M52 crank machining

[mikerob97]

nice thread - if anyone reading is interested, I have an extra crank spacer and a set of eta 130mm connecting rods available for a 2.8 liter stroker build that I never used. PM me if interested.

[digger]

mine is just one half that, 47 thou. I guess I should grind it?

i would just to be sure, the counterweights in all honesty wont grow that much but the crank can also float axially close to 0.2mm, given its a 30 sec job to grind that area with a die grinder, its not really worth risking

[ForcedFirebird]

mine is just one half that, 47 thou. I guess I should grind it?

Rods can stretch .040+ (why you want piston to head clearance) - would be difficult to measure crankshaft wobble, but I would personally go close to .100" as possible to be safe...

[zaq123]

0.080-0.100" is more than enough.

mine is just one half that, 47 thou. I guess I should grind it?

[digger]

0.080-0.100" is more than enough.

[zaq123]

Update for this post.

will not be touching/cutting the crank and going with 135 rods and IE Mile pistons.

M52 crank clears my block nicely. They only area where it comes close is the oil return. Not my pic but the crank clears with about 1.2mm clearance there. Should I still grind the block? What # would you recommend as far as crank to block clearance goes?






Andrew's pic. My M52 crank actually clears there with the above mentioned clearance

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.

[nando]

S52 rods are pretty light, strong and at least they used to be cheap.

[SkiFree]

I weighed a 130mm oem "e" rod once and it came out to something like 633g. Heavy little sucker.

[whitebulat22]

Some weights from my maybe accurate home scale-

Mahle MS pistons- 310 g, 96 g per pin
M52 rods- 540 g
IE forged rods- 467 g

The cost was high for the pistons but I don't regret it. The 135 mm rods are a huge benefit imo because they're also a lot lighter than the shorter eta rods. Then the pistons are basically genuine BMW without the normal markup.

I vote for the 284 cam personally because I'm not seeing any complaints about drivability or loping from anybody running these cams. But with stock intake manifold it will be peaking just over 6000 rpm so the choice isn't going to make or break the powerband. With ITBs I bet there would be a noticeable difference.

[nando]

ITBs weren't really a thing when I built this - running the stock IM.

[zaq123]

I don't know that the stock springs were ever considered suitable for the 288 - the 284/272, yes (if new!), but Schrick specifically states in their catalog that you need upgraded springs with the 288.

FWIW I put almost 100,000 miles on my 284/272 with new OEM springs and never had an issue.

Also in 10 years of my M20 stroker, I never had any piston slap or rattle or burned any oil (leaking is another issue lol). It has about 85,000 miles on it now. I ran clearances similar to what Digger posted above with the 4032 alloy MM pistons.

I think we are talking 284/284 with new springs.....
Do you run ITB on your strocker or stock intake?

[nando]

I don't know that the stock springs were ever considered suitable for the 288 - the 284/272, yes (if new!), but Schrick specifically states in their catalog that you need upgraded springs with the 288.

FWIW I put almost 100,000 miles on my 284/272 with new OEM springs and never had an issue.

Also in 10 years of my M20 stroker, I never had any piston slap or rattle or burned any oil (leaking is another issue lol). It has about 85,000 miles on it now. I ran clearances similar to what Digger posted above with the 4032 alloy MM pistons.

[digger]

284/284 should be pretty good IMO, 276 works well, i was very impressed how it performed, it wont have the same topend so its more of a torquey beast but its usually a tradeoff

[zaq123]

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 :/

FF, thank you for your crank seal spacer, got it today. Haven't tried to install it yet. Was it designed as an interfearance fit? Any tips on the installation?

I ordered 135mm rods today so I'm pretty much committed to the aftermarket pistons at this point.

Gents,

I think I'll go with DBilas cam.

Street car that will be used with the wide rpm range (not daily driver):
2.8L with pretty much stock head with new oem springs(except Supertech valves and HD rockers)
Megasquirt
Stock exhaust for now and stock intake (for a while)

What is the consensus on the cam: 276, 282/270, 284 ?

[digger]

its more clearance but 4032 alloy JE (SRP) "only" require (0.0020-0.0025") clearance for NA (same as what MM spec on the wiseco slugs they sell dependent on application e.g. street, rally, race, FI a) its the 2618 alloys are normally 0.0030-0.0035" or more for FI

For the IE Mahle MS its going to be much the same as the 4032 alloy because that is basically what it is from a thermal point of view, these are the kind of alloys almost all OEM use when they use forged slugs on mass production. OEM like to run them tight to keep emissions low during warmup and reduced noise as the more the piston rocks the worse it seals, at operating temp there isnt any practical difference worth worrying too much about. also you can ask for pin offset to make them run quieter, the mahle MS will have offset most likely.

the stock pistons can and are usually run tighter, they have metal bands brazed into them to help control expansion despite having similar silicon content and thermal expansion coefficient as the forged 4032 plus i gather more R&D was done during development to work out how the piston behaves in terms of temperature profile in the engine and adjusting the ovality and taper of the barrel to suit. Still The more likely you are to put heat into them the more clearance you should run to avoid scuffing. From memory OEM s50B32 euro cast slugs are quite loose 0.0014" or there abouts as they see much more heat than the average engine

so yes aftermarket forged pistons will be run looser when cold and warmup but its not a huge issue with the right alloy (high silicon) 4032 as its minimized somewhat,

As for weight (exc pin, rings, locks) stock are ~370-410g ish depending on version, forged should be around mid to low 300 grams depending on bore and comp height i dont have a set of pistons for a 2.8L to weigh, the light stuff (long stroke engine, stroker pistons) can be into the high 200's so forged should be alot lighter.

anyone technically minded interested in piston tech should read this, probably the best source of information you will find

https://www.fsb.unizg.hr/miv/MSUI/KonMot/KonMot_2014/Pistons%20and%20Engine%20Testing_(Mahle_GmbH)_Vieweg+Teubner-2012.pdf