Rebuilding an M20

[Jand3rson]

I remembered today that I've got the M20 block from my white 89 325i parts car sitting in my backyard still, wrapped in plastic and covered up. My plan now is to rebuild that motor over the winter and buy a 325i or e with like a not-well running engine or high milegage, but with a nice body and interior, then spend the rest of what I have saved for suspension and wheels. Then in the spring, I can drop the fresh new engine in.

The motor ran GREAT while it was in the car, but had close to 300k miles, and had some damage to the top of one of the pistons, I think from the end of a spark plug falling into the cylinder, and bouncing around, because the head had the same damage in the same cylinder. I'm thinking that what I will do is replace all the internals, have the cylinder walls and top deck refinished, and just really build up a nice new motor overall. I'll also get a new head and do it up the same way.

What I'm wondering, is should I just replace everything intenally? I plan to replace the pistons, but should I do the crank, rods, and all that stuff while I'm in there? I figure I might as well, unless the parts are still good to use, but I think that after 300k, it won't hurt to replace most of the parts.

And by the way, I don't want any "don't waste your time rebuilding an M20, they are weak, blah blah blah". I like the M20, I know quite a bit about it, and with the right internal and head work, it will be PLENTY fast for me. I'm not out to build an M3 killer.

[Spaz]

well start with,

bottom end
- rod bearings
- main bearings
- all the piston rings
- pistons (becuase of damage)
- all the gaskets
- oil pump shaft bearings
- check the oil pump for wear and possibly replace that
- have the crank polished, check for warpage, cracks
- have the block hot tanked, check for warpage, cracks

top end
- head surfaced, check for cracks, and warpage
- replace cam bearings
- rocker arm shafts
- rocker arms
- check all the valves and seats for wear, replace as nessary otherwise, perform a valve grind.
- check spring tenison, if within spec keep, if not replace.
- all the top end gaskets
- have the cam checked over, (pitting, cracks, out of round, etc.)

The rest
-t belt.
-water pump
-tenisoner
-drive belts
-intake/exhuast gaskets
- coolant hoses
....blah blah blah
you know the rest.

this is all off the top of my head, i can get you a replacement list from when i was going to rebuild my engine.....

if u need more info let me know

-cam


btw u going to stroke it?

[Jand3rson]

well start with,

bottom end
- rod bearings
- main bearings
- all the piston rings
- pistons (becuase of damage)
- all the gaskets
- oil pump shaft bearings
- check the oil pump for wear and possibly replace that
- have the crank polished, check for warpage, cracks
- have the block hot tanked, check for warpage, cracks

top end
- head surfaced, check for cracks, and warpage
- replace cam bearings
- rocker arm shafts
- rocker arms
- check all the valves and seats for wear, replace as nessary otherwise, perform a valve grind.
- check spring tenison, if within spec keep, if not replace.
- all the top end gaskets
- have the cam checked over, (pitting, cracks, out of round, etc.)

The rest
-t belt.
-water pump
-tenisoner
-drive belts
-intake/exhuast gaskets
- coolant hoses
....blah blah blah
you know the rest.

this is all off the top of my head, i can get you a replacement list from when i was going to rebuild my engine.....

if u need more info let me know

-cam


btw u going to stroke it?

Great list Cam, thanks a lot. I'm not going to stroke it, because it's a 325i block, and not an e.

[Jon325i]

You know Josh if you're going to completely tear this thing down, maybe you can try to source up the right combo of Eta crank, rods and pistons (those bits should just drop right in). A 2.7L on the cheap....and it should be straight forward stuff to do with everything in pieces.

Just a thought.

Jon

[James Crivellone]

well start with,

bottom end
- rod bearings
- main bearings
- all the piston rings
- pistons (becuase of damage)
- all the gaskets
- oil pump shaft bearings
- check the oil pump for wear and possibly replace that
- have the crank polished, check for warpage, cracks
- have the block hot tanked, check for warpage, cracks

top end
- head surfaced, check for cracks, and warpage
- replace cam bearings
- rocker arm shafts
- rocker arms
- check all the valves and seats for wear, replace as nessary otherwise, perform a valve grind.
- check spring tenison, if within spec keep, if not replace.
- all the top end gaskets
- have the cam checked over, (pitting, cracks, out of round, etc.)

The rest
-t belt.
-water pump
-tenisoner
-drive belts
-intake/exhuast gaskets
- coolant hoses
....blah blah blah
you know the rest.

this is all off the top of my head, i can get you a replacement list from when i was going to rebuild my engine.....

if u need more info let me know

-cam


btw u going to stroke it?

Great list Cam, thanks a lot. I'm not going to stroke it, because it's a 325i block, and not an e.

325i block? thats what machine work is for ;).. I am using a 2.5L block for my 2.8 Stroker

[Jand3rson]

Yeah, I'm not planning to go the stroker route, but thanks for clearing up the misconception I had.

Can anyone offer anymore info on a rebuild?

[Rigmaster]

Yeah, I'm not planning to go the stroker route, but thanks for clearing up the misconception I had.

Can anyone offer anymore info on a rebuild?

Be VERY careful if you decide to hot tank the block- there are some intermediate shaft bushings in there that can be destroyed by the caustic hot tank solution- and they are NOT available new anywhere.....FYI.

Bret.

[Jordan]

intermediate shaft bushings in there that can be destroyed by the caustic hot tank solution- and they are NOT available new anywhere.....FYI.

You can still buy them at any dealer... however... they are only offered with a new block attached to them.

[chrisd]

Be VERY careful if you decide to hot tank the block- there are some intermediate shaft bushings in there that can be destroyed by the caustic hot tank solution- and they are NOT available new anywhere.....FYI.

What are they made of? Just curious.

[Jon325i]

You can still buy them at any dealer... however... they are only offered with a new block attached to them.

Them must be some expensive bearings :shock:

Jon

[Spaz]

intermediate shaft bushings in there that can be destroyed by the caustic hot tank solution- and they are NOT available new anywhere.....FYI.

You can still buy them at any dealer... however... they are only offered with a new block attached to them.

They are basicly the same as cam bearings for a in block cam, such as a chev small block and what not. I'm pretty much sure machine shops will be able to macth them. I'll check out a couple of my friends shops and see what they can do, and maybe i cna get an anwser for this.

[BahnE30]

EDITED for Josh....

[E30/M30]

Valve guides ?

[Jand3rson]

here's a question for you guys that know something about the M20 how long do you figure it would take to replace rod and main bearing with the engine still in the car and does the crank have to come out to do this???
car has 370,xxxkm's on it and i don't want to end up with a boat anchor the rest of the motor is tight dosn't burn or leak a drop of oil so it's not time for a rebuild yet..

I don't mean to be rude, but please start another thread if you have a separate question.

[Digitalwave]

Josh, I think it'd be pretty stupid if you opened up the bottom end and didn't do any upgrades. Engine ran fine right....? Why do a stock rebuild then? Just wait till the motor dies, then do some nice upgrades to it.