Older m30 - rebuild questions

[Chells_88ix]

Euroshark, I am hoping you are correct. My e30 is sitting with the head off right now waiting for another to go back on, one of the rocker arms shattered. After picking out all of the pieces we went ahead and pulled the head to see if any had gotten into the cylinders and they all look pretty good to me, I couldn't feel any cuts or distinct wear in them. But when we did a compression test the cylinders were a bit lower than normal, what effect would the rocker being broke have on that test, any? I believe the valve was stuck in a partially open position. After reading this thread should I delay the reinstall and do the things you have recommended to this person. Glad you asked this question :). Thanks, michelle

[Lurker27]

Very encouraging - I knew they were bulletproof! I'll check out the compression test and do bearings/seals for sure. Thanks guys.

[Doughnut]

I always learn somethin from euroshark, haha

+1, he knows his shit!

And euroshark, my m30b35 was the same, near 250 000km on the clock when pulled from the donor car and still had its cross hatching on the cylinder walls.

[euroshark]

That's what I am hoping for, I don't own an E30 so the only place on this forum that I am useful is here in the M30 section!

[JoeMadoo]

I always learn somethin from euroshark, haha

[euroshark]

If you want to do the bottom end I would go ahead and do:

Front and rear main seals
Main bearings
Rod bearings
Thrust washer
Rings
Oil pump chain
Timing chain (especially because of the mileage - they stretch over time)
Gaskets of course

The cool thing about M30s is that as long as there is no damage to the crank you can usually throw standard size bearings in and put it together. Since the cranks are forged they should only be polished if anything, not machined (this is per BMWs recommendation). The main timing chains don't generally break even with super high mileage, but they do stretch over time and this will cause the cam timing to retard causing it to feel low on power. For rings you might be able to get away with just using a flex or ball hone and roughing up the bores a bit before you install new ones. The iron BMW used in M10 and M30 blocks is seriously some of the hardest iron EVER. Machine shops who know better will charge extra for boring these blocks because they tear up tools, so chances are there will be little to no wear in the cylinders. You might even see the original machining marks! My 225,000 mile block that I opened up recently had cross hatching in all 6 cylinders... They are super tough.

[E30SPDFRK]

If the compression is good and you don't hear any knocking, it should be fine. If you still want to rebuild it just for piece of mind, I would do at a minimum rings, bearings and honing. The rest is up to you how involved you want to get.

[Lurker27]

I've got a bead on a 91 e34, with 5 speed. The head has been rebuilt is the last 50k miles, and the guy says it burns no oil (I haven't driven it yet to evaluate power) and has recent compression/leakdown tests, ostensibly with good results. The rest has nearly 300k on it.

For a rebuild on this one, I'd want to do rear main seal, bearings on the bottom end, and maybe rings (not sure if rings are needed if compression/leakdown is good). I'm not sure exactly what pieces are needed - I have the manuals but haven't leafed through them yet. I'll eventually be going turbo.

Any input is appreciated.