Re: Fahey Hub questions..... (archive)

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I sucessfully R&R'd the crank bolt on my E34 M5. You need a special tool to hold the crank steady against the frame rail (an arm-like thing that bolts to the hub and rest on the frame rail) so you can apply the torque to take the bolt off. I rented a 4 ft wrench from http://www.koalamotorsport.com. Around $100 and they make the job a cinch!

Putting the bolt back on was easy too. You get a setting torque and then two angles for the E34. I was told that the E34 had torques earlier, but now has angles (which I much prefer as they don't rely on thread condition to be accurate). They had the same angle-spec for the head bolts. MUCH BETTER!

With the right tools from KMS, this job is easy. Just takes time. But, you know you'll be more careful than a shop when you do it yourself.

The crankshaft end is keyed and threaded, a rather typical design. The hub is positioned on the crank with a woodruff key and a nut goes on top, torques to some 350+ ft-lb. This is fine for your typical 4-banger getting 150hp at 5500-6000 rpm, but on the M88 descendents it tended to work loose. The hub slopping around would tear up the key and keyway in the crank. Eventually it would all come loose and make a mess of the front of the engine.

The repair included crankshaft replacement, as once the keyway is damaged a hub can never again be properly mated. This is very expensive. In the E34 M5 this design was replaced, no nut, no key, an entirely different design.

So Frank Fahey (sometime BMW tuner and performance parts manufacturer) designed a specially hardened replacement crank hub that prevents the key from working loose - don't ask me how or why, I don't know the details. I believe that Fahey sells the part for $350. When you replace the timing set, you must remove the crank hub, so there's no additional labor charge involved in the installation of the Fahey hub.

I've heard that by the end of the #28 M5 run the OEM hub material had been altered to fix the problem, but have never seen proof. I've also heard that it's not an issue unless you expect to track the car or engage in other activities that extract maximum performance from the engine.

After 200,000+ it's unlikely the hub is going to go bad spontaneously. For cause (more performance driving than the car has ever seen before comes to mind). But still, any time the hub is R&R'd, there's a risk of it not going back on as well as it was on before. That 350+ ft-lb torque of the hub nut can be hard to do correctly, for example. So long as you are throwing a wad of cash at it anyway...

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