C15 Bearing Bush (steel Outer In Case)

[nigelog]

Hi, on stripping C15D engine with timing side bush, bush was seriously shot. Phosphur/bronze bush had either spun or been fitted incorrectly as the oil feed visible (pointing to anti sump valve) had closed to a eclipse equally about 10% of throughway. After removing bronze bush to replace I noticed that even though the steel case insert has machined faces to locate it vertically when fitted in case, the oil feed holes here do not align correctly. There is a devience of a few degrees. To open the oilway fully I would have to enlarge one side of the oil feed holes (in the case I would have thought preferable). Which of the two is less likely to cause a problem, opening the feed to the anti sump valve, or opening the feed to the pressure release valve. I would appreciate any help as it cannot be left as is, as another rebuild with the same inherent problem will just result in another bush failure. Many thanks. Nigel

[chewy]

Hi Nigel just read your enqy. out of interest to see if anyone has encountered your problem which appears to be getting oil to feed through the bush, Firstly remember phosphor bronze is "porous" so it should soak up oil from any pressurised supply. Is it possible to hand machine the oilway in the case to ensure supply at the "feedhole" in the bush (if this is what you are describing) using for example a small tungsten carbide burr in an airtool? Finally I don't know this engine at all but if the pressure release valve is to be of any use surely it must be on the pressure or supply side of the equation,.. is it funnctioning correctly? This may all be dribble " but it always helps to talk things over eh?

[nigelog]

Hi Chewy,

as you state the pressure release valve should be on feed/supply side but is not quite. BSA engineering no doubt. Following the feed route the oil leaves pump and heads through the crankcase to a non-return valve. This one of the two oilways for timingbush.

Looking from the inside of the case there are 2 oilways in the bearing recess 1. drilled at 6 O'Clock is the non return valve 2. drilled at 9 O'Clock is the pressure release valve oilway.

Once through the non-return valve the oil passes through an oilway in the steel bearing outer seat to the bearing bush itself. It has two paths from here, first is through an oilway in the inner bearing bush to the crank to feed the big end, second in the case of over pressure is though the oilway at 9 O'Clock to be dumped into sump.

Now I've had a better look at it, leaving aside the phosphur/bronze bush which could have turned, if the bush outer is fitted with the machined faces located in their keepers (which it has to to seat) the oilway at 6 O'Clock (feed) is restricted by 80%. The oilway at 9 O'Clock is OK (dump to sump). The pressurised oil feed through the bush/crankpin to the big end must have been abyssmal and luckily the big end is the only bearing that does not need replacement.

I will need to enlarge the mouth of the case at 6 O'Clock for the oilways in the outer seat to function. As you state dremel/burr is the way to go. On further inspection the inner bush seat also has oilways one of which should line up with the oilway in the crankpin. Again the line up in this case is retricted by 80%. This seat also has to be replaced so I will align on re-assembly.

How this was not noticed on last assembly is a moot point and may even have been BSA as I can see no evidence of futher rebuild. It is 30 years since I looked inside any bike and even in those days I would have just re-assembled and ridden on until the next bang. Either life was easier then or money is harder to come by now to be wasting. Cost of this bearing job for the mains

Timing bush inner