Dry Sump Lubrication

[ajmac]

Right... I realise it has been around for years and is simple in principle, but how in practice do you stop the lower pistons on a Radial engine filling up with oil? Same question goes for the Multibank lower banks, where the cylinder is lower than the crank centre line.

[Bodge Deep]

USAAF Proceedure on aircraft radials was to rotate them by hand periodically... but not sure how you'd do it on armoured vehicles short of turning over without ignition...

[Enigma]

I've seen a Hellcat being handcranked to distribute the oil.

[Adrian Barrell]

The oil enters a radial engine oil pump close to the centre of the engine and so there is no large amount to fill up the cylinders. The scavenge pump(s) have a greater capacity than the pressure pump and the lower cylinders have scavenge bowls on them.

 

The problem comes from the relatively small amount of oil on the rod side of the piston leaking past the rings. Starting the engine without clearing this results in bent rods at best, blown cylinders at worst!

 

It is normal in aircraft to hand prop a few blades to clear any oil and in radial powered tanks, a hand crank is used through the starter motor gearing to achieve the same effect. This is only really necessary if the engine has sat overnight though this would depend on individual engines.

 

The multibank lower blocks are actually inclined by 5 degrees so there should be no oil above the piston. There was a potential problem of fuel filling a cylinder on the early engines where the carbs were mounted directly on the manifolds. There is a fuel cut off solenoid by the filter to help but the later engines moved the carbs up to the top of the engine to put them above the fuel level.

[ajmac]

the lower cylinders have scavenge bowls on them.

 

That's the bit that interested me.