M42 REBUILD parts?

[jimco2]

I'm going to go thru a '91 318is (M42)motor and am looking for recommendations as to what to replace. The car has 145k, runs great, but leaks oil like an old Corvair.
I'm going to do comp & leakdown , oil pressure chex,(prob. OK) pull the motor, do all the usual replace gaskets, seals, cam chain tens & guides,
oil & water pumps, rod & main bearings.(rings?)
Any suggestions as to what else is likely to need replaced would be muchly appreciated. Any experience with likelihood of guides worn?
What's the deal with cam removal tool - anyone had success doing this without one?
I just want a good reliable street car , so I am not necessarily looking for hop up type changes. But, since it is out and apart.........
Thanks ,
Jim

[PaulC]

What condition are the sprockets in? You hear a lot about replacing the sprockets and chain, but you also hear that they go 200K. Wheres it leaking oil from? If you can get some Hylomar that might help with sealing it up. If you have the head milled get the upper tc cover done with it. You want a water pump with a steel impeller. As for the internal parts and modifications I guess its a question of how much you want to spend and if its worth it on your DD, but I'm no expert on that either.

[peerless]

Here is my experience with rebuilding 2 M42's. One took 3 engines to make one good one.

We will start with the factory flaws and how they should be corrected.

1) Stamped steel chain guide. These fracture and break apart. Replace with upgraded dealer part, its a all nylon/plastic construction. You will need one new 45mm long bolt in conjunction with the new guide.

2) Steel oil pressure relief valve, aluminum front cover. The steel valve can seize causing a immediate loss of all oil pressure, good by engine. Replace with updated dealer part, made of nylon/plastic. Make sure you get the spring and spacer as well. The spring is slightly longer so it all a matched assembly. You will most likely want to replace the oil pump rotors, front pump cover and bolts. All of this is about $45.

3) Front chain cover. These are known for leaking profile gasksets. The rail that holds this gasket gets corroded and leaks. Every one notices when it leaks outside the block, but no one notices when it seeps behind the block. This creates a rust cavity potentially damaging the front face of the block. Expect to at a minimum to replace the front cover. If the block is damaged, you can surface the front face to clean up any rust damage. .015" MAX.

4) Main thrust bearing. The factory in all their wisdom decided to only use half a thrust bearing shell. This is not capable of handling the high rpm loads created by the M42. You will find the bearing to be rounded and burnt black. The crankshaft thrust surface must be inspected carefully. On the 2 engines I built one crank was scrap and the other barely within spec. To correct this problem you will want to replace with a full 360* thrust bearing. I do not know if the standard replacement bearings come with 2 halfs. I use the early eta M20 main bearing set and have the lower main caps custom machined so they fit. This not only gives me a full 360* thrust surface, it also gives me a full 360* oil groove for improved oiling to the rod bearings. As a note, I pulled the oil pan on a M42 with 80K miles, it already had thrust bearing material in the pan, along with 4 oil pan bolts.

5) Crank pulley. While the stock crank chain gear does not wear very much a new upgraded part is available from the dealer. It has 2 rubber rings molded into it. This helps keep harmonic vibrations in check. This may help prevent the oil pan bolts from backing out

6) Rod bearings, I use custom Clevite 77 NASCAR performance bearings. This is a upgrade, the stock peices should work just fine as well.

7) lock-tite all your upper oil pan bolts to prevent them from backing out. This is a big problem on the front 6 bolts that surround the gasket for the oil pump pick area of the pan gasket. When these back out and fall into the pan the gasket can push out and you lose oil pressure. See number 5.

Regarding valve guides, they should be fine as they have very little side laoding due to the valve train arrangement. I did not need a cam removal tool either. When loosening and tightening the cam tower bolts, take your time, do it slow and evenly. Remember the camshafts are hollow and can break easily.

If anyone tells you the stock M42 is a great engine, they are pulling your leg or don't know the M42 very well. The stock M42 is very self destructive.

I have pictures to back up every flaw I just described above. Everything I said above comes from direct experience with the M42 engine.

Expect to pay about $2,500+ in parts and machine work to properly rebuild the M42. If you need help/advice along the way just give me shout.

[jimco2]

m42 parts

Thanks! Excellent...
I've done a few 2002 M10 in the past and expected the M42 to have it's own
set of thinks to pay attention to.
Jim

[Sam Cogley]

peerless, where do you get the custom-machined bearing caps made? If I end up having to rebuild my M42 at some point, I'd like to upgrade that weak spot.

I have trouble visualizing this "half bearing" thing. Does anyone have a picture of the bearing design?

[peerless]

The new bearing sets come with the 360* thrust bearings. If you want to run a full 360* oil groove, you will need to have the caps machined to accept the older M20 bearings. The current stock design is only a 1/2 groove.

I have my caps machined by Metric Mechanic. Call and talk to Teddy to explain it in better terms.

As far as visualizing the half a thrust bearing look at the picture below, remove one of the thrust bearing halves and replace it with a standard bearing shell, now you would only have half a thrust bearing shell. And yes, believe it or not thats all you have supporting your crankshaft axial loads in the original stock setup. Pretty weak huh?

[SnPaC]

Here is my experience with rebuilding 2 M42's. One took 3 engines to make one good one.

We will start with the factory flaws and how they should be corrected.

1) Stamped steel chain guide. These fracture and break apart. Replace with upgraded dealer part, its a all nylon/plastic construction. You will need one new 45mm long bolt in conjunction with the new guide.

2) Steel oil pressure relief valve, aluminum front cover. The steel valve can seize causing a immediate loss of all oil pressure, good by engine. Replace with updated dealer part, made of nylon/plastic. Make sure you get the spring and spacer as well. The spring is slightly longer so it all a matched assembly. You will most likely want to replace the oil pump rotors, front pump cover and bolts. All of this is about $45.

3) Front chain cover. These are known for leaking profile gasksets. The rail that holds this gasket gets corroded and leaks. Every one notices when it leaks outside the block, but no one notices when it seeps behind the block. This creates a rust cavity potentially damaging the front face of the block. Expect to at a minimum to replace the front cover. If the block is damaged, you can surface the front face to clean up any rust damage. .015" MAX.

4) Main thrust bearing. The factory in all their wisdom decided to only use half a thrust bearing shell. This is not capable of handling the high rpm loads created by the M42. You will find the bearing to be rounded and burnt black. The crankshaft thrust surface must be inspected carefully. On the 2 engines I built one crank was scrap and the other barely within spec. To correct this problem you will want to replace with a full 360* thrust bearing. I do not know if the standard replacement bearings come with 2 halfs. I use the early eta M20 main bearing set and have the lower main caps custom machined so they fit. This not only gives me a full 360* thrust surface, it also gives me a full 360* oil groove for improved oiling to the rod bearings. As a note, I pulled the oil pan on a M42 with 80K miles, it already had thrust bearing material in the pan, along with 4 oil pan bolts.

5) Crank pulley. While the stock crank chain gear does not wear very much a new upgraded part is available from the dealer. It has 2 rubber rings molded into it. This helps keep harmonic vibrations in check. This may help prevent the oil pan bolts from backing out

6) Rod bearings, I use custom Clevite 77 NASCAR performance bearings. This is a upgrade, the stock peices should work just fine as well.

7) lock-tite all your upper oil pan bolts to prevent them from backing out. This is a big problem on the front 6 bolts that surround the gasket for the oil pump pick area of the pan gasket. When these back out and fall into the pan the gasket can push out and you lose oil pressure. See number 5.

Regarding valve guides, they should be fine as they have very little side laoding due to the valve train arrangement. I did not need a cam removal tool either. When loosening and tightening the cam tower bolts, take your time, do it slow and evenly. Remember the camshafts are hollow and can break easily.

If anyone tells you the stock M42 is a great engine, they are pulling your leg or don't know the M42 very well. The stock M42 is very self destructive.

I have pictures to back up every flaw I just described above. Everything I said above comes from direct experience with the M42 engine.

Expect to pay about $2,500+ in parts and machine work to properly rebuild the M42. If you need help/advice along the way just give me shout.

Thanks for the great info Robert. I just experienced the misfortune of having my timing chain fail. From the sound of it, it likely my motor is toast? Do you agree? Do you know of any reputable re builders who take these things into account on the East coast of should i just look for something used and take my chances?

[bmwpower]

I've got these if you need them.

[tonywonder]

Expect to pay about $2,500+ in parts and machine work to properly rebuild the M42. If you need help/advice along the way just give me shout.

so what pricing are we looking at just for factory flaw fixes? just parts and also parts and labor.

[getouth]

$2500.00 is right on the money.

[nando]

$2500.00 is right on the money.

yeah, that's S50 swap territory..

[KenC]

I just rebuilt one myself for less than a grand.

[nando]

I just rebuilt one myself for less than a grand.

the timing chain parts are like $800 by themselves.. so it must have been a light refresh for a grand.

[fiftytakedowns]

the timing chain parts are like $800 by themselves.. so it must have been a light refresh for a grand.

I was debating doing the timing chain parts, and it goes for like 300-450 if you source from all the right places (blunt/worldpac)

I decided to go M50 when mine goes. becuase of how it would be s50 territory.