How to lighten commando rocker arms

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tonybsa

tonybsa

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Starting to lighten my rockers for my race bike-as per the Jim Schmidt book. Has anybody got any suggestions on how to machine the outside of the spindle bosses true to the bores where the rocker spindles go through.
 
Can’t help with your question. But thought I’d share some inspiration...

How to lighten commando rocker arms
 
None. . . it's all done by eye and hand. BTW just make sure you remove equal amounts of metal from each pair of inlets and exhausts by weighing them.
 
I did mine by hand using the photos in the Dunstal tuning book got some accurate small scales and got the matched pairs weighing the same .Very rewarding and enjoyable job ,did mine about 14 years ago good luck
 
Are you referring to the face of the boss where it would be up against the thackery washer?
If so, have a piece turned to the size of the spindle with a shoulder on it. You can use magic marker on the shoulder. Insert it into the rocker and turn it up against the shoulder. This will leave the high spots marked. File just the marked spots down. Draw filing would be best, so as to not round the shoulder of the boss. Repete this until the surface is all marked.
I don't know the size of the spindle, but you may be able to find a bolt with a washer face to use if you cant turn a piece to size.
picclick.co.uk

PAUL DUNSTALL – NORTON MOTORCYCLES Tuning Manual c1970 • £49.99

PAUL DUNSTALL – NORTON MOTORCYCLES Tuning Manual c1970 - £49.99. FOR SALE! POOKS MOTOR BOOKS POOKS MOTOR BOOKS Click images to enlarge Description PAUL DUNSTALL – NORTON MOTORCYCLES Tuning Manual From Circa 1970 FORMAT: Stapled Manual, 32 Pages + Covers. LANGUAGES: English. ILLUSTRATIONS: Black...
picclick.co.uk picclick.co.uk
 
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Here's how Reg Pridmore did it back in the day.
$75 exchanged with your rockers. My catalog is undated, around 1980.
How to lighten commando rocker arms
 
With the rocker pivot on a sliding mandrel and mount adjustable die grinder or Dremel and ball stone. (for starters)

Once they are perfect the gain will be a shine. (lol)
 
franko said:
Are you referring to the face of the boss where it would be up against the thackery washer?
If so, have a piece turned to the size of the spindle with a shoulder on it. You can use magic marker on the shoulder. Insert it into the rocker and turn it up against the shoulder. This will leave the high spots marked. File just the marked spots down. Draw filing would be best, so as to not round the shoulder of the boss. Repete this until the surface is all marked.
I don't know the size of the spindle, but you may be able to find a bolt with a washer face to use if you cant turn a piece to size.
picclick.co.uk

PAUL DUNSTALL – NORTON MOTORCYCLES Tuning Manual c1970 • £49.99

PAUL DUNSTALL – NORTON MOTORCYCLES Tuning Manual c1970 - £49.99. FOR SALE! POOKS MOTOR BOOKS POOKS MOTOR BOOKS Click images to enlarge Description PAUL DUNSTALL – NORTON MOTORCYCLES Tuning Manual From Circa 1970 FORMAT: Stapled Manual, 32 Pages + Covers. LANGUAGES: English. ILLUSTRATIONS: Black...
picclick.co.uk picclick.co.uk
Click to expand...
No ,I can reface that part at work on a surface grinder.Its the outside diameter,that runs parrallel with the spindle.I have the dunstall tuning guide.
 
Bernhard said:
None. . . it's all done by eye and hand. BTW just make sure you remove equal amounts of metal from each pair of inlets and exhausts by weighing them.
Click to expand...
I would have thought end for end weights were more important than overall. The center is irrelevant as it is supported by the spindle, only the ends are reciprocating.
 
No doubt they were. It was Dunstall in his Norton tuning booklet who stated that the ex and inlet rockers should weight the same.
Just see the booklet.
 
Jim Comstock did mine. No idea how he did it, but as you can see he mainly did the ends and sides. This makes sense to me as that is where the most of the effective weight to be removed on a street bike is. Not much point in thinning out the fulcrum point, compared to the weight at the end of the fulcrum.

How to lighten commando rocker arms


How to lighten commando rocker arms
 
In the UK at least opinions about this have varied. Gus Kuhn was adament should be left alone, but I once saw a set in a shop in Bexleyheath that looked like paper knives. Cant rememember his name but he claimed to have done sets for Dunstall
 
oldmikew said:
In the UK at least opinions about this have varied. Gus Kuhn was adament should be left alone, but I once saw a set in a shop in Bexleyheath that looked like paper knives. Cant rememember his name but he claimed to have done sets for Dunstall
Click to expand...
A before and after dyno comparison, with no other changes, may never have been done, by anyone.
 
Fast Eddie said:
Watching Comnoz’ Spintron videos and the bizarre things that happen to the valve train at high rpm made me decide it’s a small price to pay for a little more peace of mind.
Click to expand...
I totally agree that if you are going to take your bike near or to redline it's going to help keep things in place. But for most I think it is just one more thing you can do for no good reason. I bet my bikes have never seen much above 6,000 if that. Go ahead and roast me now.
 
Conical or beehive springs seem to control better. Better ramps on the cams control bounce as well.

Mine is a higher than normal rpm motor, but not a race motor. I do get it up to the redline in spirited riding.

Like Nigel says, piece of mind. Especially when viewed as part of the total performance engine package.
 
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