Thanks Richard,
It is raining again today - I measured up the standard system on my 1960 GF motor, and have attached a
sketch. The ball has to lift only about 1mm to expose oil to the bush entry passage. Dimensions are the best I could measure by Vernier, so may not be perfect - a bit difficult getting the jaws where I wanted them into the small passages.
I also had a go at calculating the relative pressures of the ball and spring (for my existing spring - I cannot find my new ball and spring, so have to order another one) opposing the static oil pressure from the oil tank when motor is stopped. My old spring was 17.3 mm long, longer than you blokes have reported, so maybe some PO stretched it.! That could be why I have not experienced wet sumping. I measured the wire thickness at 0.015". Attached is also a
graph of the result.
Interesting - The spring pressure on the ball seat will take 2.336 psig, ( I assumed the spring material was Hard Drawn MB ASTM A227 - one of the options) and the oil pressure exerted on the other side of the ball is about 2.322 psig. I used a spring calculator I found on the net.
Anyway, you are right that the spring is p--s weak, and barely adequate to hold back the oil.
No doubt BSA went out of their way to ensure the anti-drain system did not reduce oil pressure to the timing side bush.
So maybe the SRM spring is the way to go. Incidentally, I ordered the springs and balls from SRM before doing the calculation, so I do hope they send me the A65 spring. Gary at SRM said they do not make the longer plug, and that they do not modify the A10 system. Gary's reply two days ago quote "
This not a mod that we do to standard engines. So the plug is something we cannot supply, have to be carefull, too long and it will block off the oil feed to the main bush, too short and spring will not be long enough to hold against oil pump body. The standard set up is fine as long as ball has a good seating."
I am still Fence-sitting.
Cheers Colin
