Mystery (to me anyway) rocker box 45-2595

[jmatch]

Found this in a box of recent swap meet parts and can't figure out what bike it's from.  Clearly BSA pre-unit twin but I've never seen one like this. Any ideas?  Looks like it has an access port (threaded for cap) on the top to help align pushrods and rockers. And the inspection cover is "puffier" than the ones I'm used to and attaches differently too. Thanks for any suggestions. John in NC
 

[duTch]

 Probably Ariel (Huntmaster ?) - subject has come up before

[jmatch]

OK that was quick, looks like an Ariel part, forgot about that connection with BSA in the 50's.  I searched the site for Ariel and found pics of a modified BSA part that added the inspection port on top, mine is clearly Ariel with the different inspection cover fastening and the machined flat on top.  Thanks!

[TT John]

A lot of these were fitted by the lads, to make it easier to get the push rods in place, they were considered better than the BSA  rocker box for that reason.

[Swarfcut]

Yes, it is from a FH Ariel Huntmaster, which is basically a standard A10 internally, with  different  outer castings to disguise the engine's BSA origin. A clever bit of corporate badge engineering to save the development costs on another in house brand. The timing covers fool a lot of folks, looking like A10, but being just slightly different enough not to fit an A10 crankcase. The rocker box is well worth using, saves a lot of anguish settling those pushrods.

 Swarfy.