Alan G.

I bought pretty much all my rebuild parts from Don at EBS. The prices are competitive, and the service and advise was real good. I rebuilt at 93.5 K miles. I just had the crank checked out and polished. My rods needed some work to bring the bottom ends back to spec. I went with OEM bearings, and ARP Rod Bolts.

By the time you add in seals, gasket sets, chain rails, chains ect... it sure adds up quickly.

evoderby

It depends, here's the theory:

The nitrating layer on cranks typically has a surface depth of between 0.01" - 0.03" or 0.25 - 0.75mm.

This means that based on the minimum depth of .25mm (and thus staying on the safe side) you can resize journal diameter with .50mm before breaking through the nitrated layer.

Accordingly, using +.25mm bearings should be fine since you're only grinding away .125mm from the crank surface. Re-nitrating runs the risk of the crank getting bent in the process.

What it means in real life:

When grinding a crank the machine shop will very much notice when breaking through the hardened layer. I'd think in all these years people like Colin, Geoffrey and Steve will have a good insight into the Porsche nitrating depth and what's considered safe for a typical engine configuration (mild street vs. full race).

In short....I'd check with them since knowledge is the best form of insurance;-)

Mark Brook

Here's a photo of No6 conrod............

race911

I've stayed out of the nitriding discussion because basically all of my experience dates from the up-to-3.2L engines. (Isn't it wonderful the 3.6s are so robust, and I've got a decade plus of pounding on them mercilessly without having to do more than change oil and the occasional valve adjustment on the 964s?)

However...........back in the olden days: the first engine I did circa 1981 was to repair my 2.0 wannabe S. That had a "T" cast crank. Was told to junk that. By everyone from Jerry Woods on down. (I get that there ARE a couple of reasons why it would be desirable for a race engine, but I was 18 and trying to get the car running again.) Back it went in, for cost reasons. A few months later an "everything but the case included" '69S engine popped up from a guy just back from the 24 Hours of Daytona and he was needing another engine case. Oh, bad crank, too. Again, Porsche and non-Porsche experts told me to get a std/std crank.

As I got into my own shop in the mid-'80s, occasionally I'd see a 2.0-2.7 with bottom end damage. Now, we didn't have the internet obviously, but a quick phone call to those much more experienced than me in So Cal or Nor Cal kept me thinking the same way--get a std/std crank. Remember, it was $2-300 for a good used one.

Then came the era of basically having a crank graveyard. I'd moved back to go to law school, and a mini "fix dead 2.7 engines" business pretty much grew from nothing. I was doing an engine about every other week, buying all the 2.7 cores I could find. Recommendation still was the same--don't grind cranks. But they were still cheap.

Now? Where's the technology and cost to properly repair one? Have no idea because I haven't needed to address the issue. The faux RS actually got a 964 crank after some sort of failure with the previous owner. Could the original 993 crank have been saved? No idea. But it wasn't.

What I do know is that after all the time and effort to go into one of these at retail shop prices, the current price of a good std/std unit probably isn't a deal breaker.

Mark Brook

The shop that removed 0.25mm from my crank have told me today that in their experience there in no benefit from re-nitriding my crank as they have taken such a small amount off and the original treatment sinks deeper into the surface. Also, they add, that re-nitriding of cranks has been proven to sometimes have adverse effects on the crank resulting in distortion............

Seems like a bit of a minefield to me.......

J richard

The issue with cutting a crank is the white layer isn't a solid thickness, the treatment is progressively porous as you cut into it. You can cut it and it will most likely be fine for the street, but remember that part of the nitriding process is surface hardness, but the other aspect is stress relief to minimize surface fissures and potential cracking. You can understand why Porsche wants you to junk it.

Like Ken unless it was something really rare and hard to find I'd pick a used crank over a regrind every time. And yea you need a new rod. Balancing the whole set isn't a big deal just start with one in the same weight group.

evoderby

I have no idea what a factory new crank costs but I imagine it to cost several thousands. If a good used std/std crank is at hand for little money of course it makes sense to use this (have it crack tested, polished and cleaned with new plugs fitted).

BTW love the Radical in your avatar, here's one doing 6.48 @ the Nurburgring:

Mark Brook

I'm told you can either buy a new 964 crank for £4000ish, or buy a GT3 crank which is the same duration etc for less than £1000. Anyone heard of that??????

evoderby

I think the gt3 crank needs different/custom rods and a different pulley/ damper. Given the price difference you've mentioned against a standard 964 crank you could add a set of forged pistons into the equation at almost no 'extra' money....8000rpm bottom end sir? ;-)

race911

$1200-1500 over here, for what I've heard of in recent memory. (Friend was searching for one pretty hard earlier this year for his stock-baced PRC GTL class racer being built.)

As far as the Radical, that was pretty much a stunt by the factory. Vergers drove it from the factory there to "prove" it was a street car. Oh, and it's an SR8. Kind of like comparing my old RSA racer to a 964RSR....... Can't even imagine driving one with a raised ride height and treaded tires.

race911

Price above is for a good used std/std 964 crank, in case that wasn't clear.

darth

It's been my experience that a good used std/std crank can be had for anywhere from $1000.00 to $1500.00 which isn't too bad, but on closer examination, the journals usually measure at the lower limit of the std range. I look at this wear in the same manner one looks at a used tire close to the wear bars. I figure if Porsche sells 1st and 2nd undersized bearings and the shop manual describes the process of hardening, then it's probably acceptable to grind the crank and unless you're plan on entering the 24 hours of Lemans you can save the hardening charge. Be prepared to pay a premium for undersized bearings though, whether original Porsche or OEM and with the quality issues between the two, one may as well go original Porsche. Either way expect to pay somwhere around $2000.00 if you buy a used crank and replace with OEM bearings or grind the one you have, incur the minimal machining charges and replace with original Porsche berings. A third alternative is a factory rebuild I've seen on Ebay for $1200.00 plus core.

J richard

$1200? Motor Miester?

Good point about the oversize bearings, forgot about that one, they can set you back in both cost and time! More than makes up for the difference in getting a good crank...

Mark Brook

It seems the only place to source over-size bearings is from Porsche at £16.38 each plus 20% VAT, so £236 all in. EBS quoted me $312 or $26 each, so no really difference after import duty and tax.

Mark Brook

I'm trying to order the con rod bolts direct from ARP. they've asked me what size the thread is...... Does anyone know the exact dimensions please???

Cheers,

Mark.