mercury rear brake drum and rear brake plate.

The Mercury bikes were built at the same time as the fits Commandos. Many of engine and gearbox components were modified Commando chunks. Possibly the rear wheel was the same,  minus the rim off-set.

The 42 tooth drum sprocket suggests this may be a Commando item. 43 being found of the earlier Dominator twins. What are the threads on the sleeve nuts? They were 26tpi CEI on the early Dominators but 28tpi UNF on the Commando. The Commando sleeve nuts were also much longer and I think were painted Blue on the Mercury.

Check out the attachment.

Hi Denis,  I don't think there is any problem..  You should have one locating stud and two non locating studs . All the holes in the hub are designed to accept either type of stud and it does not matter which stud goes where. The locating is effected by the combination of the locating stud in any hole  and the axle.  Seems a bit odd when you are being extra carefull to assemble things correctly and can't match things up, its designed so to allow any idiot to get it right every time !!. Clever or what ?.

is in the pitch circle of the hub studs and sleeve nuts.  The 1955-7 'full width' rear hubs used the same sprocket / drum as the earlier iron hub.  The alloy 'full width' hub proved vulnerable to loose sleeve nuts, so when the 1957-on hub was introduced, the studs were on a larger pitch circle. 

Paul

Hi Denis , It does sound that you have a problem. It would help us to work out what it is if you could give some more background . Have these parts come from a running bike ?, Is it a collection of parts from a basket case?, Have you bought a drum from the internet (possibly our Indian friends) ?  There has been drums pattern type that were poorly machined and with bad studs that come loose etc. What I would not do is bore out the Hub hole as this is likely to be an orriginal part , just check the hole is not bruised. 

My understanding of the two level and one short collars was that this allowed the drum / hub to be wobbled a bit during dismantling. Thus helping to break any seal formed by oil or grease or corrosion crap between the two chunks.

The  original parts lists describes the studs as  2 non locating and one locating stud,  Allowing the locating stud a choice of 3 holes to find makes me think someone realised that finding  a matching dedicated hole for the locating stud on a dark wet Febuary  night  on the M1  ( me on the way to the Dragon Rally ) was too much to ask.  And it would have been.