AdamRebuildsEngines - M42 Rebuild Questions (with eventual write-up + pictures)

[AdamPlaysDrums]

The M42 in my '91 318i has bitten the dust... Initially I thought it was just a failed headgasket, which after some extensive cleaning revealed the usual crack when these heads overheat. Head was taken to a shop that said they could fix the crack, but after they cleaned and inspected it the crack went "just about all the way through the head", so the hunt has been on for a new cylinder head ever since (that was mid-March).

Apparently, cylinder heads on the cheap are nearly impossible to come by, but I was given a lead on a motor+transmission that a fellow E30 guy had pulled to do an LS swap (about 200k miles on it, but running well when pulled). However, said guy has been extremely hard to get a hold of, so I did some digging and ALSO found a cheap 1995 318is being sold nearby (181k miles). The body is straight but paint's in terrible shape, and the interior is entirely shot (if I end up going that route I'll be driving it home sitting on a folding chair).

SO: The original plan - Get e30 M42 and transmission, sell transmission (mine was never an issue and it's still in my car at the moment).
Then, put engine on a stand, disassemble, take block + head + valves + pistons to a local shop to have them deep-cleaned and have the head/block surfaces decked as necessary.
Once everything's cleaned, put engine back on a stand and re-assemble from the ground up with as many fresh wear parts and seals as possible, as well as the best of whatever isn't a wear item between my original M42 and the new-to-me one I'd pick up:

-All the gaskets that come in a headgasket kit
-Upper and lower oil pan seals
-Front and rear main seals
-Timing profile gaskets
-Helicoil valve cover bolt holes
-Timing system (whichever of the two engines has the better components)
-Rod and cam bearings
-Oil pump
-Thermostat/water pump
-Mess under the intake (did mine 3 years ago, would most likely reuse those hoses as they're still in good condition
-Fuel injectors (mine have been cleaned but may upgrade to 4-pintle Mustang injectors)
-Clutch
-Garagistic motor mounts


Now, that's only if I can get this M42 that's already been pulled. Otherwise, I would snag the E36 and swap its motor into my car, then sell the shell and transmission. From what I can tell, all the headgasket stuff I've already purchased is a direct fit, but in order to get the E36 M42 in my car it will need the E30 sump and oil pan, but otherwise that engine shouldn't need much else to get swapped in (and I would rebuild it in the same fashion as I would the E30 one).

I'm definitely working on a budget, and when this car is running it is my daily driver, so I'm trying to stick with the same engine to make the swap a quicker and easier project. The big questions I've got, after perusing several threads and doing a fair bit of googling, are:

Is there any benefit to swapping in an E36 M42 vs. sticking with the E30 engine? I'd assume power is identical but I don't know if any of the electronics or anything like that would be better (I know the timing is an upgrade thanks to no idler wheel in the E36)

If I were to swap the E36 M42 in, what exactly needs to be done to ensure that it runs properly in the E30?

Are there any other projects that it would make sense to do while I'm doing this engine work that I haven't already covered? My valve springs were good when pulled, all the timing components did look good, radiator was replaced when I did the mess under the intake a few years ago...

I've read through the Zen thread (https://www.r3vlimited.com/board/for...30-maintenance) as well as this thread about an E36 M42 (https://www.r3vlimited.com/board/for...m-e36-into-e30) which answered many of my original questions, although some clarification on a couple points would be nice, hence my post. Once I have a motor in hand I'll document all the work with pictures and everything as well as provide any Q&A that gets answered as I go along.

(Also, if I missed a thread somewhere would love to do some more reading on all this so please let me know.)

Thanks in advance for any and all input!

[Powling]

If you are in need of specific E36 M42 parts let me know - I picked up a whole engine locally (Toronto) last week and am stripping it for parts. Some stuff I'm keeping but other stuff I am letting go. I'd be willing to ship to you if you need something specific.

[bmwman91]

The 1994-1995 E36 M42 definitely does have an advantage. The timing case in those waffleswaffleswaffles snot have the stupid idler sprocket, and instead replaces it with another plastic guide. The idler sprocket is a notorious failure point, and while still somewhat rare, it is a thing. Also, the timing chain tensioner rail for the E30 M42 is basically NLA, but the one in the later timing case can still be found I think. You just need to buy the later case-to-block gasket and cover gaskets, but it is a bolt-on otherwise if you want to swap one onto an E30 M42.

[AdamPlaysDrums]

If you are in need of specific E36 M42 parts let me know - I picked up a whole engine locally (Toronto) last week and am stripping it for parts. Some stuff I'm keeping but other stuff I am letting go. I'd be willing to ship to you if you need something specific.

Awesome! Thanks a ton for that info. I'm taking a look at the donor car early this next week, I'll let you know if I go that route and need any bits.

[AdamPlaysDrums]

The 1994-1995 E36 M42 definitely does have an advantage. The timing case in those waffleswaffleswaffles snot have the stupid idler sprocket, and instead replaces it with another plastic guide. The idler sprocket is a notorious failure point, and while still somewhat rare, it is a thing. Also, the timing chain tensioner rail for the E30 M42 is basically NLA, but the one in the later timing case can still be found I think. You just need to buy the later case-to-block gasket and cover gaskets, but it is a bolt-on otherwise if you want to swap one onto an E30 M42.

That's what I had gathered from my reading too. My car went through so many prior owners and at least one other M42 in its long life, so I'm not sure if my block has been upgraded with the new timing setup or not (I haven't pulled all that apart quite yet). Thanks for confirming that though!

[e30sh]

. My car went through so many prior owners and at least one other M42 in its long life, so I'm not sure if my block has been upgraded with the new timing setup or not (I haven't pulled all that apart quite yet).

There is a casting date on the block. Early ones are above the starter, later ones are in the middle of the block. Sept 93 and newer have the updated case if original.

[AdamPlaysDrums]

There is a casting date on the block. Early ones are above the starter, later ones are in the middle of the block. Sept 93 and newer have the updated case if original.

Noted, awesome. When I pull everything this weekend I'll take a look at that.




Also, a new question: the E30 M42 valve cover bolt holes are notorious for losing their threads. I'd helicoiled my now-cracked head, but does anyone know if the way they threaded the valve cover holes changed for the E36 M42?

[e30sh]

The E 36 version doesn't seem to do it as bad. I have three 6mm heads and all of them are good. I don't know if it's a better design, or if the e36 318 is more of an appliance car and people just don't tinker with them as much. Replacing the hard rubber grommets on the valve cover bolts helps prevent stripping.

[AdamPlaysDrums]

The E 36 version doesn't seem to do it as bad. I have three 6mm heads and all of them are good. I don't know if it's a better design, or if the e36 318 is more of an appliance car and people just don't tinker with them as much. Replacing the hard rubber grommets on the valve cover bolts helps prevent stripping.

Now that's very good to hear. I assume I'll know if they need re-threading once I take it all apart and see if little metal bits come out with the screws, but it's nice to hear that's less of a possibility with this era of motor. Definitely have the new rubber grommets ready to go too.