Crankshaft Thrust Surface

[NC325iC]

So today I dug deeper into my $400 m42 and pulled the crankshaft. I had suspected that I had some thrust bearing issues when gave the balancer a bit of a tug and it moved probably close to 1-2mm. Well that was confirmed today.

The aft side of the thrust bearing is chewed up along the radius where the bearing wraps around the journal. This fits with the scuffing on the fore side of cylinder 3, all other cylinder are clean. As the bearing didn't wear through I am not overly concerned with the block, however I am worried about the crankshaft. Which brings me to todays post topic.

The aft thrust surface of the crankshaft is recessed from the casting by roughly 1mm (to my eye). The fore thrust surface is proud from the casting by roughly 1mm. Is the aft thrust surface supposed to be proud from the casting?
If it has worn to being recessed that would account for the play that I found.

At any rate I will be looking for a crankshaft. bonus question can m42 pistons be used with an m44 crankshaft for any benefit? (I am searching as well)

[varg]

Common problem with M42s, if the thrust surface has wear scars or is not perpendicular to the the main journals the crank is junk. I'd guess it is. M44 crank in a stock bore M42 makes a 1.9L stroker, not much benefit to the extra 100cc or so. There may be a piston skirt clearance issue with M42 pistons. Seek knowledge on M42club, lots of it there.

[NC325iC]

That's what I figured. It almost looks like someone used the wrong clutch stack up and the 180* thrust machined away the crank. I'll try to grab a good one on eBay or on here if anyone has one.

[NC325iC]

http://www.m42club.com/forum/index.php?topic=14948.0

This, exactly this

[bmwman91]

As a note, NEVER start the engine with the clutch depressed. There is no sensor/switch to prevent the car from starting with the clutch engaged so there is ZERO reason to hold the clutch pedal down when starting. As you have found, the half-shell thrust bearing is an oversight by BMW, and starting the car with zero oil pressure and full pressure plate force on the thrust face makes for big problems.

You can pretty easily convert to proper double thrust bearings as far as I am aware. I had my engine rebuilt that way. Others on here have made the upgrade as well, although I can't recall if any other work besides dropping it in is needed.

[NC325iC]

Sound advice for engine health.

I bought the engine in running condition, guy was going to swap in a k series honda motor. I decided to take the head off and check the bores, found some scuffing but no major scratches. I decided to have the cylinders honed at the very least so I pulled the pistons/crank. Glad I did.

this is sort of an interim engine plan for my 2002 so I'm not going full bore on the rebuild. Trying to keep things reasonable on cost and time.

Plans are now:
Hone the cylinders Clean the rest (head, pistons, lifters etc...)
New bearings (rods and mains w/360 thrust)
New rings Late m42 timing case
New guides
Maybe new chain


I Was looking for an m20 when I found this engine. Honestly, finding out how support for these engines seems to be dying out (timing components) I kinda wish I hadn't found this one. But it will be an easier swap in the '02 and keep nose weight down, not that I was worried about it. At any rate it's been fun to tear apart.

[bmwman91]

Yes it is unfortunate how the M42's critical parts are going NLA. The M44 should have at least a few more years of support, and if you are going to do a full build, I recommend swapping on an M44 timing case anyway. You will need a custom machined bracket to hold the crank position sensor, but other than that it is a bolt-on. Metric Mechanic (who built my 2.1L "Rally" M42) sells a bracket.

[NC325iC]

The m44 case is tempting because used ones are so much cheaper. But I don't see any other benefit really. A bit higher oil flow won't be a huge deal in a basic rebuild. The late 42 case might cost a bit more but with the bracket factored in it's probably a push.

[bmwman91]

The m44 case is tempting because used ones are so much cheaper. But I don't see any other benefit really. A bit higher oil flow won't be a huge deal in a basic rebuild. The late 42 case might cost a bit more but with the bracket factored in it's probably a push.

Yeah, other than the NLA M42 tensioner parts we are discussing in the other thread, there is not that much advantage to the M44 timing case.