Swing arm spindle quandary (2011)

So, my 1974(1975) Norton, (I'll get to that in a min) has a swing arm parts puzzle. The mk3 has felt oil wicks and felt disc and the bush boss is engineered to accept a "top hat" style bushing vs a straight bush and no permanent lube system with the felt things. Also, the Mk3 has two welch plugs that have to be drilled and tapped to remove, (which I had to do) So far so good?
Seems that when I took it apart, I had all the parts of a mk3 swing arm spindle, yet I have a 1974 1/2 Norton, (no rear disc, no els start, etc.) The PO was the original owner and I doubt he had the swing arm bosses milled to accept mk3 bush, etc. (* Old Britts will do this for a price)

Now my question is can my bike which was actually made in 1975, yet has every trait of a pre-1975 have the fixings of a 1975 mk3 swing arm components?

My 1975 (74?)


mk 3 exploded diagram
http://www.oldbritts.com/1975_g16.html

mk 2A exploded diagram
http://www.oldbritts.com/1973_g14.html

Mk 3 spindle


my spindle with no "cotter pin" flat spots, (mk2A style) but with felt oil wick!


Old Britts swing arm boss photo mk2A vs mk3.


my swing arm boss




Actual title


My bits, sans one welch plug and felt oil wick:

Are You Complaining ? .

I've seen this before on '74s. I didn't realize they still used the earlier spindle though. I think the current Andover spindles have both the tapped hole for the earlier style and the flats for the MKIII.

Interesting. But, I always look at the engine number on a lot of these bikes to get the true idea of what year they are. My '72 is titled as a '71, which was fine, because I could get a historical plate one year earlier. My '69 Trident is titled as a '70. But, back to your swingarm. Could the bike have been produced when they were ready for the MKIIA improvements, had the new MKIII swingarm, but had to use up a few of the old style spindles? Hail interchangibility! It's what's kept a lot of these bikes on the road.

From what I see I believe you have a Mk2A. The bike was built in 1974 (but not titled until 1975?). It does not have electric start from what I see.

The Mk2A used a short spindle like the Mk3, but it was anchored by a single 1/4 inch bolt and not the cotter pins of the Mk3. The Mk2A used the short bushes, felts and welch plugs. The swingarm is the standard 850, drum brake model. No original swingarm spindle had both central fixing bolt and machined way for the cotters. That was introduced on replacement spindles so they could be used in either Mk2A or Mk3 and eliminate the need to stock two separate short types.

By the way, none of the Commandos had "straight" bushes. They all are "tophat". The Mk2A and M3 are simply shorter to allow the use of the felts and welch plugs. Also the explosion from the Old Britts page is from the 1974 parts book for a Mk2, not a Mk2A.

I also have a "late" 74 MK2a. It has the spindle, welsh plugs etc... as a '75.
Seems that close to the model year transition they used up their inventory of MK2 parts?
My s.n. is 316656 and the ID plate says 6/74 manufacture.

Talked with Old Britts last March when I got my bike and discovered this, they said to just use '75 bits for repair/replace/rebuilding.

JD

Reviving this thread to ask about the swing arm and spindle of the Mk2a. If I understand the information correctly, both the swing arm and the spindle are unique to the Mk2a, as the spindle is short but drilled at centerpoint, and the swing arm would also have been milled deeper to accept the Welch plugs. Do I have that right?

I have a mk2, not 2a and it is 4/74 manufactured. It has the mk3 style spindle/bushes/wicks/plugs but held by the single bolt not the cotters.

Jdub said:

Reviving this thread to ask about the swing arm and spindle of the Mk2a. If I understand the information correctly, both the swing arm and the spindle are unique to the Mk2a, as the spindle is short but drilled at centerpoint, and the swing arm would also have been milled deeper to accept the Welch plugs. Do I have that right?

Click to expand...

I think it comes down to which month your Mk2a was built, my Dec73 Mk2a has the same set up as my 71 750 as far as the bushes, spindle and sealing components.

Jdub said:

Reviving this thread to ask about the swing arm and spindle of the Mk2a. If I understand the information correctly, both the swing arm and the spindle are unique to the Mk2a, as the spindle is short but drilled at centerpoint, and the swing arm would also have been milled deeper to accept the Welch plugs. Do I have that right?

Click to expand...

Yes. Late Mk2 and Mk2A so check if yours has the removable caps or welch plugs. The current replacement 'short' Mk3 06-4699 spindle has the central hole as well as the cotter flats so also fits the later Mk2/2A.