Me too; I share the concerns about the A65 ball arrangement; I don't like what I have measured!. Don’t forget that the ball will have pressure UNDER it at the same time that oil is flowing partially around it.
I am wondering if the throttling effect of the A65 ball arrangement has contributed to some of the crank shaft failures they tend to have. I am not happy with it as BSA have done it, and have in mind a simple mod to the A65 arrangement.
I have also measured the arrangements for the A10, and the A65 anti-siphon ball arrangement, and have nearly completed drawing both arrangements in Solidworks, which is a 3D modelling program we use for mechanical design (including fluid power manifold blocks).
I have nearly completed machining a Perspex block, which I will test the A10 pump on, with the A65 arrangement beneath it. I will be measuring pressure upstream and downstream of the ball, and changing the depth of the hole, to work out what depth and spring combination works best. I have also included a cavity to accept an A10 relief valve.
When I have proved the best arrangement, I will publish on the forum.
I will also be using compressed air blown in at a reduced (regulated) pressure not exceeding 50 psi, introduced via a modified oil relief valve, to enable this to be done whilst the engine is together. I will provide details for a jig, so the hole can be drilled square, and to the correct depth.
Pressurising the crankshaft / bearing arrangement like this will also give a visual of leakage between the journal / bearing, and the bearing / crankcase half, which will shock people; an over looked area of leakage. I discovered this many years ago when blowing air into the oil delivery gallery to an engine (just remove the oil pump to do this). There was as much air leaking from around the outside of the timing bush, as from between the crankshaft and the (worn) bore of the bush! Most the A10 engines I have checked have elongated bores for the timing bush; It typically takes 0.012" - 0.015" machining to clean the bore up. I believe this is because of the stresses (crankshaft flex; there is no middle support bearing) the crankcase is subjected to with high mileage engines, increased CR, 18 year olds revving the Be Jesus out of them, etc.
Therefore, after the hole is bored true (cleaned up) and an oversize bush (0.002" interference) is shrunk in, it can be line bored, and oil leakage around the outside of the bush is eliminated. A solid phosphor bronze bush is best, as its coefficient of expansion is closer to the expansion rate of the aluminium crankcase, than a steel-backed bush is. Therefore you are more likely to prevent leakage between the bush / crankcase when it is hot.
Any damage to the crankcase timing bush bore (scratches, "tramlines") must be avoided, as this will be a permanent oil leakage path. This can (will) be caused by removal and fitting bushes to a cold crankcase.
Richard
