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

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...

By the way, I haven't done it on mine, either.

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