Plus service literature recommended the following oils. SAE numbers have been added where I was able to cross reference them from other sources (in parenthesis.).
Engine:
Mobiloil “D”___(SAE 50)
Castrol Grand Prix___(SAE 50)
Golden Shell
Essolube Racer
Gearbox:
Mobiloil “B.B.”
Castrol X.L.___(SAE 30)
Double Shell
Essolube 40
Front Forks:
Mobiloil Artic___(SAE 20)
Castrolite___(SAE 20)
Single Shell
Essolube 20
You were not expected to go racing your Plus in the winter, but from the 1948-1954 Mark Series handbook (published 1960) the following were recommended. And what is a Plus engine after all but an overwrought Mark? The SAE numbers were provided in the handbook, and in some cases (Energol, Essolube, and Shell X-100 series) formed part of the nomenclature.
Engine, Summer:
Mobiloil “D”___SAE 50
Castrol XXL___SAE 40
Energol SAE 40___SAE 40
Essolube SAE 50___SAE 50
Shell-X 100 SAE 50___SAE 50
Engine, Winter:
Mobiloil “A”___SAE 30
Castrol XL___SAE 30
Energol SAE 30___SAE 30
Essolube SAE 30___SAE 30
Shell-X 100 SAE 40___SAE 40
Gearbox:
Mobiloil “D”___SAE 50
Castrol Grand Prix___SAE 50
Energol SAE 50___SAE 50
Essolube SAE 50___SAE 50
Shell X-100 SAE 50___SAE 50
Front Forks:
Mobil Artic___SAE 20
Castrolite___SAE 20
Energol SAE 20___SAE 20
Essolube SAE 20___SAE 20
Shell X-100 SAE 20___SAE 20
One difference from the Plus Series lubrication specification seems to be the use of 30W (SAE weight) oil in the gearbox rather than 50W. The gearboxes are nearly identical except that the sleeve-gear bearing in the Plus box has a needle roller bearing fitted and in the Mark series it is a plain bronze bushing. However the use of thinner oil probably has more to do with reducing churning power loss than this bearing. The plain bronze bearing is more sensitive to oil deprivation compared to a roller bearing. So if 50W can get in there to do the job for the plain bearing, it would certainly be adequate for the needs of the roller bearing.
From an early T35 handbook (November 1947), the following was culled. Again, cross referenced weights are in parenthesis. I do not know for certain what the SAE ratings are for the others are, other than extrapolation from the above of engine summer- 50W and winter- 30W; transmission- 30W; front forks- 20W.
Engine, Summer:
Mobiloil D or BB
Castrol XXL___(SAE 50)
Motorine ‘C'
Essolube 50
Triple Shell
Engine, Winter:
Mobiloil A___(SAE 30)
Castrol XL___(SAE 30)
Motorine ‘AA’
Essolube 40
Double Shell
Gearbox:
Mobiloil D___(SAE 50)
Castrol “ST”
Motorine Amber A
Essolube Gear Lube Medium
Golden Shell
Front Forks:
Mobil Artic___(SAE 20)
Castrolite___(SAE 20)
Motorine E
Essolube 20
Single Shell
I have used automatic transmission oil in the front forks of my Mark 3 (about SAE 15), but frankly this is a bit thin and more damping would be desirable. Also it dribbles. The Plus front forks are similar construction except they have two-way damping.
And now for a few words about the use of modern oils in old motor cycles, first the great mono-grade verses multi-weight debate. Here in the USA it is possible (on the east coast anyway) to still get straight grade oils though the selection is dwindling. Pennzoil and Castrol brands are two that offer mono-grades in SAE 40, 50, and 60 weights that I have seen in the local Auto DIY centers and at automotive performance/speed shops. But what about multi-weights? Well the main theoretical objections are two. While 10-30W and 10-40W are quite common, 20-50W is harder to find (Castrol is the only brand I have seen with such in stores.) Second, multi-weight oils do not like being run through gear teeth and roller bearings as it chops up the polymer chains that enable the viscosity to thicken when the oil warms up. So in time you end up with all mono-grade at the low end of the viscosity range. However I have found that this is not such a problem as long before this point is reached the oil has either leaked out, been burnt down the exhaust pipe, or (should you be so lucky) lasted without replenishment to the next oil change. Indeed on my Mark 3 I use 20-50W, 10-40W, straight 50W, 30W or anything else that was handy, depending on exigencies. Obviously the thinner oils make more smoke than straight 50W, which still makes quite a bit of smoke on start up. And some have said unkindly even after it warms up.
The second great debate is the use of detergency oils in older engines without a modern, efficient oil filter. The purpose of detergency in the oil is to keep the wear debris and combustion byproduct contamination in circulation with the oil, till it gets trapped in the oil filter. In a system without an oil filter, this means the wear debris particles just continue to circulate around and around the engine. Back in the old days prior to oil filters and specifically detergent oils, the idea was any contaminants would settle out in the sump. Also the crankpins have a large internal void which acts as a centrifugal sludge trap. I am not sure just when detergent oil became common, though oil filters on cars long predated it. If you change the oil fairly frequently (or have to top up frequently due to losses!) then it probably does not matter if you use detergent oil. The engine gets a fresh oil supply long before the concentrations build up. However you should not switch over to detergent oil in an engine that has been run on non-detergent oil for a long time. The reason is the old engine will have years of accumulated sludge in the engine that has separated out. That is until the detergent disturbs it, and starts to lift it into circulation. If a chunk breaks loose and blocks an oil way it is the equivalent of stroke. At minimum a large amount of damaging wear debris and particles will get into all the bearings. So when putting an engine on a detergent diet make sure the engine is thoroughly flushed out. Better yet, do it after a total engine rebuild.
For grease, I found the following names from the post-war era: Mobilgrease No. 2, Castrolease CL, Energrease C3, Esso Grease (not much marketing effort?), Shell Retinax A, Shell Retinax RB, and my favorite Blemoline C. Ah yes, back when grease had proper names that you could be on personal terms with. Not some cold technology sounding ‘lithium molybdenum disulfide’. Trip that off your tongue around motor cycle friends and you sound desperate to impress.
-Doug
