The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Terryb on 23.11. 2023 18:07
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Guy's, I always thought that the crank case breathing system via the cam shaft was to provide an oily mist to be emitted when the pistons came to the bottom of their stroke. So if that is the case why when reading through previous threads regarding this subject, some are experiencing substantial quantities of oil being discharged?
The reason for this question is that I have a deceased friend's 1961 A10SR to dispose of, which is experiencing regular oily discharges from the breather, which I've been asked to resolve. I myself have a 1955 A7SS and I've only seen a very small dribble from it's breather. Can I assume this Crank case pressure or would there be another reason?
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G'day Terry.
9/10 times it's wet sumping after it's been stood for a few days/weeks and will clear after the sump has been emptied. Depending on how much oil is in the sump the bigger the mess and time to clear.
If blowing oil out on a ride the oil pump may not be scavenging enough. The timed breather cork is too thin and the breather has jumped off it's peg. The rings are shot and allowing too much blow by increasing crank case pressure.
Just a few things to check.
Good luck.
Cheers
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Guy's, I always thought that the crank case breathing system via the cam shaft was to provide an oily mist to be emitted when the pistons came to the bottom of their stroke. So if that is the case why when reading through previous threads regarding this subject, some are experiencing substantial quantities of oil being discharged?
The reason for this question is that I have a deceased friend's 1961 A10SR to dispose of, which is experiencing regular oily discharges from the breather, which I've been asked to resolve. I myself have a 1955 A7SS and I've only seen a very small dribble from it's breather. Can I assume this Crank case pressure or would there be another reason?
There should be a vacuum in the crankcase, caused by the timed breather during the few seconds after start up, the breather output should then after start up (theoretically) be equal to the volume of blow by (from the pistons). It should not pick up much oil on its way out.
Having said that, some experience success with “breathers” on the rocker box that would in theory work against the oem breather, and not allow a vacuum to be created *dunno*
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My understating is that the BSA timed breathers were intended to maintain a slight vacuum in the crankcase to reduce leaks. Ideally all that would some out it oily air. My guess is its wet sumped and the rings are sticking. You could idle the engine for a while and see if it improves with some running time but I would want to know how much of the oil is int e case before trying that.
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OK thanks, I’m getting a slightly better understanding of the breather workings.
The bike has had a history of dumping oil from the breather since 2012, after its first refurb. The previous owner has tried a number of different ways to solve it, including dumping to ground, over the rear suspension and into the oil tank. The oil tank mod worked, but didn’t resolve the quantity of oil.
So, now I’ve volunteered to try and resolve it 🥴 with respect in 2015 the engine was stripped angain and restored including new pistons, rings and top end new item. So I think it’s most likely wet sumping or the breather assembly is suspect. Also I’m told that most of the oil is coming out is on startup or on tick over, don’t know about when riding.
Anyway, I have my A7SS to finish and then we will begin, so thanks for now, I will be back when I find out more. Cheers guys 👍
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Working correctly there will be some element of oil vapour from the breather, but a continuous flow indicates a sump full of oil for the reasons mentioned. Couple of things to check.......sump plate off, see what comes out, big bowl handy, and give the little ball valve down there a prod to make sure it has not stuck shut. There's a whole lot on the Forum about failure to scavenge, from leaks in the pick up pipe, oilpump gaskets, cracked castings and blocked oil return to the tank.
A good oil return to the tank soon after start up is a visual indication that the oilpump is working to scavenge the sump.
As for how the breather works......opened for a mere instant....defies all logic, but it does. Maintaining a vacuum against a twin cylinder air pump is a clever trick. Some say a bloody miracle.
Swarfy.
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Hi Terry and All,
A couple of other things to check..
Remove the timing outer cover and start the engine briefly, while you look to see if oil is leaking from the pump, spindle, body or gasket area, or if oil is leaking out between the main bush and crankcase..
I have come across one or two instances where excess leakage causes the timing gears to carry enough oil up and flood the breather area..
There were some crap quality rings about some years ago, that were either too hard or irregular shaped to seal properly
John
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John a yes on the bad rings i had some , they were useless and then i discovered gandini , perfect
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Second or third the rings thing. The rings that come with JP pistons are too hard and never seem to bed in. I too swapped them for Gandini rings and never had a issue since. I also assembled the bores dry which took a leap of faith but it was recommended to me by the engineer that bored a Ducati bevel motor for me and it seems to be a very successful ploy.
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I've been assembling pistons and rings dry (actually the merest smear of oil) for many years now, ever since reading that Hartley the pre-war tuner always did it.
Modern oil is just "too slippery" to allow rings to quickly bed in before becoming work-hardened, and there's nothing worse than seeing some old duffer still running in his bike at 30mph over 500 miles while leaving a smoke-screen that a WW1 sub-chasing destroyer would be proud of.
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On my 650 twin from another Midlands factory, that dry assembly and immediate acceleration made a noticeable difference in ring sealing.
Bloody hard to kick over, in fact!
I also made the second ring gap about 25% bigger than the top ring gap. That’s another trick I got off the internet.
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Ok guy’s, Shooter back on the road 🤪
The SR is wet sumping, obviously when the engine is hot and the oil is thinner. She’s incontinent initially until the oil thickens and after say 4-6 weeks she’ll have about a pint in the sump. So that’s why oil is being dumped out of the breather at startup.
Many thanks guys for your input. This forum is invaluable to us classic fiddlers, cheers👍
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How do you folks reckon a simple plug on the oiltank breather would work to lessen draindown into the sump on standing?
The alternatives of stripping out and replacing the anti-drain valve, or further modification as on A series unit engines (ball behind pump) or the maligned and some say risky external flow valve have all been championed, but I've never heard of simply restricting air into the oiltank to prevent the sump filling on longer periods of storage.
Seems a simple idea, would it work? Easy to find out, no need to reach for the spanners every time it comes out of the shed. Just finish your ride, park up, put in the plug and add your reminder for next time.
Swarfy.
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what about the oil cap? clingfilm ?
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How do you folks reckon a simple plug on the oiltank breather would work to lessen draindown into the sump on standing?
The alternatives of stripping out and replacing the anti-drain valve, or further modification as on A series unit engines (ball behind pump) or the maligned and some say risky external flow valve have all been championed, but I've never heard of simply restricting air into the oiltank to prevent the sump filling on longer periods of storage.
Seems a simple idea, would it work? Easy to find out, no need to reach for the spanners every time it comes out of the shed. Just finish your ride, park up, put in the plug and add your reminder for next time.
Swarfy.
G'day Swarfy.
That has merit, especially if capped off after a ride while still hot. As it all cools it would create a vacuum in the tank.
Cheers
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I would be worried about forgetting to remove the plug when setting off. With a geared pump it should be able to pull down a vacuum although with BSA tolerances that may not be a problem.
Would a new pump (eg SRM) stop the wet sumping?
John
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G'day John.
It did on my 51 A7.
Now my Cafe is wet sumping and it has roller conversion. I don't want to drill holes in an SRM pump.
Cheers
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Have you tried riding it every few days? This is what people used to do and it worked!
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G'day Rob.
Since my back fusion and my hip going west I haven't been able to fold myself up enough to get on her. I've had a new hip and modified her (std bars & footpegs + other things) to make her rideable again.
Won't be long now.
Cheers
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I must say that bike looks gorgeous! That really needs a good run *smile*
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I did say add a reminder for next time, the same goes for on/off tap in the supply line. Draindown will always occur to some degree, on all new rebuilds, new pump etc you may be lucky, but for the rest of us with original balls and springs, porous cases, you name it, we've been there. The feed side was probably only truly hermetically sealed the day it was made.
Ridden every day, sure, no big deal, dad set off for work with a bit of blue smoke, but left for a couple of months, tank will empty dripwise and it's out with the spanners, sump plate off, catch the oil, recycle.
My thought was that by preventing air entering the tank, a partial vacuum would reduce outflow under gravity, and save some start up hassle and mess.
Reckon bergs need a good sealing washer on that oiltank cap, fibre washer 67-42 should do it, same as primary case oil cap. Triumph rocker caps and washers also fit....Unless he's got a cap with a hole and a non standard tank with no breather. " Whittle a bung, bergs."
Swarfy.
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I seem to recall it would need a few weeks to come a real problem, by that I mean 1/2 or more of the oil in the engine. I've always put up with it thinking that the alternative of a tap in the oil line is just too risky. A bit like riding off with the side stand down or the petrol taps off; what idiot would ever do that...err me.
It would be possible to put a vacuum operated valve like the japanese petrol taps in but its another failure point.
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Swarfy i was thinking back to when mine had the original oil tank 40 odd years ago and i got oil mist around the tank filler cap, maybe that was in need of a new seal. at present i am one of the lucky ones who has a dance around the garage when i take the screwed cap off the ally oil tank and the oil is there at the same level after 2 or 3 months of winter lay up *yeah*
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Recent post from a new member ticks all the boxes for every problem possible with a worn engine. Excess oil in the combustion chambers is down to worn bores, pistons and ring problems (broken, worn or the wrong ones), oil coming down worn valve guides, along with too much oil in the sump......it is a so called dry sump system, oil in the tank, not in the sump.
Oil in the sump, (our old friend wet sumping) due to draindown from the tank or failure to scavenge will result in oil from the breather outlet and increased crankcase pressure venting oil where it can, into the primary case as an example. Running with a rocker cover removed, a bit like taking the oil cap of an old Ford Crossflow, to see how much pressure there is. With piston blow by there will be pressure and combustion smoke, an indication of bore and piston problems.
So valve guides, pistons, rings, bores and scavenge side along with the pick up pipe and its little ball valve all need cleaning and close inspection. Anti wet sump valve in the crankcase likes an occasional blow through with carb cleaner. All easy things to do with the engine in bits.
Posted here as a general summary, there is enough on the Forum about every aspect of the system, and in general the faults and causes of trouble are easy to spot.
Swarfy.
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Obviously this is a well-worn thread (excuse the pun). A previous poster had a big problems with this and found that the cure was to change the filter screen in the sump. Presumably, a pattern filter screen had mesh which was too fine and wasn't allowing the oil to drain into the bottom of the sump quickly enough. Another problem, which I don't think has been mentioned in this most recent thread, is leaks in the pickup tube. I've heard of tubes which have rust pin holes and also tubes which aren't a good fit in the crankcase half, so the pump sucks air until the oil level covers the leaky part of the tube which means the bike is running with too much oil in the sump.
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Great point about the integrity of the sealing of the pick-up tube.
The tube often cops knocks when the crankcase is handled (dropped / placed on work bench, washed, etc) because it protrudes below the sump plate mounting surface.
This is a reason that sometimes the pickup doesn't align with the hole in the mesh screen.
So, oil can leak into the sump from above the ball in the bottom of the pick-up tube if the tube has loosened into the crankcase, or the alloy has cracked, or the steel tube has fractured, or the brazing has failed between the steel "holder" of the ball, and the tube.
Another issue I had, involved the steel pin riveted into the holder, above the ball, to prevent the ball moving north up the pipe.
The pin was not sealing in the holder, beneath the riveted ends. I silver soldered each end, and yippee, wet sumping reduced, and the return oil flow improved.
To identify any of these issues, even on an engine still in the bike, remove the oil pump and blow compressed air into the drilling that connects to the pickup in the sump.
The sump plate needs to be removed. Wear safety glasses before sticking your noggin under the sump. If the ball and the tube, riveted pin, etc are sealing perfectly, no air leakage will occur.
Holding an air gun with a rubber tipped nozzle into the port will work.
I have machined a blanking plate to replace the oil pump, with a fitting over the scavenge pump port to connect the air line; makes this an easy one person process.
These checks should be done during every rebuild.
If you make a blanking plate which an air hose can be connected to, then the crankcase half can be immersed in water which is a good test for leakage paths.
Basic fettling, but worthwhile.
Cheers,
Richard