M52 crank machining

[ForcedFirebird]

Don't forget forged pistons usually require .003"-.004" (.0762-.1016mm) clearance for expansion, so they are slapping until warmed up. This is 5x that of a stock m20 piston. They will also be heavier.

The Mahle pistons are very high quality. I have abused them pretty decently, even in turbo builds and haven't had any more issue that with forgings. I have yet to break a ring land, but have burned/broke holes though them when losing a valve under boost :/

[digger]

I think I'm going with new 85mm pistons and 135mm rods. Better R/S ratio than 130mm and no 160k mile pistons. After all....this is supposed to be a project :)

Any reason to go IE/Mahle vs custom JE for $200 more? Also looks like schrick and dbilas cam is about the same price.. The head has new OEM springs: should I go with dbilas 284/284 or schrick 284/272? I trust schrick but do not know much about dbilas cam.

The mahle are coated for protection against galling during run in, and for lower friction. They also have a nicer design particularly the skirts so they should be a bit lighter and stiffer.

JE can do the OEM dome shape (if you use the right dealer) but can’t do equivalent skirts as the Mahle with 4032 alloy, they don’t have the forgings for it. They give you the full skirt when you order a 4032 alloy. This in itself is not a big deal but the direction the industry is heading more and more is a non full skirt so there are advantages with this.

If you order 2618 JE can do the FSR skirt but it costs more anyway, especially if you get their skirt coating. The different alloy that comes with FSR skirt is better suited for FI or race applications and less ideal for a street engine that you want to cover a lot of miles and do lots of cold starts like something that gets driven multiple times a week experiences.

The rings from Mahle will probably be better, if I was to order a set of rings for a set of JE id be looking for total seal conventional sets not the standard JE ones that come with it, this will also cost more….

The advantage of the JE is they are a true custom piston as opposed to an off the shelf design, this means you could spec them in larger bore like 86mm, or for even bigger crank, higher CR, deeper pockets for big overlap cams for negligible extra cost. This might not be an advantage for you since you are using a specific crank and for a mild build, and the Mahle are basically ideally matched for this exact build anyway.

The head has new OEM springs: should I go with dbilas 284/284 or schrick 284/272? I trust schrick but do not know much about dbilas cam.

i know a guy who used dbilas 276, works well and quality seems on par with schrick

[zaq123]

I think I'm going with new 85mm pistons and 135mm rods. Better R/S ratio than 130mm and no 160k mile pistons. After all....this is supposed to be a project :)

Any reason to go IE/Mahle vs custom JE for $200 more? Also looks like schrick and dbilas cam is about the same price.. The head has new OEM springs: should I go with dbilas 284/284 or schrick 284/272? I trust schrick but do not know much about dbilas cam.

[ForcedFirebird]

A good 84mm OE set and good block will also be fine

Yup. As I said earlier, the extremely thigh OEM tolerance of the m20 has proven to me to hold for a long time. I would just have the machinist measure before doing anything.

[digger]

Thanks for your take on it, sounds like a pretty solid logic. I've seen +.5 pistons and was considering them as a replacement for my possibly tired 160k pistons. All in all...do you think extra 0.5mm (85mm total with IE/Mahle), deeper valve pockets (no interference with the larger crank) and an opportunity to leave pistons as is ( no notching etc) is worth extra $600? ..... $600 looks like $0 cam + a head gasket.... Hmm My biggest concern is ...in order to leave the crank alone, I have to mess with the pistons and that $600 margin can shrink to $400-300-200 very quick.

A good 84mm OE set and good block will also be fine

[zaq123]

I wouldn't turn the crank, I have always stayed away from under sizing them - specially on a 2.8, IMO when stroking an m20, you are creating a horrible R/S ratio and don't need any more of a failure point. I have always just had the journals polished, and scrap the ones that need a .010" under - I wouldn't even consider a .025" under.

The m52 crank does not need a lot of meat removed with the flat bottom short skirt pistons. The two center throws are larger than the rest. They will need about 5-6mm (guessing) and the outer ones will only need a 1-2mm. $450 to cut and balance the crank isn't overly expensive if you don't have it ground. I have actually notched the piston skirts just enough to clear the throws and left the m52 crank full circle, so that's an option too (this was with Mahle +.5mm stock replacement pistons)

BMW has extremely tight piston to wall clearances with a 83.98mm piston and 84mm bore (.01mm per side ~.0004", 4 tenths of a thousand of an inch - 1/10 the thickness of human hair). I have rarely have seen a decently kept m20 go out of round, and usually show sign of almost no wear. If you can see the cross hatches still, you will probably get away with a deglaze, we tend to go over size more for the added compression and small bump in displacement. Have your machinist measure to confirm.

Since you already have the crank, $450 for them to prep it up, spend $600 on +5mm OEM pistons, have the rotating assy balanced (~$250 here locally), and whatever your bore/hone is going to cost ($250 here), and take .010" off the block deck ($120 here). This will give you a very strong m20 for not a lot of money. I prefer to recondition the stock rods as they are seasoned and really strong already. If you use aftermarket rods, make sureyou have them checked for round and use the ARP 2000 stamped bolts. A lot of rod companies use the cheapest ARP, so you may need bolts and a big end resize even if they are aftermarket.

I wouldn't trust used stock springs unless they are tested for stiffness, never mind for a cam with extra lift. New OEM springs may be suitable for the 288, but if that's the minimum suggested, that's too close for my comfort.

Finally, shoot for a .045" head to piston clearance. The m20 really likes this number for some reason.

Thanks for your take on it, sounds like a pretty solid logic. I've seen +.5 pistons and was considering them as a replacement for my possibly tired 160k pistons. All in all...do you think extra 0.5mm (85mm total with IE/Mahle), deeper valve pockets (no interference with the larger crank) and an opportunity to leave pistons as is ( no notching etc) is worth extra $600? ..... $600 looks like $0 cam + a head gasket.... Hmm My biggest concern is ...in order to leave the crank alone, I have to mess with the pistons and that $600 margin can shrink to $400-300-200 very quick.

[digger]

in that case with MS and possibly ITB then yes that is the direction id be looking. , otherwise a 284/272 is still a good all round street cam but it gives up some topend due to the smaller exhaust duration (not much use bringing in air and fuel if you cant get it out efficiently)

i ran a catcams 298/285 as a daily driver inc A/C with OEM intake for a few years in bigger engine (bigger engine keeps things a little tamer compared to a smaller engine), and with standalone it was perfectly fine, drives better on ITB though ;).

[ForcedFirebird]

I wouldn't turn the crank, I have always stayed away from under sizing them - specially on a 2.8, IMO when stroking an m20, you are creating a horrible R/S ratio and don't need any more of a failure point. I have always just had the journals polished, and scrap the ones that need a .010" under - I wouldn't even consider a .025" under.

The m52 crank does not need a lot of meat removed with the flat bottom short skirt pistons. The two center throws are larger than the rest. They will need about 5-6mm (guessing) and the outer ones will only need a 1-2mm. $450 to cut and balance the crank isn't overly expensive if you don't have it ground. I have actually notched the piston skirts just enough to clear the throws and left the m52 crank full circle, so that's an option too (this was with Mahle +.5mm stock replacement pistons)

BMW has extremely tight piston to wall clearances with a 83.98mm piston and 84mm bore (.01mm per side ~.0004", 4 tenths of a thousand of an inch - 1/10 the thickness of human hair). I have rarely have seen a decently kept m20 go out of round, and usually show sign of almost no wear. If you can see the cross hatches still, you will probably get away with a deglaze, we tend to go over size more for the added compression and small bump in displacement. Have your machinist measure to confirm.

Since you already have the crank, $450 for them to prep it up, spend $600 on +5mm OEM pistons, have the rotating assy balanced (~$250 here locally), and whatever your bore/hone is going to cost ($250 here), and take .010" off the block deck ($120 here). This will give you a very strong m20 for not a lot of money. I prefer to recondition the stock rods as they are seasoned and really strong already. If you use aftermarket rods, make sureyou have them checked for round and use the ARP 2000 stamped bolts. A lot of rod companies use the cheapest ARP, so you may need bolts and a big end resize even if they are aftermarket.

I wouldn't trust used stock springs unless they are tested for stiffness, never mind for a cam with extra lift. New OEM springs may be suitable for the 288, but if that's the minimum suggested, that's too close for my comfort.

Finally, shoot for a .045" head to piston clearance. The m20 really likes this number for some reason.

[zaq123]

My plan is to use MS for this build with larger injectors (any recommendation on the size?). Will have to live with its stock intake and exhaust for a little while. Next mod on the list will be the exhaust and at some point ITB (hopefully). Any way to improve the oem intake? Should I look into into dbilas 284? I probably should pick up the adj. cam gear for the bigger cam and take care of head/block skim

it won't me my daily driver, just a weekend toy to have some fun in the twisties.

[digger]

With the b25 block the inference is less but it might be to do with the year of the block rather than if its b25 or b27. Basically any issues are pretty simple and straight forward. Things to check are:

- Crank counterweight webs to sides of block including intermediate shaft support bearings
- Bottom of cylinder bore and rod shoulder (24V OEM rods should be ok , some aftermarket rods cause more issue than others, the bigger the stroke the bigger the issue)
- Intermediate shaft and rod clearance (normally only an issue on big stroke crank e.g. 89.6mm)

Note to drop the crank in you need to orient it correctly (spin it on its axis)when lowering it down

The 288 isn’t a great cam with the OEM manifold as the 288 in a 2.8L wants to peak at an rpm much higher than the manifold is intended to be intune at. This is because the runners are a bit too long and restrictive so you end up being not fully utilizing the full benefit of the cam. With the RHD intake the 288 is a great balanced design.

Also if you’re still using motronic then the idle and drivability is a lot harder to get nice than with other systems once you introduce a fair bit of overlap.

It would be nice if schrick did a 284/284 instead of the 284/272…i think it would be a better option generally speaking (dbilas do a 284/284). however with OEM intake and exhaust and ECU a 272 might be better to live with on pure daily driver.

[zaq123]

My machinist uses one of those auto honing machines, no flex honing.

I think IE/M piston route is the way to go. Price sucks but I will know for sure that all bores are perfect and the short block is acceptable.

I don't really want to push it with 288 and oem springs plus my understanding 288 is too big of a cam for 2.8-2.9L. Maybe 284/272 max?

How bad is M52 big cw crank's interferance with m20b25 block? What areas in the block are know to need some clearancing? I've seen a sticky with the cut out for b27 block.. any info on b25? Would intermediate shaft be a problem?
Also anyone knows if M52 crank is still balanced when you take the sensor ring off?
That would be nice....if so, I will just need to do only last crank/flywheel+everything else balance and be done.

[redlightpete]

Another advantage of those I.E. pistons is that you can run a bigger cam that's more appropriate for a stroker, without having to cut deeper valve pockets in the pistons. I think the conventional wisdom is that you can run up to a 288 cam with stock valve springs.
Regarding the bore size, if all you do is flex-hone it, the bore shouldn't increase appreciably.

[digger]

Did you mean 2.8 suits the stock intake better?
So IE Mahle should work with M52 crank with no interference?

no, the bigger the crank will peak at lower rpm, typically mild engines around 5200-5500rpm, id expect closer to 6000rpm with a 2.8 it does vary depending on exact specs

those pistons should yes, that is what they are intended for

[zaq123]

A 3L it won’t breathe well at all especially with stock head, stock intake manifold............

The 3L probably suits the stock intake better which is good from 3500-5500rpm

Did you mean 2.8 suits the stock intake better?
So IE Mahle should work with M52 crank with no interference?

[digger]

Check out the cost of IE Mahle MS 85mm 10:1 forged pistons about $1200 iirc vs crank work, piston mods, etc

You’ll have to check Bentley for specs on bores etc and id trust advice on machinist for measurements and evaluation. Many people reuse pistons with nothing more than a hone if the bores are decent.

A 3L it won’t breathe well at all especially with stock head, stock intake manifold, and very mild cam which is fine if you just want more bottom end torque/midrange for a street engine. IMO a 3L and 2.8L will make about the same/similar peak hp numbers if there is nothing else different beside the crank but the 3L will make more power/torque below its peak and peak at lower rpm and fall over faster. The 3L probably suits the stock intake better which is good from 3500-5500rpm