Removing Crankshaft

[master quon]

Hey guys, so long story short the rod bearings need to be replaced for M20B25. I already have the head and oil pan off. I'm wanting to take the crankshaft out to take it to the machine shop. I have a few questions before I dig in:

1. It looks like the crank bolt needs to be removed to get the front housing off, is that correct?

2. If I remember correctly when I did the auto to manual swap, the rear housing is just held there by the flywheel. Removing the flywheel should free up the rear housing, correct?

3. Besides the rod bearings and housings, is there anything else holding the crankshaft to the engine?

4. Should I be asking anything specific from the machine shop?

5. I want to remove the pistons just outta curiosity, I've never done that before. Good idea? Bad idea? Can I get them back in without scoring the walls or getting the block honed?

6. Lastly, I have a bad "while you're there" mentality, I'm sure you all feel me there lol. I already have the parts for a complete head rebuild (272 cam, new springs, new valves, etc...), would it be worth it to just go the distance and do a bottom end rebuild as well? Let's say a budget of $1500 for bottom end only. I like hp gains, so i'm open to increasing displacement, or whatever you'd suggest (btw not looking for an engine swap for hp gains, I like my M20 :)).

Sorry for all the questions. Thanks a bunch fellas.

[Steve o 77]

Hey guys, so long story short the rod bearings need to be replaced for M20B25. I already have the head and oil pan off. I'm wanting to take the crankshaft out to take it to the machine shop. I have a few questions before I dig in:

1. It looks like the crank bolt needs to be removed to get the front housing off, is that correct?

Yes. big air powered 1/2" drive impact should do nicely.

2. If I remember correctly when I did the auto to manual swap, the rear housing is just held there by the flywheel. Removing the flywheel should free up the rear housing, correct?

sorta. It's held on by 4 or 5 bolts, easy to remove once the flywheel is off though.

3. Besides the rod bearings and housings, is there anything else holding the crankshaft to the engine?

Nope, just need to pull the oil pump, rods disconnected and caps removed. You can leave the pistons in the bores if you're not replacing the rings. Then remove the main caps and it should pop right out.

I would just replace the rod bearings while you're in there by the way if you can swing it.

4. Should I be asking anything specific from the machine shop?

Have them clean it up, mic the journals and compare sizes to the spec, and micropolish if needed.

If one or more of the journals is out of spec scrap the crank and find a good used one. Don't let them talk you into grinding it, BMW cranks are hardened so the hardening must be "removed" before grinding, then "re-applied" after. This will cost you a ridiculous amount of money compared to finding a good used crank.

5. I want to remove the pistons just outta curiosity, I've never done that before. Good idea? Bad idea? Can I get them back in without scoring the walls or getting the block honed?

If you pull the pistons you might as well hone the cylinders and throw new rings in it, it's up to you.

You absolutely can remove them and re-install without issue though, you'll just need a ring compressor.

6. Lastly, I have a bad "while you're there" mentality, I'm sure you all feel me there lol. I already have the parts for a complete head rebuild (272 cam, new springs, new valves, etc...), would it be worth it to just go the distance and do a bottom end rebuild as well? Let's say a budget of $1500 for bottom end only. I like hp gains, so i'm open to increasing displacement, or whatever you'd suggest (btw not looking for an engine swap for hp gains, I like my M20 :)).

Oooohh I understand this lol. If you're resourceful you can get a pretty good setup for that money. I'm pretty new to this game but if I were you I'd find a cheap M20B27 crank and some SETA pistons to make you a cheap 2.7i. Again I'm new too so this might not be the best option.

Sorry for all the questions. Thanks a bunch fellas.

.

[jeffnhiscars]

Unless there is zero lip at the top of your bore (highly unlikely)you will need a ridge reamear to remove it or you will crack your ring lands. Note I did not say might..but will. AMHIK