Accusump Set Up

In a vain effort to find something useful to do I thought it was time to set the accusump up - however this would include running the engine again....... shame!

The accusump had been pressurised prior to the cam break in run to avoid it taking oil out of the system. The big question is how much oil to add? The accusump will store oil according to the pressure in the oil system at shutdown.

I thought it would be a good idea to calculate the theoretical amount required and compare this against the actual amount added. The main problem I could see is that as the volume of oil stored is dependant upon pressure, this means that the volume will be temperature dependant as oil pressure drops with increasing temperature. So back to some schoolboy Physics/Chemistry and the theory is as follows:So with a 30 psi difference in oil pressure at idle between hot and cold the actual variation in volume stored will only be 0.15 litres (not a great deal with no danger of overfilling). This range of 50-80 should cover the normal operating range of the engine: 80 cold at idle, 50 hot at idle and presumably 80 ish hot at high rpm. However this may need some adjustment once it's on the road.

So the theory says that I should need to add around 1.8 litres of oil, the aim would be to have the desired level when cold. This would mean a theoretical overfilling of 0.15 litres when hot, but oil would be circulating in the engine so would not be high in the sump. The main issue would be not to end up with a low level when the Accusump takes more oil when cold.

So the Accusump was bled down to a 10 psi pre-charge. I then added a litre of oil and started up. The engine oil pressure rose to around 75 psi as did the gauge on the accusump (the accusump was not energised so it would not flow oil back into the system). I ran the engine for a couple of minutes (before it warmed up) to get oil round the system and then shutdown. I waited 30 minutes and then topped up the cold level bit by bit until it was at the original level. I ended up adding somewhere around 1.7 litres.

The engine was restarted and warmed up (with the accusump energised this time). As the oil warmed up the pressure reduced to around 50 psi. The engine was then shut down, left for half an hour and checked again and found to be only marginally over the original level.

Job done and a good excuse to run the engine again...... it's getting addictive!!

During this process I noted that the pressures shown on the accusump gauge were not the same as those on the oil pressure gauge?? I checked the accusump pressures with an air pressure gauge... OK. Checked the earthing of the oil pressure gauge - bit too much ptfe tape causing a poor earth I think. The revised pressures are 75 psi cold at idle and 50-55 hot at idle - even better than before - so I had to work everything out again which is what you see above.

Everytime I have run the engine I have always taken the PCV breather off the rocker cover for a moment and looked inside - it has always been comforting to find floods of oil coming up the pushrods and over the rockers - even at 1500 rpm!