thing. You can install a thrust bearing in the other half at that position to make it a full thrust surface as far as I know, but again that is a big job.

If you just want to buy it and drive it and not wrench on anything major, at least drop the lower oil pan and check for debris, AND check to make sure that the upper bolts inside the oil pan are not loose (they are known to fall out and cause an oil system failure).

[jaredmac11]

That's awesome information.
Is the timing chain assembly refresh a job I should do with most of these m42 on the e30? If so, I will need to adjust my budget accordingly, or just target the e36 m42 outright

Truth be told, I have avoided the E36 M42/M44 engine because the trans is a bit larger with the 265 over the 260 (though I hear the 265 is a better trans) and I know I will need an e30 oil pan to gain appropriate clearance. I dont know about the radiator, mounting arms, induction system, and other things. Just arent may swaps like this online..

That being said, those are pretty great selling points plus the e36 318 is muuuuuch more plentiful. and I could use it as a DD until the engine is in good shape.


Unfortunately this car cannot be driven, It was hit. He claims it runs and I should be able to verify this week. That adds to the complications...

[bmwman91]

The E30 timing case is a time bomb, period. It seems like many of them start to blow up at ~250k miles. Mine went at around 220k and I know of a number of others that had it happen.

An E36 M42 swap is probably also an option. Just make sure it is a 1994 or 1995 version since those had the improved timing case. You may still need to rebuild the timing chain assembly though, but at least the big case casting isn't going to break on you.

The E30 M42 uses a G240 tranny BTW. It is small and light. As far as I recall, the E36 M42 uses a G245 or G250, or something like that. Still small and light compared to the 6 cylinder ones.

[TobyB]

Yeah, the E36 trans is 1:1 in 5th. Thus, the E36 got a 3.44 diff.

I THINK the E36 5- speed is the same, M42 or M52, but don't quote me on that.

t

[jaredmac11]

Yeah, the E36 trans is 1:1 in 5th. Thus, the E36 got a 3.44 diff.

I THINK the E36 5- speed is the same, M42 or M52, but don't quote me on that.

t

I didnt know the e36 diff was that low. I have a limited slip diff with a 3.91 ratio. I am likely going for the e30 trans anyways for the fit but my diff would be pretty goofy in a e36 trans. Good info!