Norton 850 Mk 1 1974, Service Notes, Page: 45 / 48

OIL
Further note, and explanations to the notes on page 28. When the Norton twin cylinder engine came
about in 1949 we had monograde oils only, therefore the design took this into account. the oil lubricated
the parts and helped with the cooling, especially the cylinder head. The dirt from Combustion would
usually end up in the oil tank its sludge, to he re-circulated in varying degrees. Not a marvellous state to
he in. In winter we used an SAE 30 and in summer, 40.
In time the oil companies came up with "Multigrades' by adding viscosity improvers, i.e. we had a 20
grade oil at 0°C which has additives which stop it becoming thinner than a 50 grade at 100°F also we
have further additives such as detergents. The advantages here are not quite what they seem. The
detergents hold the dirt in suspension, i.e. it continues to circulate and do it's 'thing', the only real
advantage here is that at least most of he contaminants and rubbish come out with the next oil change.
The real advantage that can he gained is by fitting an oil filter, as on the Interstate- in 1973. This allows
some extension of oil change periods, but not too far because of the viscosity improvers. When these
break down after u few thousand miles we are left with a 20 grade base oil. not clever stuff. Not at 110 at
110 anyway. (° and mph, that is.)
Also as the multigrade is based for cars with a lower BHP litre ratios and water cooled motor,, the
temperatures are reasonable with the additives lasting up to 100°('• but air cooled. high BHP/litre engines
can easily generate 130°C in the oil tanks while big end-, can he 50oC higher What value our multigrade
now? Some of the additives are also highly volatile! Another point is high piston and ring speeds, these
tend to shear these additives also.
What can you do? Use a heavy duty monograde 30 in winter, 50 summer as page 28. fit an oil filter and
keep to regular oil changes, certainly don't lengthen the oil change periods. The camshaft apexes have
most pressure exerted on them and these are usually the first signs of trouble with oil, when premature
wear sets in outside the normal soft camshaft wear on especially the Mark lll. Finally a 20/50 or 15/50
multigrade is preferable to a cheap non-HD monograde (keep to 2,000 mile oil changes), also not
recommended is the Castrol 4 stroke Motor Cycle oil known as GP. This is a 10/40W especially for
Hondas, i.e. engine oil has to circulate around the clutch and they have electric starters and monetary
wise are more important than Nortons in the motor cycle world.
Most engines seem to survive on the multigrade despite the above, multigrade does more with regard to
durability and quick-warm-ups
Well it fills a spare!
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