Need advice from experience for an M42 rebuild

[bmwman91]

Cool, yup time to start looking for the dozen or so stupid little things that it normally is! Consistent compression should at least give you some peace of mind. Well, sort of. If it ends up being the crank damper, that's one that will hurt the wallet! It might be cheaper to convert to the E36 serpentine belt setup at that point.

[roguetoaster]

Compression test is about 180ish across all 4 cylinders. There was little to no variation between cylinders. This was without bringing up the temp.

Sounds good. Clearly it's time to hunt down the items mentioned above. Start with the crank damper, see if you can tell if it appears to maintain a constant gap at the back relative to some reference point as that's a good way to visually check for issues.

[JonsE30]

Compression test is about 180ish across all 4 cylinders. There was little to no variation between cylinders. This was without bringing up the temp.

[JonsE30]

Thanks guys. I’ll try to get my hands on a tester ASAP.

[roguetoaster]

I also cannot tell what that is from the sounds. However, it's always safe to do as suggested above. If you borrow a tester from an auto parts store do put some anti sieze on the threads of the hose fitting before threading it in.

[JonsE30]

Oh man me too. I would cry if I have to rebuild again. Sent from my iPhone using Tapatalk

[bmwman91]

-Hmm, yeah hard to say from the video. I've seen cars run worse from vacuum leaks and scrambled sensors, but I'd still do the compression test ASAP. You don't really need to warm it up since a cocked valve will probably show up very clearly if present, but I'll cross my fingers for you that it's something else!

Maybe also take a look at the crank damper wheel too. They get old and the rubber rung cracks, which can cause the outer toothed part to get wonky and the computer will lose track of the crank position.

[JonsE30]

Link: https://youtu.be/GuDuuvjzSow Here’s what it sounded like yesterday after readjusting the timing. Wire on the firewall is unplugged. I will need to check tomorrow morning on the plugs under the intake.

[bmwman91]

Well, I would say to warm it up and run a compression check just to rule-out the worst case scenario. Do you hear anything at all like a burble noise or bellowing noise? I am all too familiar with what a bent valve sounds like, and there is a somewhat distinctive sound when compression is lost. Another video could help, although the sound is usually low enough in frequency that phone mic's probably don't capture it well.

Otherwise, I'd say it could be vacuum leaks, or a bad sensor connection somewhere. Did you possibly mix up the coolant temp sensors? The grey connector goes on the one toward the front of the engine and the black one that is not part of the same branch goes on the rear one (the one on the same branch is for the oil pressure switch...I mixed those up once and got a real scare).

Also, did you happen to notice a single-wire connector that was unplugged up on the wire loom on the firewall and plug it back in? If so, it needs to remain unplugged and it has been the cause of some people's troubles in the past.

[JonsE30]

I tried starting it again and I didn’t see any more smoke. The car idles and catches itself but it doesn’t die. I let it run a little to get temp up but not too hot to check for any leaks. I found some seeping from the lower timing cover. Near the water pump and a/c compressor error. So I gotta deal with that too. Sent from my iPhone using Tapatalk

[bmwman91]

Well, there is at least some good news in there.

When you say that smoke was coming off of the head, where did it look like it was coming from? If you used gasket sealers then maybe those had some volatiles flashing off. Did the smoke stop after a little while, or was it continuous?

1215 can be a number of things, and usually not the AFM. The most common one is a big vacuum leak. Did the rough idle last for 30 seconds and then stop, or did it stall?

[JonsE30]

Those techniques all worked! I loosened all the front bolts that let me re-adjust the gears by a tooth or two. I squared off the edges of the rear of the camshafts then tightened everything down. I then hand cranked as recommended then lock flywheel again to remeasured. I had to do this a few times for those micro re-adjustments. Once I got it to stay flat after a few tries I slapped everything back on then tried to start and she fired up and she sounded “normal” without that clacking/slapping noise. There was light “steam” or light smoke coming from the head, but not like black smoke. Is this like the rebuild lube burning off or is something more serious? No white or black smoke was coming out of the muffler and when I gave it some gas the muffler sounded normal. For a maybe about 30 seconds or so it was rough idling but not dying, then a check engine light came on. I did the stomp test and it came with a 1215 which I read is the MAF sensor. Is this related to the rough idling? But this is means the engine rebuild is OK? Now it’s these other maintenance items to address outside the engine rebuild?

[bmwman91]

I loosened the front four bolts of the gear on the exhaust cam and tried to use and adjustable wrench to rotate the cam so I can level it with the squared off edge of the intake cam but It stopped. And I didn’t want to turn it more because I didn’t want risk snapping or breaking anything. Is this the resistance from the lobes pressing on the lifters? Should I just rotate with a little more force?

Some resistance is normal, and it may well feel sort of sticky. Also, it looked like both cams were off, so you will need to mess with both at the same time to get things parallel. Just be sure to lay some sort of straight edge across them to check that they are parallel...it can't be done reliably just by eyeballing things.

[roguetoaster]

There can be a lot of resistance when turning the cams as you have no mechanical advantage and you have to compress the valve springs. Use your best judgement and see where valves are in their travel relative to piston position to inform you if something may be wrong.

[roguetoaster]

Just to add, the cam bolts can be undone and somewhat tightened with a flat wrench, so no need for that other stuff.

You are at the checking and adjusting phase, so don't go back to disassembly unless you absolutely have to.