GROUP 3:- Timing cover, all therein and rocker feed
TIMING COVER: Not a part that's been messed about with much by the designer chappies. If you ever need a new
one don't forget the oilway plug on the feed to the pressure release valve and of course the two oil seals. The middle
seal (crankshaft) goes with die garter where you can 't see it, and has a circlip. The other one (camshaft points
protection) has the garter visible and relies on friction• holding it in place, so a smear of silicone RTV might reduce
the possibility of a weep into the points, (The garter is the spring thing that presses on the edge of the seal to make it
work.) While we're on the subject, later points oil seals are red and better but won't cope with engine breathing
which is all awry. The 850 has a breather where the mag used to be but you can't do this to a 750 without making
holes in the timing side crankcase. The oil normally drains through the main bearing, mainly (!) and if the crankcase
has to breathe the other way through the same place the oil level in the timing case rises until the points seal can't
cope. See section on Breathing.
If you have a persistent oil leak into the points and the seal is O.K. there are two other possible causes (at least).
There have been timing covers which were porous (how unusual, I hear you say) but-porous between the inside and
the points lead hole. This can be cared by enlarging the hole if necessary to 5/16in (0.3125in=7.938mm, say
8.00mm) and inserting a thin sleeve of your own manufacture, or of Norton manufacture if you can get one. Stick
the sleeve in with plastic gasket or the afore-mentioned sticky substance. The other cause is use of an incorrect (i.e.
Dominator) or spurious timing cover gasket, which does not include the hole for the points lead or hole for oil feed
to pumpfitting a Dommie gasket will empty the oil tank into the sump. You CANNOT FIT an early type, of timing
cover to the early Commando although it looks the same with the r/counter on the side. The proper Commando
gasket is thick -a bit thicker than the average cornflakes packet and they don't leak oil. The paper ones are spurious,
or Dominator or Atlas (early).
Timing cover screws; die one long screw goes in the deep hole nearest the pressure release, and the short ones go
where the little bulges stick out around the cover. The flat headed sort are early ones, Whitworth thread (1/4in x 20
tpi) : later bikes, 1972 on have domed heads, w identify the UNC threads (} x 20 tpi--well I never!). Proper names
for the heads are "cheese" and "fillster". A set of socket screws from your local friendly dealer, Wassel item, is well
worthwhile. Except that being nickel plated the inside of the hole goes rusty so smear them with grease. Stainless is
best but dearest.
POINTS COVER: The points plate types are many and various-the latest have two screws to lock the points gap and
two screws to position each set of points and are somewhat easier to ad just The contacts which had one big point
and one small point-presumably to reduce unsprung weight (the latest ones have bath points the same size again!)--
rapidly wear into one another and give erratic timing. They also demand a rather special type of feeler gauge not
available from Uncle Joseph. You should all by now be using the "new improved" type of auto advance unit
recognized by having the outer spring posts bent up from the backing plate rather than thin bits of metal spot-welded
on afterwards. They really are much better-the pity of it all is that they were not available years ago, say, when the
Jubilee was about. Don't be tempted to use any A.T.D. from a B.S.A, or Triumph even if it does advance the right
way, the range and the spring poundage (ounceage'?) may still be wrong. The B.S.A, A65L one works O.K. ft will
give 30' retard. not 24" though, great for tickovers. If you are a well built fellow don't heave too hard on the points
plate screws-especially the plate fixing screws themselves. Broken screws can be difficult to remove (they are 2BA
but you can drill and tap new holes a bit further round if you're careful. Next time try B.S.A_-Triumph clamping
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