In order to help people outside the UK who are working with British vehicle documentation, Richard Notton (Southampton UK) provides this information about British lubricants, their US equivalents, and a lot of generally useful wisdom.
British volume units are based on the Imperial Gallon which is not the same size as the US gallon. Here is the conversion information for British, US, and metric measures.
1 cu cm [cm3]
1 cu decimetre [dm3]
1 cu metre [m3]
1 litre [l]
1 hectolitre [hl]
1 cu inch [in3]
1 cu foot [ft3]
1 fluid ounce [fl oz]
1 pint [pt]
20 fl oz
1 gallon [gal]
1 fluid ounce
1.0408 UK fl oz
1 pint (16 fl oz)
0.8327 UK pt
0.8327 UK gal
British Army lubricant identification
OEP - Oil Extreme Pressure
OMD - Oil Mineral Detergent
OM - Oil Mineral
XG - Grease
PX - Additive
AL - Antifreeze
For example, the Ferret will call for OMD 110 for the engine and gearbox. This is a high detergent SAE 30 (MIL 2104). Later manuals may refer to OMD 75 which is a first generation 10W/30 and not a bit like current multigrade oil. The Specialist Engines Division of Rolls-Royce, who made the B60 (B=engine type; 6=cylinders; 0=3.5" bore [1=3.75" bore]) in the Ferret, provided this advice:
"We designed, developed, tested and approved the B range engines on SAE 30* to MIL 2104, but its your engine sir so you can put in it what you like."
* For atmospheric operating temps of 23ºF - 89ºF, above that SAE 50.
Incidentally, only the B81 engines have fully hard exhaust valves and seats; all others will need some lead replacement additive to keep things happy. Mil service schedules call for the replacement of exhaust valves at 20K miles, B81s excepted.
Further research with the technical departments of the major multi-national oil companies gave the general answer that straight 30 is advisable owing to the intended high oil consumption (relatively to todays car engines) where a multi-grade produces a small amount of very abrasive ash that quickly wears piston rings. For any gearbox application they advised that straight oils were more mechanically robust and would not advise the use of a multigrade. Its interesting to note that many current production big diesels are specified for SAE 30 only even now.
Some 15 imp gallons of 90EP alone is needed for a full change of the GO lubed bits in the Stalwart: 5 imp gallons in the engine (B81), 2 1/2 gallons in the gearbox and 1 gallon in the twin air filters alone. The cheaper, single use of OMD110/SAE 30 became attractive. I personally use Silkolene Ashford 30 which is qualified to MIL 2104D and about 1/3 the cost of a multigrade. The Fuchs Lubricants Company has a huge reputation amongst the car/motorcycle racing people. Silkolene is available in the US at Silkolene Shop and other dealers.
OEP 220 is EP90 hypoid gear oil, EP80W/90 is quite acceptable.
XG 279 is a calcium based grease.
OX 8 is brake fluid. Often these 50's/60's vehicles use hydraulic oil OM 13 in brake/clutch/steering/winch etc., this is a near equivalent of any ISO 15 hydraulic oil, the official stuff being the red aircraft hydraulic oil and not cheap, BP Bartram HV 15 is the commercial direct equivalent. (Re-mortgage the house first.)
OX 320 is occasionally called up as an additive to the reduction hub oil, this is colloidal graphite in suspension and does little or nothing except make the oil very black, its prime use is gun recoil slides.
Air Filters and Oil Filters
The Ferret Vokes (195 ft³/min) oil bath air filter is very good at its intended purpose and the result of a very expensive research exercise post WW II with the desperate experiences of the North African desert. It can be readily cleaned in the field and re-filled, and is capable of retaining a huge amount of particulates before becoming choked. In "domestic" service you probably only need to service it once! In the bigger B range engine applications two are used.
The "bat-wing" felt oil filter can be replaced with a (UK) Crosland #432 paper element, which I know are available there, however. . . . . . . . .
The B Range engines are designed for high volume oil flow with the relief valve set to 30 psi, felt filters on the face of it have a poor spec for filtration at typically 25 micron against a high flow rate, whereas a paper element is 12 micron at the worst but needs a substantially greater area to achieve the flow. The felt is proportionally very thick though and filters better than the void size spec would suggest as its a bit like trying to hit a golf ball through a forest, plenty of space between the trees but one of them eventually gets in the way.
The felt filters are readily obtainable here ex-mil either as the element or very cheaply as a complete unit already fitted into a new, unused housing assembly:
Marcus Glenn The Acorns Baulk Road Bisbrooke Uppingham Rutland LE15 9EH UK