Article on The Internet Mini Encyclopædia
Oil leak prevention: Rocker Cover Gasket (added 20 Dec 2002 from Simon D)
If you have the chance, slip the new rocker cover gasket
over the top of the rocker cover for a couple of days and you will find that
it has 'learnt' the correct shape to be!!!!
Oil codes (eg: 20w50)
Most oils use a code such as 10w40.
The first figure is the viscosity rating at 0'C, the 'W' stands for Winter (don't worry, it is just to separate the figures! sometimes you see 10/40), and the second number is the viscosity rating at 100'C.
The second number is the important one, as this is when the engine is hot.
For a mini engine you want 40 minimum, preferably 50. (eg: Valvoline 20W50, GTX 15W50)
The first number is the viscosity when cold. It helps if the oil is thinner when cold, so that it circulates quickly to protect the parts. For a mini 10, 15 or 20 is best.
Viscosity 'Rating' NOT actual viscosity (in cP etc)
Also known as the 'Grade' of the oil (hence Multigrade, Hypergrade names)
All oil reduces in viscosity when it gets hot. This is a behaviour of hydrocarbonous molecules.
If you draw a graph of temp vs viscosity then various oils will make various lines across the graph.
These lines are the grades or ratings.
Natural oils (eg SAE30) will stick to one line, thinning out when hot, but modern oils have those helix molecules added to try to reduce the amount the oil thins out when hot, and make the oil behave like a different natural oil at different temperatures .
You end up with, for example, an oil which acts like a natural grade 15 oil(quite thick cold, very thin hot) when cold and a natural 50 grade (dead thick cold, quite thick hot) when hot.....hence "15W50" (pretty thick cold AND hot)
You can't print the viscosity figure (in CentiPoise etc) on the oil bottle because it varies with temperature. You could show a list of temps, or show a graph...
....or just state the characteristics at 0'C and 100'C. ...which they do.
You can see that a 'perfect' oil would have the same viscosity when cold or hot. This would be something like 0W100 oil. This isn't available (yet), but modern synthetic oils come in 0W60 (eg: mobil1). These are very expensive.
Synthetics are not much good in mini engines due to the shared gearbox. The gears mash up the special chain molecules and thin out the oil.
Synthetics shouldn't be mixed with mineral oils either.
Many cheap 20w50 oils are of poor quality and get far to thin at high temperatures leading to poor oil pressure.
The general favourites for mini owners are Castrol GTX 15W50, Duckhams Q 20W50, Duckhams Hypergrade 15W50 or Valvoline Racing oil 20W50.
Oil, explanation of movement round the engine
Oil gets sucked up from the sump up to about half way up the back of the block.
Then it goes into a pump in the clutch end of the block behind the transfer housing.
From there it goes past the relief valve (which returns some oil to the sump if the pressure is too high) and out of the block to the cooler (if fitted) then to the filter.
It goes from the outside of the filter to the inside of the filter and into the block. There is a little valve in the filter head that opens if the filter gets blocked and lets oil bypass the filter.
From there it goes into the oil galleries (this is where the pressure is sensed) and feeds the main bearings which in turn feed the big ends and cam followers.
There is also another that goes from the main galleries up the back of the block and into the head that feeds the rockers.
The bearings leak oil out back into the sump.
The cam followers are lubricated by the oil that drips off the rockers, down the pushrod holes onto the followers then down into the sump.
The transfer gears are oiled from the spray from the gearbox gears throwing oil around. The oil is caught in little vanes in the transfer housing that directs the oil to the transfer gear bearings
Oil pickup, centre type, fitting
"How do I go about fitting a center oil pickup???"
Engine out. Gearbox off. Remove layshaft. Remove old pickup. Try to fit COPU. Hammer to shape. Try again. Try again. Hammer some more. Fit it. Re-fit layshaft. Re-build engine. Refit engine.
Oil cooler orientation
Oil should flow in at the bottom and out of the top. That way, oil is in contact with the maximum internal surface area of the cooler. If you pump it in at the top, it can just "fall" straight to the bottom and out again without being cooled (or not much anyway). It's the same as with a Leibig condensor (for anyone who can remember them from their schooldays).
Oil unions, thread size
1/2" BSP oil cooler hose and unions could be used from block to filter head, but the block union is 5/8 UNF with copper washer sealing, not 1/2". The thread on the oil cooler itself is 1/2" BSP parallel. The thread in the standard oil filter head is 1/4" BSP and the hose thread is TAPERED. The thread in the block output may be different (1/4"BSP, or possibly 3/8") but it is definitely parallel, not tapered. The "inches" is the pipe INTERNAL diameter, not the EXTERNAL thread diameter as with UNF/Metric bolts etc.
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