‘ Our crank hub has the timing gear as part of the hub, rather than being a separate sprocket that can spin on the hub’
The S55 in the F8X generation M cars is a truly spectacular engine, primed to be modified and even more so with Hack’ s crank hub upgrades
‘ Our crank hub has the timing gear as part of the hub, rather than being a separate sprocket that can spin on the hub’
So if it’ s not the crank hub and its design, but the bolt, what’ s causing the bolt to come loose?‘ I don’ t entirely know,’ says Ben.‘ All I can put it down to is that shock loading from the gearbox, shock loading the bolt so it starts to release. I think they’ re probably fastened correctly at the factory.’
How to fix the fault in detail?
As the bolt loosening is the root cause of the problem, it needs to be addressed first.‘ We make a capture plate, which goes over the crank bolt and stops the bolt from being able to loosen over time,’ Ben explains.‘ It’ s fitted from the outside, so there’ s no need to remove rocker covers or open the engine at all.’ The fitment of the part is easy, but the entire job isn’ t.‘ There are so many cooling pipes, electric water pumps and covers in the way on that platform, other than it’ s a really straightforward 15 minutes of work once you’ re in there.
‘ We’ ve had cars running over 660hp, with just the capture plate and the original crank hub, which we didn’ t recommend, but that was faultless. In some ways, that proves it’ s more the bolt than anything.’
The capture plate may address the main issue, but it doesn’ t solve the problem entirely.‘ You’ re stopping it from getting any looser. That will stop an issue getting worse and in 90 % of cases it’ s good enough,’ says Ben.‘ But you don’ t know how tight that crank bolt is when you fit the capture plate.’ And you can’ t just retorque it before you fit the capture plate, as Ben explains.‘ It’ s a single-use bolt. The only way to know that it’ s tight would be to undo the bolt and start again with a new one, which would then allow the timing to slip during that process, and if you’ re going that far, you might as well do that whole lot.’
The‘ whole lot’ is an improved crank hub. Hack’ s solution is a one-piece, fully-splined version.‘ Our crank hub has the timing gear as part of the hub, rather than being a separate sprocket that can spin on the hub. The timing gear is totally secure, as it’ s part of the hub.’ It is also attached to the crank differently.‘ The hub has a spline on the front edge of it, so it cuts a shallow spine into the crank; it’ s essentially a press fit
and it’ s far more secure than the diamond washer setup as there’ s a mechanical lock that way.’
Some other solutions on the market include dowels on the hub, also single-piece items, and the crank has to be drilled with corresponding holes. Hack’ s splined solution is more elegant.‘ It can all be done in the car, it’ s relatively straightforward. Our“ booked time” is 14 hours for doing it.’
Cutting splines, no matter how shallow, into the crank doesn’ t suit everyone’ s ideology. But Ben is an advocate, and Hack has proof that it works.‘ It’ s a really nice solution, it does the job perfectly. There are a lot of theories about the splines being cut into the crank causing damage if you try to remove it. We had an M4 that made good power on the standard engine using our crank hub design. Then we rebuilt the engine with stronger internals and we reused the same crank and crank hub. It went on to do over 930hp with no issues whatsoever. None of the negative comments I’ ve seen about the splined solution I think are valid.’
It’ s not just big horsepower cars that need a new and improved crank hub. If a car has flagged up a timing fault, the timing chain will be removed from the engine anyway, so it would be worth replacing the crank hub.
How long will it last?
Like the bolt, the crank hub doesn’ t totally solve the problem on its own. For total peace of mind, you have to pair it with the capture plate.‘ Regardless of whichever crank hub design you have, there is the potential for the bolt to come loose, and that’ s going to cause some upset. Whenever we do a crank upgrade, we do the capture plate as well, as that stops the bolt coming loose.’
An upgraded one-piece crank hub held in place by a new torqued-correctly bolt that’ s being held by a capture plate is the S55’ s biggest issue solved. Including if you want to get more power from the twin-turbo straight six.‘ I don’ t know where the limit would be,’ says Ben.‘ When the capture plate is there, the bolt’ s not going to loosen over time, so in theory it’ s fixed for life. There are no negative effects over time any more.’
Summer 2026 The Engine Rebuilder 57