Twin rockers

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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mdt-son
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Posts: 373
Joined: Wed Feb 01, 2012 1:22 pm
Location: Vestland NORWAY

Twin rockers

Post by mdt-son »

Hi

I am having a problem with a rocker intended for my restoration project ('64 G12CSR). As no new rockers are available as far as I know, I bought a used rocker off eBay which has indentation marks at the valve tip end.
Does anyone know the material used by AMC to cast the rockers? Is it cast steel or nodular cast iron? If cast steel, it will be case hardened. If cast iron, it might be a chill casting, in which local hardness is obtained by chills in the mold.
Rockers made of cast steel will experience plasticity (this seems to be the case here) and may be repaired by hard weld, but they need to be heat treated afterwards- this requires knowledge of the alloy they are made of.

-Knut
mdt-son
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Posts: 373
Joined: Wed Feb 01, 2012 1:22 pm
Location: Vestland NORWAY

Re: Twin rockers

Post by mdt-son »

I had the idea to check the product announcement for the new twins (The Motorcycle, Nov 11, 1949). According to the article the rockers are made of forged steel with the integral tips being hardened (usually this means they are nitrided).
The wear pattern shows plastic deformation of the rocker arm tip in contact with the valve stem.

What this means is that rockers are salvageable by hard facing arc rod and grinding the tips to shape. If valve stem tips are stillited, the rocker tip hardness requirement is 50 RC. Do replacement valves provided by the club (e.g., 026041 or Alpha Bearings V205) have stillited stem tips? There is no information in the AMOC listing nor with Alpha Bearings. If someone has made the above exercise, please share your experience and procedure.

-Knut
CAB
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Posts: 116
Joined: Thu Jul 09, 2009 9:10 pm
Location: CORNWALL UK

Re: Twin rockers

Post by CAB »

Hello

I had my rockers built up and reground by Newman Cams.

Regards

CAB
mdt-son
Member
Posts: 373
Joined: Wed Feb 01, 2012 1:22 pm
Location: Vestland NORWAY

Re: Twin rockers

Post by mdt-son »

That's a good address, CAB. Thanks for sharing.

Did you specify an RC hardness, or have information from Newman as to which hardness of deposit they used? Have you inspected the rockers after some mileage and do they hold up well?

-Knut
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