M90 Bottom end tear down

[browntown]

So I realized I tore down the bottom end, and forgot to post. My m90 is the 93.35mm flat top piston variety (L Block). Anywho here is my ridiculously overbuilt piston and cap organizer:


Fast forward to a completely torn down bottom end with suprisingly good looking bearing surfaces, no cylinder ridge to ream, and a bunch of parts.

When I get back from my work trip next week, I'll be looking for a local machinist that knows what he's doing. Thanks to all for the input.

On to the pics:







Not sure if this was necessary, but kept track anyways:


The end product


Came back in to see a completely disinterested family of animals and thirteen year old:

[Doughnut]

Very organized, thanks for sharing!

[slammin.e28]

I <3 m90.

[LJ851]

M90s are sweet, i am building one also. Pistons are soft so the rings tend to beat up on the ring grooves and wear them out. Make sure your machinist checks that.

If you have replace pistons Paul Burke makes some REALLY nice ones for a fair price. Add in an American 3.5 crank for a 3.6 stroker...

[browntown]

^ head is likely going to paul burke. I've talked to him at length and the guy will make you a camshaft out of solid billet too. Cost control and project creep become issues. Thanks for the heads up about the ring grooves. This was a low mileage motor (120k) and looks to be in good shape, but you never know till things are mic'd. Deves rings seem to be the only commercially available rings of any worth for these motors, and hopefully I don't need to go oversize or custom. $1000 on pistons isn't in the budget. A fella from AZ that just built one of these wen't oversize and JE pistons. His motor build became very expensive.

[kronus]

M90s are sweet, i am building one also. Pistons are soft so the rings tend to beat up on the ring grooves and wear them out. Make sure your machinist checks that.

If you have replace pistons Paul Burke makes some REALLY nice ones for a fair price. Add in an American 3.5 crank for a 3.6 stroker...

a B35 crank? Any issues with valve clearance with stock M90 pistons, or do you need custom pistons to get this to work?

Also, do you have any idea about cams? I've heard that a B35 cam will go in an M90 head and do "good things" but nothing more than that...

(I also have an M90 that's tired and needs a rebuild)

[LJ851]

a B35 crank? Any issues with valve clearance with stock M90 pistons, or do you need custom pistons to get this to work?

Also, do you have any idea about cams? I've heard that a B35 cam will go in an M90 head and do "good things" but nothing more than that...

(I also have an M90 that's tired and needs a rebuild)

The quick and dirty stroker is M90 block, rods, pistons and B35 crank and head. The pistons protrude past the deck but will still clear the head and ends up with 10 or 10.5 to 1 comp.

jb325is on this forum has this although he is running a 290 cam i think.

M90 heads are basically B34 heads, early ones are exactly the same and late ones have bigger intake ports but not as big as B35.

[LJ851]

^ head is likely going to paul burke. I've talked to him at length and the guy will make you a camshaft out of solid billet too. Cost control and project creep become issues.

Haha, so true. The same thing happened when i talked to Paul, i was immediately trying to justify another grand as we talked. OK, maybe 2.

Looking forward to seeing your build.

[kronus]

rad. 288 is optimal cam for that? Any idea on the total power results?

[VinniE30]

Why are you guys talking about using a B35 crank (for a 86mm stroke) on a M90? The M90 is relatively rare, doing this takes away from why it's sought after.

You can get the the same end result with boring out a M30B35 to the ~93mm bore of the M90. This is better IMO because you're not using a more expensive and more uncommon M90 to make it have the stroke of a M30B35; and also because you're starting out with a newer design engine all together. I believe the M30B35 has had some improvements since the M90 was designed. Correct me if i'm wrong but the M30B35 head flows better and has the newer design coolant ports.

TL;DR: Why do this with an M90 when you can do the same thing with the M30B35?

[kronus]

cause a. we have these blocks b. they will never be rare and collectible PRECISELY because the B35 is better

I haven't seen a single person specifically seek out a M90.

[Brian D]

You don't hang out at early model forums then. (mye28, first fives, big coupe) They are prized because of the free revving nature afforded by the short stroke.

[browntown]

Well I bought the car specifically for the m90. It's a better engine than the b35 me thinks. Besides the bore, the block is just like every other m30. I plan on keeping the original crank, rods, pistons, and cam (assuming everything mic's out correctly).

That being said I will modernize it a lil with:
- megasquirt w/ map & wasted spark (already have the distributor block off plate)
- just got a set of b35 exhaust manifolds back from the ceramic coater, and they're nice
- Have a b35 intake that will have a milos overbored throttlebody on the flipside.
- Screw on oil filter housing (milos again)
- Dual valve springs and head work probably by burke if I can afford it and he has the time
- adjustable cam gear (burke)
- g265

No a/c and no p/s with e32 smaller starter and bigger alternator. Also l/w 533i single mass flywheel and m5 clutch kit.

That's all I can think of in the pile of parts for now. A lot depends on what is in spec when the machinist measures everything.

[CorvallisBMW]

sub'd for m30 awesomenss :)

[Doughnut]

Why are you guys talking about using a B35 crank (for a 86mm stroke) on a M90? The M90 is relatively rare, doing this takes away from why it's sought after.

You can get the the same end result with boring out a M30B35 to the ~93mm bore of the M90. This is better IMO because you're not using a more expensive and more uncommon M90 to make it have the stroke of a M30B35; and also because you're starting out with a newer design engine all together. I believe the M30B35 has had some improvements since the M90 was designed. Correct me if i'm wrong but the M30B35 head flows better and has the newer design coolant ports.

TL;DR: Why do this with an M90 when you can do the same thing with the M30B35?

I kinda agree, m30 > m90.