Norton 850 Mk 1 1974, Service Notes, Page: 16 / 48

any Norton, or any other proper motorcycle, you will have to write out 100 times, "This is the Twentieth
Century").
As well as salt water getting into stud threads, Gunk is another culprit; regular Gunk cleans all the oil and
grease away so eventually they'll get water in and seize, barrel studs being a prime example.
MAIN BEARINGS: There are, so far, only two types of bearing 1 would recommend anyone to use in any
Norton twin (5()D up anyway). "These bearings are both Superblend Roller Bearings-one from Ransome
and Marles, Norton No: 063906, and one from F.A.G., Norton No: 064118. Either should be used in 500-
750 engines; the factory reckon only to use the F.A.G. bearings in the 830s There will be some end float
with the double roller-bearing set up which previously was controlled by the ball-bearing in the timing
side-this should be between 10 and 30 thou (0.25-0.75mm), but don't worry if it's not, as long as there is
some float. The outer rings of the hearings are glued in at the factory by Loctite Bearing Fit, so there's no
reason why you shouldn't use it too, as long as you make sure that the rings are hard home before the
glue sets, not when you find you haven't got any end float! Only use bearings with one of the following
nos: NJ306E (E is very important, NJ306 is weaker) or 6 MRJA30. The 6 may be hand engraved on the
bearing. The timing side bearing need not be a particularly tight fit on the crank. Again don't use just any
roller bearings, these ones are barrelled to allow crankshaft whip. Another number is NJ306E MI,
(Harder.)
BREATHING: The pre 200,000 motors had a timed breather which was so small it wasn't really much
good. The 200,000 series had a right angle joint at the bottom rear of the crankcase, joined to the oil tank
by a bit of washing machine hose. This system was, if anything, worse than before----at high r.p.m., more
oil went up the breather than up the scavenge pipe. Don't be tempted to replace the rubbery hose pipe
with plastic on 200,000 series motors-I have seen a nylon reinforced pipe melted by the hot oil going up it!
The other oil differences on late 750s are the elimination of the sump filters, and the resiting of the oil
pick-up at the front of the sump. I will never know why the filter was eliminated but was put back on the
850.
The 830 breather is much better than both earlier systems, but really you need 830 cases to make it
work, so that you get good oil return from the sump and a filter, but you can get good results by fitting a
pipe of about 1/2 in bore into the back of the timing chamber where the magneto used to go (in the days
when Lucas ignition systems were guaranteed for two years, including points wear). The pipe should stick
through the case about ;in and slope downwards, so that oil running down the inside of the case doesn't
get carried up the pipe with the air going out. Oil runs down from the inlet valve as well as sloshing about
from the timing gear. How you fit the pipe is up to you; you can't just buy the bits and slap them in. It is
also necessary to drill holes in the timing side crankcase-try and get a look in an 830 timing cover and
copy the size and position and I don't recommend drilling the holes without dismantling the engine; no
Malcolm, put that brace and bit down immediately! See Diagram 4, page 12
Oil leaks from the rev. counter drive can he a problem; try using two O rings at the same time and try
grinding a scroll on the spindle so that it tends to screw the oil out again, but remember, steel and
aluminum needs lubrication, so if no oil gets up there it will seize up and wear out the gear cut on the
camshaft, so don't overdo the pressure on the O ring. The later 830 has a modified type with the O ring at
the outer end, and it's supposed to be both better and interchangeable as an assembly. Not so, L. Em.
Final consolation of the late 750 owners, without sump filters-there is a magnetic drain plug which has a
chance of catching any bits (if metal on the way to the pump-unless the metal is aluminums. brass or
bronze.
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