dished pistons

can anyone identify a pair of 73mm pistons (2.86" and 2.87") shallow dish, valve pockets and stamped 24 282 LH A and 242 83 RH B. at the moment they reside in a 750 dunstall cylinder affixed to a 72 commando. atlas??? early commando? also a cylinder head with number 06-0380 cast into bottom of bottom fin and "C" stamped top center between valve covers. combat head i assume but i can't find 06-0380 in any of my parts books? thank-you, b

biggles said:

can anyone identify a pair of 73mm pistons (2.86" and 2.87") shallow dish, valve pockets and stamped 24 282 LH A and 242 83 RH B.

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It was the early 750 Atlas models that had the low comp. concave topped pistons*, and the part numbers are within the same sequence but pistons were generally sold as an assembly with rings, circlips and gudgeon pin, so were listed under different part numbers to bare pistons which may not have been available separately but would still have their own part numbers.

*(although they are shown drawn in at least one commonly published exploded diagram of an early Commando engine, presumably because the Commando diagram was an updated version of the old Atlas drawing?)

biggles said:

also a cylinder head with number 06-0380 cast into bottom of bottom fin and "C" stamped top center between valve covers. combat head i assume but i can't find 06-0380 in any of my parts books?

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"Casting" numbers are not generally the same as part numbers, as the casting number would only be used to identify the unmachined casting, so do not expect to find those numbers listed in parts books.

Your head:

"Below is the early 68-70 commando head casting number 06-0380. .These standard RH1 ports are 28.5mm or 1.12". The number and BIRCO are easily visible on the intake side as positives."

For moree information go to:

http://atlanticgreen.com/nhth.htm

I have one that I will eventualy clean up and restore for sale.

RS

L.A.B. AND RoadScholar: greetings and a tip of the hat! a new query. i have a 73mm set of stock cast iron cylinders. spigotted at the top. the spigot does not fit into the relief of the combustion chamber on the earlier discussed head.(which thanks to you direction turns out to be a 71/72 milled combat head).neither of my dunstall cylinders nor any of my 850 cylinders have this spigot. is this an atlas piece or did 750 commandos have spigotted cylinders? trying to put something together on this mongrel of a bike to ride to the G P. doubt that it will happen now but i still must find a solution. thanks very much.

I think the spigot-ed part will be from an Atlas. I rebuilt my Commando with Atlas jugs many years back and I had to mill the top flat on the jugs.

I think the spigot-ed part will be from an Atlas. I rebuilt my Commando with Atlas jugs many years back and I had to mill the top flat on the jugs.

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And you will need to drill and tap the bolt holes in that cylinder from 5/16 to 3/8-26.

I'd forgotten that part.

hi biggles,cookie and ron are correct,i believe there is one other difference between atlas and commando barrels and thats the deck height(ie the measurement between the base flange and top flange)90 thou springs to mind but im not 100% , i had a set of atlas barrels machined to the same spec as the commando ones some years ago