M42 rebuild

[Diake]

Hello everybody,
I'm new in r3vlimited.com. I wanted to write a thread to document, step by step and precisely, the rebuild of my M42. I will not be fast or constantly updating it since it a free time project. The aim is to create a sort of guide (not a proper since I'm not a mechanic) which might be helpful to somebody in the future.

I start with the picture of the engine in the original condition!


Congratulation for the nice forum and thanks for the support!

Luca from Italy

[Diake]

Today I washed the block to eliminate the dirt and started removing all the accessories and engine mounts.





The plan is to:
- Change oil and water pump, making sure the oil pickup bolts are secured with Loctite
- Upgrade oil pressure relief valve to plastic one (less prone to get stuck)
- Change timing gears, chain, tensioner and guides (upgrading to plastic ones)
- Changing seals and gaskets
- Changing head bolts to ARP (Future turbo project, but at the moment I want to run it NA)
- Control bearings and trust bearing (consider upgrade to 360° trust bearing and block bearings)
- Check valve conditions and change valve oil seals.
- Upgrade oil pan to low profile Motorsport one
- Remove viscous fan to instal electric one

Any suggestion on other parts to change/upgrade?

[jrobie79]

are you taking the head off? valve stem seals, profile gasket, timing case gaskets, upgrading to the m44 timing case (with different timing case gasket)...

[Diake]

Yea, I was definitely considering those. What about the m44 timing case upgrade?

[jaredmac11]

For the M44 timing case upgrade, Youll want to ditch the timing sprocket (e30) for a guide. There are other improvements but this is most key. Getting those (likely) brittle chain guides out is most key. There are other improvements for the M44, but you can get a decent upgrade with the e36 M42 (1992-1995). The e36 M42 ditched that timing sprocket for a guide.

Prepare to spend a pretty penny here.. at least $200-400.

[bmwman91]

The M44 timing case has one major difference from the M42 timing case. It does not have the mounting bracket for the crank position sensor, so you would need a custom machined bracket for that, and it would need to be properly designed to ensure correct ignition timing. You can use the timing case from a 1994-1995 M42 engine without this issue, and it uses the plastic guide rail instead of the deflector sprocket (which is the main advantage).

[jaredmac11]

I think youre right in that there isnt much advantage to using the M44... I dont know where its coming from then.

I also thought it was any e36 M42, but it looks like youre right, the plastic rail to replace the deflection wheel started in 94.

Honestly though, I would rather spend my money on getting new pieces for the rail than on a timing case unless the parts fell on my lap. The deflection wheel cant be that bad right?

We're talking about $300+ in parts here for the rails alone, which absolutely should be replaced.

edit: The killer is the guide rail, pn 11311247483. I was lucky to find one for sale for $75 from someone who didnt understand that you can fit the M44 guide rail in to the E36 (and E30?) timing case with some hardware replacement.

[bmwman91]

I would actually recommend getting rid of the sprocket, despite the cost increase of the newer timing case (I have bought used ones for ~$70). Other than that, rebuilding it should not really cost more than the M42 case. The later case uses a different gasket between itself and the block (don't forget this!), but it is about the same price.

The only advantage of the M44 case is that the oil pump rotors are 20% thicker, meaning 20% more flow. This can be advantageous on a built up M42 with higher compression and hot cams where pressures and speeds are more severe between moving parts.

[Diake]

Updates:

Yesterday I have gone on with disassembly.


First of all, I have removed the head cover


I have removed the upper chain guide to remove the timing gears


Cams don't look to bad or scratched, according to me



Removed water thermostat housing and upper cover


I removed the cams with the method explained on Pelican parts. For the wondering, it is: https://www.pelicanparts.com/BMW/tec...ft-removal.htm


After removing the trays


Without the head


I've seen better looking pistons


Removed lower case and water pump. For those wondering there are two threaded holes where to screw the bolts in to remove the water pump. It took me forever before I realized it


All the parts stored

As suggested from you, I will upgrade to m42 e36 lower timing case, if I can find one.
The next steps will be removing oil filter housing an pump, oil pans and see internal conditions.

Thanks for your help and suggestion. Hope it is helpful or at least interesting

[Diake]

Final disassemble and doubts:

yesterday I completed the removal of oil pump, pan, pistons and crankshaft.


First, a detail of the cams and the bearing surface


Oil pans removed. No loose pump bolts


Sprocket removal. Had some troubles since the key is slightly damaged.


Oil pump housing removed


Some oxidation on the crank


Piston and cylinder


Worst cylinder


Crank came out easily



Bearings need to be changed


Strange abrasion on one bearing let me wonder about the trust bearing, which resulted to be severely consumed


Unfortunately also the crank resulted damaged, with a play of approximately 1.5mm

I will bring the parts to my mechanic and ask about what's better to do.
I wanted to ask you what do you think from the pictures and if the crank is to be scrapped, as I think.
In that case I might consider a stroker with M47d crank.

Thanks for your support and suggestions.

Cheers,

Luca

[bmwman91]

The thrust bearing setup on the E30 M42 is one of the known bad design choices. As you have found, they only used a half-shell for the thrust surface. As a consequence, crankshaft axial runout can become severe. A main cause of this is starting the engine with the clutch pedal pressed down...zero oil pressure and probably 1kN of axial force on the thrust surface. No good! Since there is no requirement to start this car with the clutch down, it is easy to avoid in the future.

If the thrust surface on the crank has deep grooves worn into it or it is severely worn such that the journal with is much too large, then the crank is probably not worth trying to fix.

Look into installing two thrust bearing halves so that you have the full 360 degrees of bearing surface. I cannot recall if any machining is required, but I think that it was a very straightforward modification (you could test fit the old one onto the other side).

The cylinder walls look OK, and if you had a shop do a light re-hone they should be good. You may need the next size up of rings, but that is for you to check with a mechanic.

Other than that, it looks like you are making good progress. Don't forget to get the newer timing case-to-block gasket to go with the E36 M42 timing case. It is not the same as the E30 one. Also pull the oil pressure relief valve assembly out of the timing case and inspect it. The original design was later updated to prevent it from seizing open, causing oil pressure loss. It is easy and relatively inexpensive to do the update, involving parts 5-8.

http://www.realoem.com/bmw/enUS/showparts?id=AF93-USA-10-1990-E30-BMW-318is&diagId=11_0504

Check the cylinder head for cracks, mainly between the exhaust valves of cylinders 2 & 3. It has been known to occur. If there are some small ones forming that have not yet fully failed, a competent welding shop should be able to fix those.

[jaredmac11]

For the uninitiated and under-informed, exactly what does a full thrust bearing look like? I heard the M50 bearings can fit the M42 and were not half shell but they looked identical. Either I was mistaken or I have no idea what half or full shell means.

[roguetoaster]

Instead of having a full oil gallery (groove) in just the lower half you have a contiguous oil gallery.

No one is quite sure why BMW originally specified a 180 degree oiling bearing instead of a full shell. It may have had to do with trying out a new methodology in engine building, or perhaps they thought that sufficient oil would reach the upper half (which it does under normal conditions), or perhaps they simply did not care about longevity after 5-10 years.

[jaredmac11]

That helps clear it up. And regarding the design... were talking about the same engineers that put a weepy/leaky power steering reservoir RIGHT OVER an alternator on half their engines.

[TobyB]

I've seen better looking pistons

Looks like it has been detonating.

what does a full thrust bearing look like?

The bearing has thrust surfaces on shell halves.
If the wear can be polished or ground oversize successfully,
you'll be ok. And 'successfully' doesn't mean perfect, just
good enough to bear thrust and not allow movement.
Unlike the main surfaces, you can get away with some residual damage.

t