Crankshaft damage - advice needed.

[FOZ1A]

https://www.ebay.co.uk/itm/184610449385

Foz

[kev edwards]

Drill and tap to take the larger bolt, you won't need the woodruff key, then just lap the rotor on.

[sharpeyie]

Drill and tap to take the larger bolt, you won't need the woodruff key, then just lap the rotor on.

Any thoughts on why this wouldn’t work anyone? Is this a better option than trying to repair the keyway?

[baz]

you will be wasting your time if you just lap the rotor to the crank the problem is you just cannot get enough torque on the 8mm bolt that holds the rotor on ( 18ftlbs ) that's why the z1000 has a bigger bolt 10mm thread unless you repair the keyway it will just come loose again

How does a keyway keep something tight ?

[kev edwards]

Drill and tap to take the larger bolt, you won't need the woodruff key, then just lap the rotor on.

Any thoughts on why this wouldn’t work anyone? Is this a better option than trying to repair the keyway?

The later ones are done this way, the larger diameter thread allows for it to be done up tighter, when lapped in you may have to change the rubber damper washer behind to a thinner one or rub your existing one down a bit. Hopefully another member who is more familiar with this process will happen along and add more information.

[zed1015]

The maximum torque applied to the M8 bolt on its own isn't enough to prevent the rotor from spinning (even when lapped) especially on deceleration when the rotors inertia doesn't want to slow down as fast as the crank which then allows the rotor to rotate anticlockwise and simultaneously slackens off the retaining bolt.
The woodruff key is there to prevent this.
The later non key cranks use a bigger M10 and later an M12 bolt which do allow enough torque to be applied.
The M8 thread could be increased to M10 to fix the issue but the taper is hardened which is evident by the chip damage.
Some cranks are harder than others but you will most likely need a cobalt drill and tungsten carbide tap at least for the job as HSS won't be hard enough.
Once lapped . if the starter clutch gear is binding the dished damper can be lapped on a flat surface to reduce its thickness.

[z1bman]

you will be wasting your time if you just lap the rotor to the crank the problem is you just cannot get enough torque on the 8mm bolt that holds the rotor on ( 18ftlbs ) that's why the z1000 has a bigger bolt 10mm thread unless you repair the keyway it will just come loose again

How does a keyway keep something tight ?

it doesn't keep it tight it prevents it from turning

[Mr Bump]

There's quite a lot of surface area missing from that plus the surface is scored.

As it's for a good bike I'd try and find another crank if one can be found. They seem to be fairly indestructible (apart from the taper!) so they often turn up for sensible money, at least for later Zeds anyway. Maybe a later crank with a bigger bolt thread would be a good fix, though I'm not sure what would fit what.

If it was a dog or I was in a rush I'd try cleaning it up and using loctite 648 bearing retainer to secure it. It's bodgy but it'd quite likely stay there forever and never come off again, even when you want it to.

Olly

[z1bman]

personally i wouldn't bother i would go for the one padders has for sale

[ChrisB]

My crank has the M8 bolt and I had a problem with the rotor coming loose. Your damage may have been caused by running the bike after the rotor was loose allowing the woodruff to move and elongate it's slot, eventually failing. Mine sheared the key in two, luckily I caught it in time. Mine had also had a crash which probably caused the problem as the tapered end had a fairly large runout which I hadn't previously noticed. SEP in Kegworth straightened my crank (they have loads of experience with old Zeds and are local). It may be advisable to cut another key slot but I'd take advice on that from the more knowledgeable engineers to be found here, or show the photos to SEP.

[Swirl]

I personally would buy the one off Padders, job done

[sharpeyie]

Huge thanks to everyone for their input. I eventually waved the white flag and have replaced the crank. A several of you said; ‘job done.'