BCS Oil Recommendations
At one time an automotive oil of the correct viscosity (SAE rating or "weight") was fine for British motorcycles, but times have changed.
Due to the ongoing reduction of most of the zinc and phosphorus from automotive motor oils in order to be compatible with catalytic converters, and the lower viscosity that is a characteristic of modern "gas saving" motor oils, Megacycle Cams has found that using the correct motor oil is a major factor in the longetivity of camshafts, and the associated cam followers.
Higher contact pressures encountered with high performance cams due to lobe design, usage of stronger springs, and high performance riding style can reduce borderline lubrication at these mating surfaces to insufficient lubrication, with the result that lack of these extreme pressure additives can create damaged components under certain circumstances.
Barb Dour of Megacycle Cams specifically warns against usage of current Castrol GTX and of Mobil 1, which in her experience have resulted in a disproportionate number of badly worn cams and followers, and says best results have been encountered using the following motorcycle specific lubricants with her cams. As a matter of interest, Megacycle may void warranty if other brands than those below are used and damage has been caused by lubrication failure:
*Joe Gibbs Racing Oil
*Brad-Penn # 1
*Valvoline Motorcycle Oil
Out of all the above, our personal choice would be Valvoline, which is a high quality petroleum oil, due to good availability, low cost, and the fact that higher seepage levels are a characteristic of using a synthetic oil in older design motorcycles, but further recommendations are invited, as it is possible there are other high zinc and phosphorus content oils we are not aware of that may also do an excellent job.
At British Cycle Supply Company, for post-war 4-stroke British motorcycle engines, we recommend motorcycle specific oil with no lower a viscosity rating than SAE 50 or 20/50 (unless freezing weather is expected to be encountered, in which case a reduction to 10/40 or 40 weight can be made if necessary,) with the understanding that these engines will never be driven under load until warmed up. For engines which share their engine oil with the primary drive (Triumph/BSA triples, 70on Triumph twins, and B50s) these multigrades are fine for both, but on other than the triples, do not use a monograde on these, to avoid dragging clutches. For those bikes with a separate oil supply in the primary case, we recommend a 10/30 or 20 weight motor oil with no special "friction reducing" additives for the primary drive, which can be reduced to a 5/30 or 10 weight oil under freezing conditions.
For all gearboxes we recommend Castrol "Hypoy C" 85/90 gear oil under all conditions, and for forks, we recommend the viscosity specified by the manufacturer be used, but in a motorcycle fork oil, not in a motor oil or Automatic Transmission Fluid.
Engine and primary drive oil changes should be every 1500 to 2000 miles or annually, whichever comes first, and gearboxes and forks annually unless extremely high mileages are covered, in which case fork and gearbox oil change intervals should be more frequent.
Incidentally, all dry sump motorcycles not fitted as original with a filter can benefit from installation of a full-flow oil filter (making sure it is not installed in the feed line from the oil tank so as not to be able to restrict flow if dirty.) There are specific oil filter kits available, using the Trident/Rocket 3 element, or the Norton filter - very adaptable and inexpensive.
And finally, compact and efficient oil coolers are readily available to adapt to machines ridden in hot weather, to help prevent premature oil breakdown due to oil temperatures exceeding 250 degrees, and these can be fitted with thermostatic or manual bypass valves to avoid condensation on cool days.
In closing, attention to the correct grade and type of cool, clean oil can help ensure a long lasting and reliable British bike.