(Yet another) M42 top end refresh and engine reseal (mid-2021)

[bmwman91]

The M42 is a funny thing. The two main weaknesses in it, namely the timing chain sprocket and the half-shell thrust bearing, are totally fixable, although both are a lot of work. The profile gasket used to be "the" thing that the engine caught flak for, but I think that basically all M42's that still run had it fixed long long ago. The real issue is the fact that critical timing components are out of production, and it looks like new crank dampers are also going to be hard to come by (if not NLA already). The dampers do seem to have a finite life, and at least in my case, that life was up until ~2020 lol. I drove the snot out of the engine though, so maybe that contributed. Others have also had it come apart.

It is a really cool little engine, really. The only distributorless engine to come factory in an E30, good fuel economy, reasonable performance with a decent chip and a light flywheel...and a nice light front end. It'll never have the same sort of mass following as the M20, but it is good that these days people are not buying them specifically for M/S5x swaps like they used to.

[eternal24k]

I agree, the M42 was never something I desired, I only bought my first 318i to swap the motor, but fell in love with the combo and ended up buying a second to swap just so I could keep the M42.
But the leaky M42 and questionable reliability has me thinking about throwing a Honda motor in to keep the things I love about the M42 without everything I hate.

But I have always wanted a 2002 with an M42....

[jsnppp]

Fantastic thread, making forums great again!

I have been so torn on my M42, I am not sure if this motivates me to refresh or k swap, but it's I love it regardless.

I feel late to the e30 party overall, let alone the M42 party. You, me and a handful of other folks are the only ones reading this thread :-)

I'm a huge 2002 fan (and longtime owner). The 318is has been described as the 2002Tii of the 90s and I agree with that statement. I no longer lust after the fastest. Just give me a nice looking, simple car that is fun to drive and gets good gas mileage!

[eternal24k]

Fantastic thread, making forums great again!

I have been so torn on my M42, I am not sure if this motivates me to refresh or k swap, but it's I love it regardless.

[jsnppp]

This weekend I plan to complete "Phase 1" of the reinstallation. Lower timing case, lower timing case cover, all internals + chain. Woot!

[jsnppp]

I didn't read through your whole post, I apologize. Did you check for crankshaft endplay? This bit me recently on my $400 m42 with similar mileage.

Hi - I did not check for crankshaft endplay. I'll look into it - I have the cylinder head off and front timing case, and both oil pans removed. Hopefully this can be done in the car?

Appreciate the tip.

~~~ UPDATE 9/16/21

I read into crank endplay and its not something that is easier at this stage of my profile gasket replacement and engine reseal. Endplay will be something to check when I replace the rear main seal and remove the transmission. Ideally the motor is out at that time too.

Wish there was a way to see if there was some play - I tried moving the crankshaft laterally and axially by hand :-). No movement but I don't believe that tells me anything (or maybe it's fine, who knows).

Anyway, thanks again for the heads up.

[NC325iC]

I didn't read through your whole post, I apologize. Did you check for crankshaft endplay? This bit me recently on my $400 m42 with similar mileage.

[jsnppp]

I'm close to reinstalling everything. Waiting on lower timing case gasket.

In the meantime I'm concerned about potential interference b/w valves and cylinders. I had the head deck out of due course. They shaved a tiny bit.

I prefer not to go through the loop of plastigauge if I can help it and am wondering if anyone can provide guidance on whether I should be concerned about it.

Final head:



A straight edge across the top, valves not crossing the barrier. Somewhat crappy photo.



A side view.

[jsnppp]

Today had other distractions, but on the white car I chased all block and head threads. Prepping for the big install (soon).



Also pulled the exhaust, to be replaced with a new Bre. Wish OE was still available. Spent time cleaning the engine bay too. It's finally getting to where I want it.

[jsnppp]

In this case I don't think they're too concerned about getting it done soon. Might be a few years before it gets done. Such a niche part now, I take it to be more a """"redesign"""" when it's quiet and they want the work experience kid to do something.

Assuming all other dimensions are the same, another future option is to build a brass/aluminum/steel bushing to accommodate the delta in post diameters.

[econti]

In this case I don't think they're too concerned about getting it done soon. Might be a few years before it gets done. Such a niche part now, I take it to be more a """"redesign"""" when it's quiet and they want the work experience kid to do something.

[jsnppp]

It looks like all of the areas where gaskets seal the coolant passages are fine, so I would leave it alone. Trying to level it with JB Weld won't really do much to benefit anything, and chunks might even pop off over time from the difference in thermal expansion rate between the block and the epoxy. As long as the cylinder jackets are not also pitted really badly, you should be fine to put it back together since it looks like you did a thorough cleaning.

Awesome, great confirmation, thank you bmwman91

[bmwman91]

It looks like all of the areas where gaskets seal the coolant passages are fine, so I would leave it alone. Trying to level it with JB Weld won't really do much to benefit anything, and chunks might even pop off over time from the difference in thermal expansion rate between the block and the epoxy. As long as the cylinder jackets are not also pitted really badly, you should be fine to put it back together since it looks like you did a thorough cleaning.

[jsnppp]

Anyone have thoughts on whether I should do something about the corrosion on the front of the block? I'm tempted to leave it, but could also thin skim it with JB Weld..

[bmwman91]

Good luck. They are undergoing a redesign from BMW head office and I could not find any aftermarket manufacturers. I had to search for a loooong time to find one for mine.

Great writeup though.

Do you mean that BMW is issuing a new/updated design for this part, and production on the old one has stopped in the interim? I know that the part is currently NLA, but it would be pretty cool if they were going to release a newer part.