Taken from the November 1972 issue of Cycle Magazine.
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pushrods so they stay put. This mechanical ballet is best done with two people, one to maneuver the head and the other to tend to the pushrods, which will take some fiddling to get them fully up into the head. If you do happen to bend a pushrod (check by rolling it on a flat surface and see if anything wobbles) make sure the replacement you buy is the right length, because some older model Norton pushrods look identical, but are just a little long. It goes without saying, if you have the engine out of the frame, you don't have to worry about any of this stuff.
Anyhow, after the head hassle is over, unbolt and pull off the barrels, making certain to stuff ceremonial rag into the crankcase to keep dirt and etc. out. Remove the piston pin clips with the circlip pliers if you've got them, or you can hamfist it like us and pull 'em out with a needlenose, if the tips are in good shape (9).
Now we come to important item #2:
To get rid of the old pistons, heat them up (remove the combustible cloth if you use a blow torch!) enough so that the wrist pins easily slide or press out (10). This point should be well below boiling, about 160° F (just too hot to hold). By no means hammer hard against the pins, because you can easily bend a rod doing that and wreck things for quite a while. If you must tap, support the rod on the other side as well.
After the old pistons are gone, you can unscrew the studs with pliers or vicegrips. Or, if you want to save the threads you can do it this way: run two nuts on to the stud and tighten together against each other; then turn the lower nut counter-clockwise and the stud will back out. With the old stuff out of the way, you are now ready for the second half.
Preparing the 810 Kit
Next you must adjust the ring gaps, which basically means filing down the ends so they don't overlap (12). The trick here is not to file too much off, and keep the ends square while you do it. We steadied the rings in a small vice and gently squeezed the ends together as we filed to put equal pressure on both end surfaces (13, 14). Measure the gap by placing the ring square in the bore and trying the feeler gauges until you get one that just slides in and out (15). If the bore is smaller at the bottom at the bottom of the liner, measure down there. Comparing the gap you've got with the Dunstall specs will tell you how much more to file.
After the rings are gapped, you can out them on the pistons (16). Fingers work fine here if you are careful. The bottom-most oil ring must be placed below its land (17), so the expander can be mounted. and then the lower ring placed in its slot in the expander. Make sure the notched edge of the compression ring goes downward (18). Check that the cam followers are free to move (19). Mount the new circlips in the inner side of the pistons, then put them in a warm oven (150 - 200° F), and your ready to start. Keep the Dunstall instructions and your poop sheet close at hand
Now put the cylinder over the pistons (followers go to the front) and slowly push the pistons through the compressors and up into the cylinder liners (22). This is one of those easier said than done operations, but be patient. Carefully squeeze the ring gaps closed with your fingernails as you slowly shove the pistons upwards and/or the barrel downwards. The bands on the ring compressor we used were a bit too wide, we'd
suggest you get narrower ones or cut them down. This is another time you'll be glad to have a friend to help with shoehorning the rings in, or at least to swear at.
Before you push the cylinder all the way down (after the pistons and rings are safely inside) install the new studs by our trusty two-nut method, explained before. Tighten two nuts together on a stud and run it in until it bottoms. then turn the bottom nut clockwise to loosen both nuts and run them off separately (23). Now you can shove the cylinder assembly home, and tighten it down diagonally from the inside. We know you're hot to get the head on, but before you do, trickle some oil down the pushrod tunnels (24), drop the rear head stud into its hole (25), place the head gasket on, and screw the other studs into the head a la Dunstall Info.
In replacing the head you will encounter the difficulty experienced in its removal, except in the reverse order. once you get the head and it's recessed pushrods over the cylinder, you'll have to tilt it back and very slightly to one side to coax #1 and 3 pushrods to drop into their holes, and then to the other side to accommodate the #2 and #4 (26). Before you sock the head down, check that all the p-rods ends are happily seated in their rockerarm ends and cam follower tops. Also, with the large pliers, you'll have to screw the rear stud up into the head (27). Try to hold it up high on the neck so the end threads don't get too buggered up. Then run in the various head bolts and nuts and torque them down to the Dunstall specs if you've got the equipment. Otherwise tighten them diagonally from the outside (see diagram in the Commando manual). The nut on the aforementioned rear head stud will probably require a box ender, and some of the others will too, depending on the casting.
Once the head is on you can button the rest up, remembering to set the valve clearances .002-inch tighter than before. And keep in mind that after about 50 miles you'll want to go through and tighten or torque everything all over again. Especially those exhaust ring clamps!
In summary, the result (29) worth the extra time and money? The 60 extra cc and upped compression ratio (30) did increase torque for around town driving; but they won't really be felt the way they should unless you open up the head with bigger carbs, ports, etc., the way the old master Dunstall does. If you plan to do that in the future it's a worthwhile investment. The lightweight followers will give the camshaft an easier life also. And don't forget the new alloy cylinder weighs 10 pounds less (31), will probably dissipate heat better, and last but uppermost (for we motorcyclists are a pretty vain lot after all) those spooky sandblast fins look great!