5-30 fuly synthetic in BMC B series engine

Being synthetic is irrelevant, but it's way too thin. Even if it makes oil pressure, the engine will likely wreck itself in short order.

With any pushrod engine, you need to be sure the oil in use has suitable additives to keep camshaft etc wear to a minimum. The loading between cam and follower is much higher than on a modern multi-valve OHC design. And sadly, the best additives - ZDP based - aren't compatible with modern catalytic convertors. So the best oil is likely to be one made for your engine type. Or use an additive.

I asked a top man on rebuilding older Ferrari lumps which oil to use and he said to use magnetec, apparently synthetics also tend to leak more than dino lube

Apart from age, do B series engines and Ferrari engines have much in common? ;-)

Tim

I think the age and original grade are pretty important likenesses, particularly with regard to the oil leakage side. Correct spec oils are still available for the MGB, so for the cost of a gallon a year what would be the point in trying to reduce the number of oils in stock? If I ever actually get my MGB (rotting away due to an inheritance dispute) I will use the right oil in it :)

Maybe but I was thinking more about relative BHP per litre. I would imagine that a Ferrari engine might be more demanding with regard to its oil than a B series one.

Tim

Don't be silly. Oil pressure is of little importance. Except when it drops drastically due to engine wear. The important bit is oil circulation - not some magic figure on a gauge.

Oh - the range of oils specified over the life of the B series engine changed dramatically also.

If the oil will take more bhp from the ferrari then it should definitely cope with the B, both engine types are similar in that they use plain bearings, which is one of the most important areas to consider.

Power and specific power have little to do with it.

2 things not found in Ferrari but found in B series are highly loaded push rod ends and rockers rubbing on top of valve stem.

They both have main, big end and cam shaft bearings. They both have cam followers. They both have pistons with wrist pins and rings.

The pressure wasn't my point (I've always understood some pumps wouldn't do a lot with very thin oil) but too thin an oil is a bad thing. America has shifted to 0w20 oils for economy figures and there are reports of engines originally designed for something thicker, failing. I can't see anything built in the 70s with 20w50 in mind being particularly happy with 5-30.

Old and worn engines can fail. Many might blame the oil for the wrong reason. But how many use a top spec expensive oil in an old worn engine anyway?

But it's not a 70s design. It dates from the '40s. And originally used a mono grade oil.

And originally used a

as did the ferrari

Very likely.

The B Series started out with white metal bearings and bypass oil filtration. Changed to copper/lead in the mid 50s and full flow filtering. Then eventually added a couple of extra main bearings. But is still basically an ancient design. I'd not expect one to come to any harm under normal use using any modern 'thin' oil - provided it has suitable additives. But available oils with those additives are generally 20-50 anyway - to keep oil consumption on an older design within limits.