Crankshaft endplay

[Roysneon]

OK guys, I seriously need someone who knows what they're talking about to give me some good tech on the M42 crankshaft.

The motor is completely torn down to the timing case, head and rotating assembly being separate.

When I grab the crank and push/pull there is a 'click' sound and I can feel the crank hit its 'in' and 'out' limit. I don't have the proper tool to measure the play, but it's not a thing that I can move gradually or to the point where I could estimate it, it's too small for that.

How much is OK before I have to get new bearings and how long before I need a new crank? I don't have much interest in sourcing a new crank, buying rod and main bearings and new rod bolts, so if that sounds like way too much then I'm just gonna use another motor I have in stock and hope for the best. I really want to just re assemble the motor as is with new gaskets and call it a day. If I could just replace the bearings with a new set of 360 degree thrush bearing I would be willing to do that.

[Roysneon]

Sooo this might help someone give me a clue on this:















That's the #4 main/thrush bearing.

[bmwman91]

This is a fairly common thing on M42's actually. It isn't GOOD, but it is common. I believe that later ones (and the M50) used a 360 degree thrust bearing and that it is like a direct swap for an older M42. Ask around on here and M42Club for details since I am not 100% sure.

[Roysneon]

I've seen many threads about it already. I just don't know how bad is 'too' bad. Right now I'm still waiting on parts in the mail so the M42 won't be resealed and back together in the time frame I need my car in, so that idea is getting scrapped and I'm just throwing in another motor that I have and hoping for the best.

This motor will likely be built up into a supercharger setup or a high revving n/a motor for my track car since I'm robbing the M50 that was destined for it to get my dd back on the road.

[bmwman91]

Per one of the original M42 gurus:
Crankshaft : End play: 0.0031-0.0064"

http://www.esatclear.ie/~bpurcell/318isengine.html

I'd guesstimate, from your pictures, that your crank has something like 0.025" of play in it.

[carnurd]

My engine had a bad thrust surface, got it welded and nitrided professionally with a 360deg bearing, and now the crank play is almost non existent and spins really really nicely.

[Ryann]

I would definitely order a new 360˚ thrust bearing for your engine. If you are patient and careful you can roll that one out and roll a new one in without pulling the crank. Either way it definitely needs to be done.

[AndrewBird]

Go buy a cheapy set of feeler gauges and measure it correctly. Guessing on something like this is NOT the right thing to do.

http://www.harborfreight.com/32-piece-sae-metric-feeler-gauge-32214.html

[KenC]

If you can feel/hear it, it's too much. Get a new set of bearings and hope for the best.

[Roysneon]

I've got a new crank lined up that I will install later with new bearings and bolts. Won't be going in this car though, I threw my M50 in my daily so I guess it's M42 racecar by default.