E30 Touring 3.0L M20 Stoker Build

[MuDuRkKiO]

( ͡⚆ ͜ʖ ͡⚆) ( ͡☉ ͜ʖ ͡☉) Finally some good fuckin food Sent from my LG-H932 using Tapatalk

[digger]

I have a 86mm stroke S50B30US crank with the same number.

Could be it’s the forging number that gets machined into a bunch of applications

[E30-325iS]

Seem like that's what it is.

[E30-TourZing]

that p/n seems to be a M51 diesel crank 82.8mm stroke

http://www.athousakis.gr/en/product/...-2242898-9144/

Well Digger, you gave me inspiration to double check my numbers with a tad more accuracy. Its adding up more towards the 83mm mark, and causing me to believe the crank the diesel crank like you were suggesting it was.

My question for all you great folks would be... even if its 1mm off the ideal build spec, should I use it?

Pro's
- Small counter weights
- Likely weighs less (no official facts to prove this yet), meaning lower rotational mass.
- Less machine work on block
- I already have it
- My next best option to get a M52B28 crank will cost me a few hundred dollars + time tearing into the motor

Cons
- The MM Sport kit I bought is set up for 84mm crank
- Lower compression
- Lower displacement
- The serious mental condition of 'it-aint-perfect-itous'


I am aware millimetres in engine building have the potential to be a big deal. Do you think it will make enough of a critical difference that I should consider moving into a true 84mm? Does it have the potential to take 10,20,30 HP, lb/ft of torque away from its potential?

Keep in mind, i'm looking for a super fun street car, not a track car.


Any opinions would be greatly appreciated as I plan to send the block to the dentist in the next week or two.


Thank you all for your time! I really appreciate this community!

[digger]

The shorter stroke won’t take anything meaningful away from hp most likely as that is dictated by the head, intake and exhaust for the most part. The stroke just affects where the rpm peak is and the shape of the power curve and as a result the torque changes slightly. It’s only like a 1.5% change not a big deal so maybe 5ftlb all else equal

Just need to be mindful that the piston will sit 0.6 mm (half the difference in stroke) down the hole so the block would need to be decked (or thinner MLS gasket) to compensate to achieve the correct squish. Having said that the MM pistons probably aren’t setup for squish like the OE style anyway so its more about making sure the compression does drop too low.

[AWDBOB]

Just get the right crank IMO, m52 cranks are CHEAP and are all over the place.

[E30-TourZing]

So I just triple checked and here are the official results... Before I was measuring from the top of the con-rod, but I decided to get my facts straight and just measure directly from the crank to the top of the block.

On the down stroke my measurement was a pretty accurate 223mm

On the upstroke, my tally was 139mm

The difference is 84mm if my math is correct.

This must mean that I have a euro OBD1 M52B28 crank?

Either way, I am pretty excited. Next step is to do the brass hammer test to ensure its a solid candidate. Do most of you folks get your crank tested at your machine shop? Or do you just conduct the same test and call it a day?

Jim Rowe also told me not to polish the crank. While I certainly trust his word with his experience, have other community members spiffed up the journals while at the machine shop?

Thank you for your input!

[digger]

the nominal dimensions should be

206.2+84/2-22.5 = 225.7
206.2-84/2-22.5 = 141.7

but the delta is the important part

does it have a machine step for the tooth wheel on number 6 counterweight?

[ForcedFirebird]

does it have a machine step for the tooth wheel on number 6 counterweight?

Euro spec b28's had the crank sensor in the front, like the early USDM cranks. Only know this because a local has a z3 coupe that was sold by BMW as a motorsport-only car (no title, BMW USA couldn't even decipher the VIN). It had an m52, but since it was imported, it used the Euro DME and harness. The crank sensor went bad and had to order it from Europe. Aslo, the Euro cranks have smaller counter weights, no need to turn them down and re-balance.

EDIT: Also it appears in post #10 that the pistons do in fact have the proper squish dome.

[betz]

It's really not hard to find a good 84mm crank. Mine was like <$100 shipped on eBay and similar price at any local auto dismantler. And also not that hard to turn down the counterweights from the US one to clear your pistons. I took mine to a run of the mill machine shop and they charged me like an hour including all of my 325i pistons skirts getting shaved and their weights matched. You're gonna regret not having the stroke and compression, and I would kill for those MM pistons, they're pretty much the best you can get. I would use what they were designed to be used with.

[ForcedFirebird]

It's really not hard to find a good 84mm crank. Mine was like <$100 shipped on eBay and similar price at any local auto dismantler. And also not that hard to turn down the counterweights from the US one to clear your pistons. I took mine to a run of the mill machine shop and they charged me like an hour including all of my 325i pistons skirts getting shaved and their weights matched. You're gonna regret not having the stroke and compression, and I would kill for those MM pistons, they're pretty much the best you can get. I would use what they were designed to be used with.

The OP is in Europe, they got a different crank as they stayed OBD1 for a little longer than the states did. Their crank does not need turning.

[digger]

Euro spec b28's had the crank sensor in the front, like the early USDM cranks. Only know this because a local has a z3 coupe that was sold by BMW as a motorsport-only car (no title, BMW USA couldn't even decipher the VIN). It had an m52, but since it was imported, it used the Euro DME and harness. The crank sensor went bad and had to order it from Europe. Aslo, the Euro cranks have smaller counter weights, no need to turn them down and re-balance.

EDIT: Also it appears in post #10 that the pistons do in fact have the proper squish dome.

yeah that's exactly that's why i mentioned it if it doesn't have it then its one of the OBD1 crank. He is in Canada so would be pretty rare? Europe and Oz its very common

i don't think the dome on those exactly matches the OE there is some kind of chamfer though. My Rally slugs were similar, the new rally lugs are like flat tops

[ForcedFirebird]

Oh Canada!....well a lot of grey market cars here in the states come from CAN as the have much looser import restrictions. Prior to the 25yr rule, the only "easy" way we could get tourings (as well as real e36m3's) was import from CAN. The only other way I know is when Military brings cars home, and immigrants are allowed to bring certain vehicles once brought up to US DOT standards.

[E30-TourZing]

Thank you everyone for your input!

The crank I have does not have any connecting points on the counter weights like OBD2 M52B28 cranks do.

I am intrigued about the numbers you have digger. I am fairly sure the ETA block I have has only put on roughly 60,000Km's, so I doubt the block has been decked. 2mm of difference it quite a big step. Rather puzzling. I am trying to be as accurate as I can be with two straight-edge rulers.

The smaller counter weights do assist me quite a bit. With a standard OBD2 M52B28 crank, the counter weights run into the auxiliary shaft. This is fixed by machining 8-thousands of an inch off. I am pleased I do not need to do that anymore.

While Canada does likely have more euro spec vehicles per capita vs the states, we still do not see many around here. To touch on 'Betz' comment, I have looked into all the BMW wreckers within a 1000 km's of where I live and no one has one available unless I purchase an entire motor. The cheapest option I could find was $500. Buying from the states has literally been eating my project funds like an obese child and cake. By the time I cover shipping, duty and the + 30% increase in the US dollar, it hardly makes it worth it to just buy one off ebay. This is why I am quite excited to officially find what I am looking for. Not only that, I feel like I have been thrown a bone considering its better setup for my application.

I also lucked out on my 86' ETA block. It has single lock tang main bearing caps which saves me from sending out my caps to M/M. Jim thought that was the only M20 block year to have this from the factory. I got this block completely by chance.



This is what the top of my piston looks like. There are big valve reliefs as you can see. Hopefully the block height issue as mentioned above will not impede this build. I have a metric mechanic improved coolant flow head gasket. I am not sure the thickness, but its certainly not as thin as MLS.



P1011349 by Jan Willem Wilderom, on Flickr

[digger]

I have a M52B28 OBD2 crank in a M20B25 on a stand. I can measure this weekend rather than do the maths.

What’s the deck height (top of block to crank c/l) on yours? Mine is like 206.2mm

Why do you want single tang? I thought there were less bearing options for those? My current engine is a single tanger B25 from 87 iirc.

The crank C/W won’t hit the actual intermediate shaft the connecting rod will. The big counterweight hits a bit of the block in a couple areas, near the block main web areas that bulge out a bit, one of which is near the intermediate shaft. It does this on b27 blocks but not b25. One of the sticky threads regarding the block has the pics

You will want to pay a bit of attention prior to final assembly with mocking up and seeing where the pistons comes at TDC to optimize the combustion chamber, CR etc. If you don’t have a selection of gasket thicknesses it needs to be in the deck height machining. also check the angle of the piston chamfer and see how it mates to the head