Quote:
Originally Posted by SpecialEdition_F87
Hmm, SPC happens when the bolt backs out enough over time that the bolt backs out and spins. Here’s a solution that doesn’t void your warranty or cost tons of money
With every oil change tq the crank bolt to spec.
Bingo! Problems solved just tighten the bolt my friends it’s honestly that easy
If you don’t wanna do that get the single large key crank hub precision dynamic offers. The 4 keyed if not drilled properly will fail. Precision has fixed quite a few already fixed crank hubs with the 4 keys and utilized their own with no failures
The problem with the 4 keyed failing is improper installation. If the drill isn’t perfect 100% straight your basically gonna fail and it’s only a matter of time.
Precision dynamics will mushroom inside the crank case allowing them to not have a perfectly drilled hole but will fit perfectly while other companies your relying on installation perfection and that’s not something to put your hopes on
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It is not only just the bolt backing out over time, but in most cases the inertia from everything driven off of the crank hub exerting a counter clockwise torque during rpm increases (down shifts, heavy acceleration) over a short period of time (so expecially down shifts and kick down on dcts) that acts like an impact driver which over time can cause the friction disk to break loose. So it is not just the bolt loosening.
No do not touch that bolt under any circumstances without the proper timing lock tools, because you can do more harm than good. Also that crank hub bolt is a torque to yield bolt which is stretched once yielded. This has a few implications:
1) The BMW specified torque is not technically accurate because once it is yielded the torque values can increase a bit, so even if you were to torque it to the pre yielded values it might not be enough and it will seem tight when it could have loosened a bit. However if the bolt is still above the pre yielded torque spec it should be fine, but this is to say that it is pointless to keep checking that torque spec because you could end up doing more harm than good.
2) If it ever loosens enough to allow for more torque at the pre-yielded torque spec you cannot keep retorquing a stretched bolt because it will snap off. A torque to yield bolt is meant to be torqued and yielded
ONCE so it is a terrible idea to keep touching it because you will weaken the bolt and cause it to fail.
Not to be rude, but do not touch the crank bolt that is the worse idea ever... BMW even states in their TIS not to touch that bolt without timing tools in place. Sure going in a tightening clock wise direction would not have a huge probability to cause timing to slip, but it is a bad idea to touch that bolt in general.
I have a few things to say about the precision dynamics hub:
1) There is literally nothing I could find about this hub on the forums, so I am skeptical to even use this item because of the lack of user feed back and testing data.
2) The way you have to drill the crank snout looks really sketchy and it also means there is no way back from this (in the even this hub is not good). Because after you drill this hub the key'ing method leaves a weird lop sided shape on the crank so you cannot go with an alternate solution like the SPLOCK or a stock hub because the missing material will cause an imbalance unlike a pinned hub which is symmetrical. Next you will not be able to switch over to the a pinned hub because of how much material this thing takes out, so a pinned designed won't work. This literally will cost you a new crank shaft if it goes wrong.
3) The design does look strong, but again the way the key is drilled looks difficult and if not drilled exactly to shape there will be areas of high stress due to low contact patch between the weird key shape and the hub snout. So this could be worse than a circular pin not better.
But if your shop cannot drill a perfectly straight hole with the alignment tools provided for a pinned hub then you probably shouldn't let you do this install because you are literally alerting your crank shaft.
Overall if you want to solve the loosening bolt issue get a CBC, if you want to get a crank hub solution I would personally wait out the precision dynamics option untill there is more testing, and go with a 4 pinned hub which is tried trued and proven, or get the VTT SPLOCK which is also pretty tested (rev.2 with the straight splines hasn't seen any failures yet iirc) and the easiest to install. Personally I think the best option is to have a hybrid design of splines (which are cut by a tool (and deeper than the VTT splines) to match the crank hub and not cut by the crank hub itself) and pins. Because splines are designed to handle torque so it is the best option if done right, and the pins would be for added safety just incase the crank material fails (which it shouldn't because it is insanely tough forged material) and just to really make it the best possible solution.