Well I got a very quick reply from Penrite technical support and I quote:

CLASSIC MINI 20W-50 (Mineral) - https://penriteoil.com.au/products/clas ... 50-mineral - has a typical zinc level of about 1390 ppm and has been designed to provide an excellent combination of engine protection and smooth gear shifts.

If the engine is not burning oil continue to use Classic Mini, but if you are needing to top up substantially between services then HPR 30 is a good option.

Thanks for your interest in Penrite.

HPR has a higher level of zinc (1530ppm vs 1390ppm for classic mini) and being 20W-60 vs 20W-50, I'm guessing that's why the HPR is better for engines using oil.

Minnie (a 1963 rebuilt 850) breathes a fair bit out of the tappet chest side plate and being the original version, this plate just has a tube pointing down over the diff. The engine itself doesn't use oil other than a very small puff of blue smoke on start up when warm after it's been sitting for say 30 minutes and I've put this down to dodgy valve stem seals. The head was fully reconditioned but given the poor rubber we seem to get now, I'm thinking they're worn or perished already. There was no smoke at all for the first 1,500 miles but then it started. No smoke at all on start up when cold and been sitting for a week or so. The amount of smoke doesn't worry me and I reckon I'll leave well enough alone and not replace the seals unless they get a lot worse.

Do you blokes think the HPR would help reduce the breather a bit?

Thanks Rocky

The later breather would stop the oil loss, not necessary the breathing lthough if you were to connect to the carb you would not notice it, but you probably alr3ady know this.

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Cheers Dave.

As the one who started this thread it is good to see a varied wealth of info being presented. I was using the old classic 20w50 which was described as being especially suitable to bmc minis. This was then replaced by classic light 20w60. A while later Classic Mini appeared on the market at 20w50.
I purchased a bulk amount of Classic 20w50 which has now run out. My latest choice is gulf western.

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Cheers Dave.

G'day Dave - re the breather.

When I first got her on the road, I didn't have anything connected to the breather tube on the plate and the oil from it just ran down onto the diff and made a mess. So I made up a sort of catch can by running some heater hose from the breather tube up to the air cleaner and put a tap and drain pipe in the U part of that hose so I could drain the oil every so often. However, I think I may have restricted the breather a bit as I started to notice a slight oil weep from the clutch casing.

So I took the homemade catch can off and just put a length of hose onto the breather tube and ran that down towards the ground so the oil doesn't make a mess on the diff but it does get blown under the car a bit on the passenger side. Inbuilt rust proofing.

I have got a S side plate that has a larger opening plus a canister on it. I was going to fit it but access is a bit tight with the manifolds on and I'm a bit reluctant to pull it all apart again in case I make matters worse and end up with more leaks - either manifolds or side plates. I assembled everything on the engine before I put it in the car.

The tappet cover vent is plumbed into the air cleaner.

Cheers Rocky

The 1275s here all have the clutch housing breather connected to the carb, to stop the dipstick lifting tbus oil loss.
The 1100 has a canister style side cover also connected to the carb and the rocker cover to the filter. I tried various things including homemade systems PCVs etc but the standard works best.
There used to be a rubber side plate gasket which sealed better than the cork ones.

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Cheers Dave.