How bullet proof are the M42 engines?

[Cobra Jet]

Just how bullet proof are the M42 engines?

I know they have forged internals and such, but for the most part, has anyone ever popped a piston through the side of the block or totally destroyed the internals?

I've read many many threads regarding certain failures that can occur with these engines, but for the most part it seems complete engine failures are more attributed to lack of owner maintenance, such as:

1) OVER HEATING (which also seems to be the #1 premature cause of most M42 engine failures) - which can be due to: profile gasket failure, head gasket failure, water pump failure, multiple coolant/heater hose failures and/or radiator failure

2) loose bolts found in oil pan, which could ruin oil pump and cause other issues

3) timing chain - worn out cam gears, worn out timing tensioner, worn out chain, worn out sprockets, worn out timing chain guide rails, etc

Even with the above failures, it seems the block & lower internals are often unaffected and the engine can easily be "rebuilt" for a marginal sum of $.  I have yet to come across a thread where an M42's lower half has detonated, caused major failure and/or has obliterated pistons, piston walls, bent rods, blown holes in block walls, broken cranks, etc. rendering the entire engine useless of which nothing could be salvaged from said engine.  From what I have read on this site and multiple other BMW sites, it just seems that most of the failures occur at the top side, rather than the bottom...  true or false?


Would all of you say that for the most part, the M42 is an extremely durable engine for use as daily driving?

If all preventive maintenance is addressed by the owner or previous owner(s), should these engines last well into the 300k+ mileage range without needing a rebuild or experiencing major internal failures?

What other MAJOR events or issues could cause internal engine failure for the M42?

Even if an M42 is "beat on", to what extent of abuse can it take before the internals fail?

[sheepdog]

From what I have seen, it is pretty stout really.
Nothing really stands out as week spot other than what you have already mentioned.

Yes, people have blown out the bottom end, but usually it is lack of maintenance either on their part or the previous owner. Same with the chains. The only thing really bad is the bolts (and possibly the thrust bearing).

Yes, these motors have gone well into the 300k+ range.

[colin86325]

Mine punched a hole in the block about an hour after I bought it.  It had been making a rattling noise, so I knew I was going to have to rebuild it anyway. i haven't gotten a chance to determine what led to the failure.

Here are some pics:
http://www.e30tech.com/forum/showthread.php?t=54136

[John W]

A lot of engines from cars built in this era (late 80s/early 90s) will last just as long or longer without major work as the M42.

There are some issues that tend to rear their head around the 120-150k mile mark (timing gear, oil pan bolts) can lead to major $$ if not addressed before it's too late. The good thing about the m42 is that these problems have been well documented and can be anticipated.

With luck and a careful eye for maintenance and potential problems, you might see 300k miles (realistically probably more like 200k for some of the cylinder head internals), but at that point you probably will have pulled the oil pan to retighten bolts a few times, replaced a timing chain or two and replaced several timing chain tensioners. And this is a best-case scenario.

[nomad]

sure, if you omit the problem areas then there's nothing else really wrong with them. But as was mentioned, other engines of the same vintage will last just as long, and i'd venture to guess they'd do it with less tlc. This engine is good, but it must be taken care of. That can probably be said for a lot of engines though. There are others that will take a lot of abuse and keep going.

[Cobra Jet]

Supposing one fixes or addresses the known M42 issues (as noted above and in many threads on this site) which would prevent a premature major M42 failure, how long do the forged internals really last before needing to go through a complete shortblock rebuild?

Many M42 owners have already experienced or have had to deal with the upper rebuilds due to overheating issues (head and/or associated valvetrain replacement), then there is the R&Ring of all of the timing chain components, replacing necessary gaskets for those areas, etc...  So, with that in mind, since the top half has been gone through, how long would one suspect the bottom would last before needing to go through it and rebuild it as well (boring or honing of cylinder walls, possibly going up a piston size if the block needed work, rods, bearings, etc)?

I know folks also use forced induction on these engines as well (blowers, turbos, etc), however, I'm only asking the questions pertaining to a naturally aspirated M42 that sees daily driving - no racing, auto crossing, road racing, etc...  it seems the bottom end of the M42 is pretty stout with the forged internals, correct?  I guess what I am asking is how long would one suspect an M42 bottom end to last before having to disassemble the entire block & internals for replacement (again, assuming one has not blown up the engine and it has had proper maintenance)?

[sheepdog]

Supposing one fixes or addresses the known M42 issues (as noted above and in many threads on this site) which would prevent a premature major M42 failure, how long do the forged internals really last before needing to go through a complete shortblock rebuild?

I don't think anyone really knows, but I have seen a few with over 350k.

For some reason cars of this era have not had the mileage put on them that slightly newer cars have. As you go back through the decades, the older the car is, the fewer miles put on them per year.

[sijef]

I have a '93 e36 with the M42.
I'm second owner (its my second car to an e34 540i and a daily driver).
First owner is a good buddy who took great care of the car and gave it to me after nicking a wall with it. I put it all back together.
It has now passed through the 270k mile mark on just regular, but attentive maintenence. Overheated once due to cracked radiator from the accident that I did not catch during the rebuild ... but NO engine damage. Everything inside that motor is original (I added in a Dinan ECU chip when they were on sale).
In fact, the motor outlasted the tranny!
Burns 1/2 quart of oil in about 3.5k miles ... or within one oil change. Runs, pulls excellent, smooth and quiet. It will easily reach the 350k mark before it will need any major maintenence. Try that with a Camry .......

I'd buy another M42 bimmer in a New York minute!

[D. Clay]

They have a barely adequate thrust bearing. Keep your foot off the clutch - it's not a dead pedal.

[mgold]

Mine is just about to hit 210k.  I've had the intake manifold gasket replaced once, valve cover gasket, water pump twice (2nd time was preventative maintenance), an alternator, and an AC compressor.  I'll probably be replacing the chain tensioner soon, but otherwise it just runs and runs.  Burns about a quart between oil changes, but that's about it.