Hi Folks, I have just machined my 3.0 crank to first oversize 0.25mm, however on installing the clearance on the mains has come out over spec, so I have few questions to you folks who may have experience here.

I have a clearance of 3.5 thou with the factory spec being 1.1 to 2.75 thou (as per manual).
I also have just installed piston squirters so I am concerned that the slight over clearance and squirters may cause oil pressure problems?

I am been told that Porsche 944 cranks cant be machined and that anyone who does go undersize will experience problems...is there a problem with 944 cranks in this regard.

Related to that second point does anyone know what thickness the factory crank hardening goes too? I assume it is a nitriding process, as far as I can research the process seem to be around 10 - 30 thou deep - obviously first oversize at -0.25mm is pretty close to 10 thou, so is there an issue?

thanks
mike

 

ok a few questions back at ya why was it resized was it damaged ??
are you getting the 3.5 thou on the mains or the bigs ?
are you getting it all the way round or just up and down ??
did you torque ups the rods and girdle with no bearings and measure first ??
and the process on the crank is induction hardening and i think it is pretty deep as it's still pretty hard on one i have 30 tho under.
and tell me about your inlet manifold mike ?

 

oo i re read its the mains ok these ****ty engines flog out mains i mean the block itself they often need to be line bored .
if it is only showing oval up and down machinist can sometimes cheat by just skimminng say .0006" off the bottom of the block to hopefully give you a .0029 measurement vertically.
check what the out of round tollerence is in the manual this will help you and the machinist decide if it has to be line bored .

 

Adam, I'll recheck as they normally check the bearing top to bottom when measuring, interesting point you raise about maching will look into it.

The max wear clearance I think is over 7 thou, so I am well wihin that, I wonder if 3.5 thou is acceptable, would save me a whole heap of work if so?

rgds
mike

p.s manifold is on hold till I get the engine assembled.

 

well my manifold is also on hold as the ***** in woolangong who has it doesn't respond to me emails .
can you go see him with a jack handle .
I realy don't know about those mains although loose is fast i would be more concerned about this increased clearance resulting in reduced pressure fed to the big ends .
look into what is industie standard there will be so many tho per inch of journal somewhere in general motor talk forums

 

yeah the indistry standard seems to be one thou or close per inch of journal, so I am a thou over

 

Adam are you sure Porsche use induction hardening vs Nitriding on the 944?

 

well reasonably confident you can see the heat markings on near the journals and I had a bearing trashed on a crank i have and the journal was spotless.
I think i will end up nitriting mine in the end as the crank is realy pretty expensive I'd like to ensure it

 

yeah Adam, checked again, looks like your right there are signs of localised heating around the journals that suggest induction hardening, thats good news as the depth is much higher than Nitriding, heres an extract from a paper I found on hardening.

Most stock OEM steel crankshafts have been induction hardened. This is a low cost process in which the surface is heated by a high frequency alternating magnetic field that generates heat in the crank's surface quickly before being quenched. The depth of this hardening process is around .060 - .080. Because of uneven heating and cooling, this crankshaft hardening process creates stress within the crankshaft. While it is an ideal hardening process for stock applications, it is less then favorable for high performance racing applications.

Nitriding is a chemical hardening process in which the part is heated in a furnace, the oxygen is vacuumed out, and nitrogen is introduced which penetrates the entire surface. The depth of hardness is dependent upon the time the crankshaft is exposed to the gas. Typically, a nitrided crankshaft will have a hardness depth of about .010 - .030. Nitriding is a low heat process compared to Tuftriding, but it shares the advantage of avoiding the introduction of localized stress zones as in induction hardening.

 

so i wonder when they "stress relieve it " as they offer to do at the machine shop does that undermine the induction hardening process?