MKV rear sprocket and drum

[hoejmark]

Hi
I am about to rebuild a MK5 rear wheel, and the brake drum and sprocket seem a bit strange to me.
The sprocket is bolted on to a flange that is welded on to the brake drum, and the offset from the drum facing to the sprocket is 5,2 mm and to the flange it is 12 mm. The sprocket is 60T.
Can somebody tell me how much offset there should be from drum facing to the sprocket facing, and can I fit a new sprocket to the flange and get the correct position?
Please see attached photos.
Hoejmark

[hoejmark]

Hi again
The MK5 frame is taken into parts and primer coated, ready for the painter. Therefor it is not easy for me to assemble the frame, rear forks, hub and gearbox again to line up and measure out where to place a new sprocket on to the hub.
It seem to me, that the flange welded to the brake drum is not normal for a MK5 hub. Is this flange placed where the sprocket ought to be, or can I bolt a new sprocket on to the side of the flange?
Does anybody know the right measure where to place a new sprocket. My MK3Sports is no longer in the house, so I have no possibility to measure my self.
Regards from Hoejmark
 

[douglas1947]

Hi Sören,

it is 6mm from drun to sprocket.

Michael

[hoejmark]

Hi Michael
Thanks for your reply.
When i fit a new sprocket, it will leave 5 mm instead of the 6 mm you have measured. I think that will not be bad.

I am wondering why there is a flange on the MK5 brake drum to bolt on the sprocket, as far as I know, the sprocket should be welded on?
Is it a brake drum belonging to another Mark model? Does anybody know about this.

Soren

[eddie]

Hi Hoejmark,
     Road going post war machines had the sprockets welded to the drum. Sports machines such as the Comp and the Plus had bolt on sprockets so that the overall gear ratios could be easily altered for different venues. The bolt on sprockets stood on 6 legs (the same as the welded on sprockets) and the drum had 6 separate welded on lugs for their attachment. Even these drums differed depending on whether they were for a Plus or Comp - the Comp had the chain line moved out by 1/4" to clear the wider tyre! The continuous ring on your drum is not the standard fitment, but probably improves the braking by preventing the drum from flexing.

  Regards,
                Eddie.

[hoejmark]

Hi Eddie
Thanks for your informations.
I will then search for a 60T sprocket that can adapt for shrink on and bolt. Probably from Yamaha TZR.
Regards
Soren

[eddie]

Hi Soren,
               The welded on road bike sprockets were for 1/2" x 5/16" chain whereas the bolted on sports sprockets were for 5/8" x 1/4" chain. Here in the UK, most bearing stockists can supply both types as plain sprocket blanks at a reasonable price (they know them as 'Plate Wheels'). All you then need is an engineering firm to bore the centre to suit your brakedrum, and then drill the fixing holes.

  Regards,
               Eddie.

[hoejmark]

Thanks again Eddie.
I will try that.
Soren

[tck]

Sprockets unlimited good service

[Daren W Australia]

on ebay today
https://www.ebay.co.uk/itm/DOUGLAS-MARK-6-DRAGONFLY-REAR-WHEEL-SPROCKET-SOLID-CONDITION/222788888038?hash=item33df40a5e6:g:MAIAAOSwHYVaVH8A

[hoejmark]

Daren
Thanks.
This sprocket has 52 teeth, as far as I can count up, and I think that i need 60 teeth.
Does the Dragonfly have same chain size as Mark5?

Regards
Soren

[douglas1947]

Hi Sören,

my MK5 has also 60 teeth sprocket (original welded on) 1/2 x 5/16" chain.
I know there is a shop in Hamburg for chain + sprockets.
If you want I can find out the contact.

Michael

[hoejmark]

Michael
I should appreciate that.
Soren

[eddie]

Hi Soren,
               On Mark series machines, a 60 tooth brakedrum/sprocket was standard. A 64 tooth alternative was available for the Mark 3 Sports. Both of these were for the 1/2" x 5/16" chain.
               The only option for the Dragonfly was a 51 tooth brakedrum/sprocket assembly - Later Dragonflies (with the British Hub brakes) had a bolt on sprocket (again 51 tooth). Both of these were for the larger 5/8" x 1/4" chain.

  Regards,
                Eddie.

[hoejmark]

Thanks Eddie.