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« on: 26 November, 2020, 16:10:38 »
Borrowed this reply from another forum. Hope it helps, should cover most old British Bikes.
You'll always be able to find this problem on forums but hardly ever get the answer you need. Chucking oil all over the floor of the kitchen or smoking out the kids in the living room when you rev up doesn't really help keep you out of the doghouse.
So here's a fairly long list of the more common reasons that you may want to investigate - these engines are pretty simple to work on so you're not going to solve anything unless to actually climb into them with your trusty spanners:
1 Some form of obstruction in your oil pump. Probably a minuscule spec or gnat's tadger lodged under the return oil pump check ball. Take the pump to bits on a nice clean cloth or kitchen towel so you can inspect, clean and reassemble.
2 The oil pump check ball not seating in the brass body. You can see that it doesn't 'sit' right into the circular cavity properly. Get a drift and give the ball bearing a whack with the hammer. Make sure it still operates correctly when you reassemble the pump (ie the ball bearing isn't stuck).
3 The oil pump check ball cover is seated properly and the ball retaining spring is there and in good condition.
4 The oil pump pistons are not worn, are smooth and fit snugly into the brass body.
5 If there's any doubt as to the condition of the pump or any of the parts then buy a new one. A good quality one, NOT the cheapest thing you can find on ebay.
6 You've been a bit too enthusiastic with the silicon, gasket compound, sticky stuff, chewing gum, etc when reassembling the engine and have blocked oil ways. Or haven't been enthusiastic enough when cleaning out the oil ways after working on that project case or after having all the parts sandblasted or powder coated. Make sure all the return ways are clear and open - blow through the scavenge pipe to oil pump, blow through the oil pump to oil block, clean the oil block and metal junction pipes and blow through the return oil line, blow through the 'T' piece junction to the rocker boxes and make sure the smaller diameter entrance to the oil bag is clear.
7 The oil scavenge pipe in the sump (the pipe you can see if you look up into the sump when you remove the sump plug) has an air leak. Push a rubber pipe over the scavenge pipe (not too much or it'll be a bugger to get off, just enough to get a seal) and blow into the pipe - if you can blow into it then you have a leak. If you can't blow into it then suck on the rubber pipe like a straw. Once you have a vacuum put your tongue into the end of the pipe and let the vacuum hold it there. If all is tight after 30 seconds or so the all is ok.
8 The oil pump isn't seated properly against the crankcase. This would also show as a leak on the blow/suck test above. The oil pump can be pushed off of the crankcase by the inlet cam not being seated correctly (on the earlier models with the breather on the end of the cam the butterfly valve and spring are not located correctly).
9 A porous crankcase (some of the cases just weren't made that well) this would also show up on the blow/suck test. There are treatments for this condition as it's not just older models that suffer from this (I've never seen one)
10 An air leak caused by the oil way bolt on the crankcase below the oil pump. (On 'B' range bikes) The bolt is part number E4539 in the parts catalogue.
11 Blockage caused by either the gasket between the oil pump and the crankcase or the gasket between the oil pipe junction block and the crankcase. Sometimes the gaskets aren't cut too well.
12 Overfilling the oil tank
13 Stuck or broken oil pressure relief valve. Take the valve off, take it apart and make sure the piston operates and that the spring is in good condition. Any doubt, get a new one.
14 Blocked, or even partially blocked oil tank vent pipe.
15 Shortened crankcase vent pipe - the pipe normally runs under the seat and over the back wheel, shorten it and you can expect some spots of oil on the floor.
16 Sump scavenge pipe too long or loose in the crankcase that then gets cut off when you replace the sump plug. If you remove the sump plug gasket and make a paper one this could be enough to close off the scavenge pipe's open end. (If the copper washer leaks even after annealing or you haven't got one use a pushrod tube oil seal - one of the orange ones).
17 The sump plug mesh/screen is too fine or blocked by black goo. The screens on the 1960 'C' range and the 1968 'B' range bikes are suspect, get a new one.
18 Big bore kits, installation of new pistons and rings. Bedding in can cause the crankcase pressure to rise and blow out of the breather hose. This should calm down once the rings are bedded in. You can bed the rings in on the build using all sorts of home remedies (even bi carb into the carbs) but I've never had the bollox to potentially balls up a new rebuild.
That should give you something to occupy you if you have the annoying problem of wet sumping or producing a large puddle of oil from the breather pipe every time you stop on your mum's new driveway.
The whole list of checks shouldn't take you much time to complete once you find your way round the timing side of the engine. You'll get oily hands, a few puddles on the floor, get yourself a few gaskets before you start and be prepared to have that inner glow of triumph engine knowledge once you solve the issue.
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