rockers same for all twin models?

Chris_van_p

Joined
Jan 30, 2014
Messages
8
Finally, after years of ebay-ing found a downdraught true 500 SS head in fairly good shape but without any internals.
Valves, spindles etc are straight forward and I can sort that out.
Only one thing I'm not sure about is the rocker arms -> are all rockers arms ever used on 500 600 650 750 twins the same or had downdraught heads other valve angels and therefor other arms?
Hope you Norton-buffs cab help out.
 
Thats a straight parts book question, if no-one can answer off the top of their head.
(Didn't the rocker ratio change at some point ?).

The 1962 parts book, pre SS heads, says that all twins have
18249 Inlet rocker RHS
18250 Inlet Rocker LHS
18251 Exhaust Rocker RHS
18252 Exhaust Rocker LHS.

late 750 and all 850 Commandos are
062471 Inlet Rocker RHS
062473 Inlet Rocker LHS
062472 Exhaust Rocker RHS
062474 Exhaust Rocker LHS

You'd need to find part numbers/list for an SS head,
and compare.

I seem to recall Commando are different to dommie here,
but its been a long time...
 
An ex- Norton racer and engine builder friend tells me that Commando rockers are ratio'd, Atlas and other earlier twins are not. If this is correct, and it most likely is, then that is one of the small differences that account for the extra HP of the Commando vs Atlas.

Glen
 
Rohan said:
Thats a straight parts book question, if no-one can answer off the top of their head.
(Didn't the rocker ratio change at some point ?).

The 1962 parts book, pre SS heads, says that all twins have
18249 Inlet rocker RHS
18250 Inlet Rocker LHS
18251 Exhaust Rocker RHS
18252 Exhaust Rocker LHS.

late 750 and all 850 Commandos are
062471 Inlet Rocker RHS
062473 Inlet Rocker LHS
062472 Exhaust Rocker RHS
062474 Exhaust Rocker LHS


You'd need to find part numbers/list for an SS head,
and compare.

I seem to recall Commando are different to dommie here,
but its been a long time...
Click to expand...

66-68 parts book has:
25332 inlet rocker RHS
25330 inlet rocker LHS
25336 exhaust rocker RHS
25334exhaust rocker LHS
 
Chris_van_p said:
Finally, after years of ebay-ing found a downdraught true 500 SS head
Click to expand...


You lucky young man :D

In 15 years of looking I found one good, one not so good.
 
I am not sure on the SS head. The earlier heads like the 88 and 99 used a rocker that was about 3/16 inch wider on the spindle than the commando rockers. The extra is width toward the center of the head.
If your head is built for the wider rockers you can use the later Commando rockers if you use a spacer next to the spring washer.

As far as I know the ratios were the same. Jim
 
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