IDLER GEAR SPINDLE: The spindle for the idler gear (that's the one that is both sprocket and pinion) should be tight
in the cases. If not, dry the cases off thoroughly and warm with a blowlamp before refitting the spindle with a drop or
two of "Bearing fit" loctite If it has been turning and will push in cold, copper plate it to a thou or two of interference
and try again (Have about five thou plated on and rub dawn to the required size with worn-out emery. Nickel or chrome
are too hard to rub down like this and must be ground to size). The oil hole goes underneath with the slot in the outer
end horizontal.
This spindle has been slack on my 1970 motor for yonks to no ill effect. Makes cam chain tension a bit awkward
to get right though. Case cracked open about 3/16in and a dabble and tug with a bent bicycle spoke (the same
one 1 use for push rod aligning) usually gets the problem sorted.
CAMSHAFTS: The later camshafts are tuftrided –a process which gives hardness without losing toughness. It can be
recognized by an even brownish grey color all over the shaft. Many dealers may still have earlier shafts on which the
cams are bright and these are not so good. so if you are after a cam, shop around. Avoid the SS cam like the plague--it
is nothing but trouble in a road bike and is slower than the ordinary cam (which was, after all, the grind used for those
650 production wins at Thruxton -- you remember, in the good old days when Notions won races), It is a good plan to
ease the end of the cam where the sprocket fits, so that this too can be pulled off easily -the next time. Never hammer
the cam nut tight without a cutaway timing cover or all your work getting the idler spindle tight will he undone. Even
pressure is sufficient and will cause no trouble.
A box spanner is preferable here, as the nut is shallow and slightly recessed ; a ring will tend to slip.
The "SS" cam mentioned here is the Commando SS cam or double S as used in the Combat engine (Interstate) as
opposed to the Commando standard cam which stemmed from the 650 SS profile mentioned. Referred to as the
"SS" because of its origin. This standard cam profile is as used on tire Atlas as well, and is now reverted to for
the 850s.
CAM BUSHES: If you are unlucky enough to have a pair of cases with steel cam bushes (they are bronze faced. but
can be recognized by the X-shaped oil grooves in the bronze surface of the bush), you must use bronze faced thrust
washers each side of the timing side crankcase. Break off the tabs which locate the washers in the hole alongside the
bush or they will break off in use. They are exactly the right size to drop into the crankcase and pass up the oil return to
the oil pump, "is seizes the pump, stops the oil supply, and within a very few yards the evidence disappears through the
bottom of the crankcases. There is no sump filter on the 1972 crankcases, and these are the ones with the steel hushes.
Very clever,
Further if; the steel cam bushes with "X"' oil grooves. or scrolling - these may be used with a plain or scrolled
camshaft. On no account fit a plain camshaft in plain bushes. Plain bushes were fitted to early engines and are
now being used again.
PISTONS: Don't buy new pistons with a slot under the oil control ring. This slot was deleted to avoid the top coming
off the piston when the revs were kept up towards 7,000. Of course, the slotted pistons are OK for the man who never
goes over 5,000 rpm. The later type are identified as Combat Pistons in the parts list, but the only difference is this slot-
the compression height of combat (non slotted) and standard (slotted) pistons is identical. The higher ratio of the
Combat engine was achieved by planning 40 thou off the cylinder head.
Atlas pistons will fit straight into the 750 Commando giving the lower
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