Monograde or multigrade oil?

A bit of a yawn but wondering whether any other series 1 owners use multigrade oils in their injuns rather than the monograde SAE20, SAE30, SAE40 recommended in the WS and operation manual. It does say multigrade oils are recommended for injuns in good order as long as they match the SAE grades recommended. A mineral 15w40 should be ideal maybe?

or 20w50 any apart from the really thin would be okay unless engines like new

always used 20/50 (Duckhams) in the series when I had them , never had any issues , as james says dont go for thinner stuff .

Since posting I've been nerding it up in the workshop manual to get a better idea about bearing clearances and oil pressure readings. Clearance wise they are much tighter than you would imagine, similar to a ford 2.0 zetec engine so the recommended SAE20,30/10w30 is right for a new engine. This one has some wear though so will use the 15w40 mineral oil with a decent amount ZDDP in the formulation.

Millers oils contain a good level of ZDDP which is why I use them. I use their 20/50 classic though

Yeah Millers are a quality outfit. You don't want too much ZDDP, about 1200ppm seems to be the general thumbs up. Over about 1400ppm and it starts to have negative effects and over about 2000ppm it starts to attack the grain boundaries in the steel!

I'm going to do what i did with my Austin A35 and go by the pressure gauge and make sure the readings match the readings in the WS manual. On a S1 you should have about 25PSi on idle at full operating temp(min 20PSi) and a full operating temp oil pressure reading of between 55psi and 65 psi at 30mph in top gear.

If the readings are outside of that then the oil is too thick or thin. Too much pressure means not enough flow (oil too thick), which increases wear and too little pressure means too much flow (oil too thin/bearings worn) which does the same with sometimes a loss in oil supply as the oil pump can't keep up!

Mineral/semi synthetic oil seems to be the better option for sporadic use engines as well as it clings to the engine better than most synthetics do which reduces corrosion.

sorry about the brain dump lol

I use Millers in the V8 for that reason, zinc content helps slow the wear

I think you may be over egging the pudding ,lubrication technology has moved on in leaps and bounds since these engines were designed . The only real concern re what you use in them is that its not too thin , so it leaks out everywhere. A half decent mineral or semi syn multigrade will give better protection than the original spec oils were ever capable of . I used 20/50 in the various rover engines , some that worked hard and never had any probs over extended mileage . I do believe in using the best where it will justify , My 110 runs Redline in all the transmission components, for a number of years due to the harsh environment it has been in . My 90 on the otherhand just uses run of the mill lubricants , as its usage doesnt justify more . JMHO

I hear what you are saying, but getting the right viscosity is important for engine life. One thing to note is modern oils have had a lot of the EP additives removed to protect catalytic converters and particle filters so a lot of classic car owners are experiencing excessive cam wear when using them in historic engines.

The recommended viscosity is the right one as far as I can tell, originally SAE30 but with the development of multi-grade oils was updated to 10w30, same operating temp viscosity but just gets around the engine much faster when cold.

If it was a fully rebuilt engine I'd be using 10w30 mineral oil but it's got some wear on it now so will use an old spec 15w40.