M42 Crankshaft play acceptable?

[StereoInstaller1]

Question here, guys: when I grab the flywheel and yank forward and back on this M42 block sitting here, the endplay on the crankshaft is just over 1/16''.

Is this the famed 180 degree thrust bearing nonsense?

I can't imagine this being acceptable on any motor, much less a BMW.

How much grief is it to change the thrust bearings on this thing?

Luke

[Ryann]

I don't know the exact m42 spec but typical maximum crankshaft endplay is usually more like 1/64" (.015-.016). I've heard from a couple different people now that the new main bearing set includes the updated 360˚ thrust bearing, and installation should be freakin' easy if the thing's already out of the car.

[KenC]

It does include it. I bought it.

You'll probably want to have the crankshaft inspected though to make sure it's still good.

[io_RobbieRodgers]

Yep. If you have your tranny off already, all you need to do to get the oil pan and crank out is drop your front subframe, easily done with the help of an engine support bar, which runs about $60 at Harbor freight. Rebuilding your crank is pricey though, runs about $200-$300 dollars because you have to replace all the rod/maincap bolts, and they aren't cheap. I found the best prices for this particular job at autohausaz.

At the minimum you'll need:

Upper and Lower Pan Gaskets
Front and rear crankshaft seals
Rear crankcase gasket
Main bearing shells
Rod Bearing Shells
Rod Bearing Bolts (x8)
Main Bearing Bolts (x10)
All those PIA Timing case gaskets

It's essentially a bitch and a half, and if you do it you might as well be rebuilding every other wear part on the crankcase while you have it apart, except for the cylinder head since you don't actually have to take that off, though you could.

[Martin C.]

Could this be simply a function of the rod bearings instead? Aren't those easier to replace if the engine is out?

[AndrewBird]

you have to replace all the rod/maincap bolts

Is this true? I'm assuming then they are stretch bolts?

[Ryann]

^No. The head bolts are the only engine fasteners that shouldn't be re-used.

[AndrewBird]

That's what I thought.

[io_RobbieRodgers]

Every write-up or forum thread I've googled stresses the fact that the rod bolts HAVE to be replaced, as they stretch out of spec when they're are torqued. The jury's still out on whether you have to replace the main cap bolts, some people say they've re-used them with no problems, but every discussion ends up saying replace them just to be safe.

If someone can show me proof positive other wise, for the love of God please share. I'm ordering the parts either tomorrow or tuesday and that info would save my wallet.

[Ryann]

You can replace them if you'd like, you'll only be out $30. You'll have to pull one and measure it before you order because there are 2 different lengths depending on the date of manufacture. As far as I've read though the m42 rod bolts are not stretch bolts until late '92. Not proof positive but check Pelican for rod bolt info e30 vs. e36 and you'll see special notes for stretch rod bolts for e36 and not e30.

[Myster-E]

^No. The head bolts are the only engine fasteners that shouldn't be re-used.

Im pretty sure you can't re-use rod bolts on a m42

[Ryann]

Although OT I PM'd twistednut, fairly certain he can clear this up for us.

edit: to add to the confusion some RealOEM research reveals the following:

e30 m42 conrod bolt part #'s are
11247589671 47mm
11241713342 53mm 'not suitable for two part conrod'

e36 m42 conrod bolt part #'s are
11241739728 44mm 9/92-9/94
11241713342 53mm up to 9/94 'not suitable for two part conrod'

[Dj Buttchug]

crankshaft endplay tolerance is no more than .012-.015. fwiw 360 thrust bearing install will usually yield the same amount of endplay give or take a coupe thousandths as m5x engines require almost the same endplay specs as m42

also rod bolts can be reused. they dont stretch much if at all. torque spec on connecting rod bolts is somewhere around 30 lb ft.

[nando]

^No. The head bolts are the only engine fasteners that shouldn't be re-used.

WRONG.

BMW rod bolts are TTY. you must replace them.

main cap bolts can be reused.

[nando]

also rod bolts can be reused. They dont stretch much if at all. Torque spec on connecting rod bolts is somewhere around 30 lb ft.

wrong.