[veer90]

So I'm having trouble with the crank hub spinning and my car being out of time. This happened twice within the last 2 months. Car is currently in the shop getting inspected, as to whether the hub itself slipped or just the timing sprocket.

Some background as this isn't a common N54 issue: the timing sprocket is not keyed to the hub or crank on N54s, N55s, and S55s. If enough load is applied via the timing chain or serpentine belt, the hub or timing sprocket can be forced to spin in relation to the crankshaft. Realoem diagram for reference. #3 is a large torque-to-yield bolt requiring 76 ft-lb + 360 degrees.

I was wondering whether it's plausible to do a stud conversion on the crank snout? Replace the TTY bolt with a threaded stud and nut similar to wheel studs and head studs on built, high boost engines. The reason being because a stud does not experience rotational stresses, it can generate a higher clamping force than the equivalent bolt assuming the proper materials are used (i.e. not cheap ass hardware store stuff). Also, what are your thoughts on replacing the factory friction material with industrial strength locking washers?

Any input is appreciated. I'm also open to other REVERSIBLE solutions for locking down the timing sprocket / hub so it doesn't spin on me ever again. That means no welding the hub / gears onto the crankshaft. Thanks!

[LaxIan55]

I know TPG tuning in Pennsylvania has solved this issue for their shop M4, not sure if this is at all compatible with our n54s though.

[135Pats]

Originally Posted by LaxIan55

I know TPG tuning in Pennsylvania has solved this issue for their shop M4, not sure if this is at all compatible with our n54s though.

At least as of a few months ago, their key'd design did not work, and there were still failures at an alarming rate. Gintani produced a different hub which I believe works, but not sure if it's been mass produced.

Edit: Gintani hub failed on the Max PSI shop car. So much for the S55...But I digress.

[weehe126]

If it is anything like the S55, once it spins it will keep on spinning. Can't comment on your idea. But if it works might help s55 as well.

[veer90]

Right, both TPG and Gintani's solutions had problems. TPG's keyed sprocket cracked and Gintani's one piece hub had incorrect pitch between the teeth, so the chain would not seat perfectly on them.

I think the latest development is Gintani's new bolt, requiring something crazy like 300+ ft-lb of torque.

[veer90]

bump anyone have ideas or input? or know of a bmw master tech who I can contact?

[M-335]

Maybe 1 or 2 small tack welds on the bolt

[doctorjdb]

There was issues with tension on the crank gear moving and causing cam timing to move, as I remember this was a problem early on and they cam out with 2 thin washers that had a rough surface to allegedly help grip and keep the gear in place. I do not find any bulletins about it or the part listed today. I have not heard much mention of this issue anymore, until now.
I do know it is important to replace the crank bolt and cam bolts when removed, also the torque sequence is pretty critical with the angle torque needing to be adhered to.
I would also say if the hub has any marks on it's mounting flange, I would replace it also.

Hope that sheds some light on this for you,
Jeff

[JamesM3M5]

Are you revving the engine higher than 7000 RPM? Different clutch/flywheel, especially a single mass flywheel?

Single mass flywheel is necessary, I understand, but this causes massive problems with the crankshaft at very high power outputs and high engine speeds.

It is not the fault of the bolt, but the overall design of the nose of the crankshaft / hub / sprocket. The crankshaft suffers from torsional vibrations, which have to be damped by both the dual mass flywheel and the vibration damper at the front. If you remove the dual mass flywheel, the torsional vibration is too great to keep the hub and sprocket from slipping. Even the DCT flywheel is dual mass. Dual mass flywheels decouple the heavy back half of the flywheel and the entire mass of the clutch from the torsional vibrations in the crankshaft. Conversely, a single mass flywheel and clutch, unless they're really small diameter, lightweight components, exacerbate torsional vibrations of the crankshaft that manifest in the front crank hub and sprocket slipping, or other attachment methods to fail miserably.

The S38B38, S50B30/32, S54, S62, S65, S85, and probably other crankshafts employ 4 M12 bolts that hold the hub and sprocket to the nose of the crankshaft. This design requires a larger diameter sprocket than can be fit in the space. Example pic from the S54. Maybe it is possible to get new crankshafts made with such an attachment, maybe M10 bolts, and greater mass to withstand the severe torsional vibrations experienced with such incredible torque output, higher revs, and heavy as hell single mass flywheel/clutch assemblies.

[M-335]

Maybe this will help https://store.vacmotorsports.com/mob...n54-p3758.aspx