I've never taken a bottom end apart before, and I just bought 10:1 pistons. Here we go...

I need to learn not to poke around eBay when I'm trying to save money, because I just picked up an extremely rare set of BMW M30 factory 10:1 pistons and rods frow a low-mile motor for $160...which is usually what one used piston goes for.

I was back and forth between swapping in an M30B35 or building the original B34 that's in my car now, and I guess that decision has been made. Engine work beyond removing a head to give to someone else has always intimidated me, but I suppose now is as good of a time as any to learn. Ultimate scope of the project will be to install the hi-comp pistons and freshen up the bottom end while installing a windage tray, and also have some minor head work done while installing a new cam. I will probably buy a spare head to send off and get worked on but I will be building from the existing 340k (strong running, non-oil burning) shortblock in the car.

What should I have handy before doing this? What books do I read? Setting ring gap terrifies me. Is it worth paying someone else to assemble the shortblock? Am I good with a ball hone and new rings or do I pay a machine shop to do it? I see fancy coated rod and main bearings available, is there any merit to that kind of stuff? HELP ME!

I try to recommend to people to start with a completely spare engine if at all possible.  This way they keep the current engine in, and their ride on the road.

Do some machine shop shopping.   Look for a machine shop who has experience with the BMW engine, it often makes things easier.   As to setting ring gaps, that is easy - time consuming, but easy.   Use one of your old pistons to set the rings into the bores.

I prefer to have a very high quality machine shop do the bottom end assembly,  they are setting clearances with gauges, and tools, while you have Plastigage (useful, but not as good as the right equipment) .    Coated bearings are unnecessary, proper bearing clearances far more necessary.

I would recommend new rod bolts....

Maybe get a simple POS engine from craigslist to start with so you get your hands on experience first, without destroying that very expensive German engine

BMW M30s are $400-600 these days and about as complex as a Toyota 22RE, so I’m not that worried about it.

Shopping for a machine shop...  Here in central Texas it's good luck even finding one.  They seem to have gone the way of bookstores.

You live in mke right? Look up Jenny Morgan. She wrote a column for the BMW cca roundel magazine and I think has a soft spot for e28s (and issettas). She may be willing to watch over your shoulder as you do the work, or at least hook you up with someone who can do the same. I met her once at road America and exchanged a few emails with her. She's a legend in the BMW world for good reason.

pointofdeparture said:

BMW M30s are $400-600 these days and about as complex as a Toyota 22RE, so I’m not that worried about it.

But you don’t want to gack those rare pistons. I’d assemble a trash motor and see if you can get it to run on a stand then dismantle and check your work. 

Ring gap isn't tough.  Just install them and square them in the bore by sliding the piston against them.  Measure the gap and file as necessary.  I think you'll find that most of them are already really close.

My trouble is installing them; getting the gaps opposite each other and compressing them in the right orientation on the piston.

Are the pistons oversize or standard?  If they're oversize you need to have a machine shop bore and hone to match.  If they're standard, you need to keep the standard bore which could be iffy depending on how much wear is in the bores.  They wear more on the thrust side.  If you hone, use a three-leg stone instead of a bottle brush.  The stone will reveal high and low spots.  If it hones evenly, I'd risk it.  If you have worn spots I would consider machine shop or you will likely have unpredictable oil burning and uneven compression.

Long story short, you could just find a machine shop and get their recommendations.  Maybe they can hone it and you're good.  BMW blocks have a modestly high nickel content so you might get lucky.

Worst case is boring and sleeving

Robbie said:

You live in mke right? Look up Jenny Morgan. She wrote a column for the BMW cca roundel magazine and I think has a soft spot for e28s (and issettas). She may be willing to watch over your shoulder as you do the work, or at least hook you up with someone who can do the same. I met her once at road America and exchanged a few emails with her. She's a legend in the BMW world for good reason.

She was one of the ones that started this place, when it was the Little Car Shop. I have no idea if she's still involved, though.

Bimmerheads in LA builds these all day long.