The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Andy Williams on 03.06. 2024 11:56
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Good morning, towards the end of last year my Super Rocket started to become difficult to start when hot. After trying various things I opted for a mag rebuild. I entrusted the removal and re-instillation of the Magneto to a someone who is extremely experienced in maintaining this kind of bike.
Unfortunately for various reasons including ill health and a house move the work took a long time but when it was eventually completed i collected a bike that fired up instantly hot or cold. Now this is where my troubles began after arriving home i found the rear wheel covered in oil that an investigation showed was being forced from the engine breather on the left side of the engine. I know the old girl suffers from wet sumping which normally shows itself with much smoke on start up (if i haven't used the biked for a few weeks). There was no smoke when startling up when the bike when collected with leaves me to believe the sump had been drained prior to me collecting the bike.
The engine condition is to the best of my knowledge really good with excellent compression and no oil leaks.
I removed the sump to ensure that there was no excessive oil but after reinstalling and starting its still pushing oil from the breather.
The oil return to the tank is excellent with a strong flow.
I have noted that I can feel air pressure "pulsing" from the breather along with the oil. i am assuming that if the ball in the sump pick up was stuck then i would not be getting a strong return to the tank is this correct? could the pressure release valve on the front on the right side crank case be causing this? Finally if the fault lies with the corks in the timed breather would i still be able to feel the "air" pulsing from the breather?
thanks for looking and hope someone can help!
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Before going deeper I would suggest a jet wash and a run to see if this is a recurrent problem or a one off. The timed breather is pretty simple and there's quite a bit of leeway on the cork washer before it looses drive, and even then the oil would not come out the breather hole. If there's crank case compression you really need to do a compression test but it sounds like there is enough compression for easy starting. If I recall correctly the timed breather pick is quite high in the engine so even with blow but I wouldn't expect much oil, more mist.
My inclination is wet sumping and a one off problem but only another run will tell.
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Very many thanks for your prompt response!
I have cleaned the old girl off and tried another run 3 times now in the hope that the fault will miraculously disappear in vain unfortunately.
As previously stated I have removed the sump to ensure that wet sumping is not the issue, and gone for a run immediately after with no change.
i am beginning to wounder if the oil being returned to the tank is actually excessive and that possibly there is being too much oil being supplied to the crank cases in the 1st place but dont know if this is possible and if so what could cause it?
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OK, check out the thread on here "baffled confused and covered in oil". Its a long discussion because its baffled us all (well except for one person who nailed it early on..) . Worth a read, could be your issue. The sump gauze does not pass enough oil and the level builds up. If you have the flat bolt in gauze try a run with it out.
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Again many thanks, will have a good read in a moment but would not the fact that i have a really good return to the tank rule this out?
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That's what we thought, but the discussion is very interesting. What oil are you using and do you have the original domed gauze or the aftermarket flat one?
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Im using Comma Classic 20 50 at the moment, if memory serves me its a flat gauze filter.
Seems really strange that all was well (oil wise) until the bike was off the road for about 3 months?
think will take off the sump again completely drain clean gauze and re-check the ball and keep finger crossed!
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A clue to the problem is what happens to the oil level in the tank. After a run the level should be more or less the same as when you set off, assuming on start up there was time allowed for the pump to scavenge any oil drained down into the sump on standing.
A constantly falling level shows oil accumulating in the sump, which is then vented via the breather. Just wondering whether all the bits you sent off were the same ones that came back.....
Try starting from scratch, sump plate off, crankcase empty, oiltank drained, refilled with recommended capacity. Some folks top up the tank, not realising all the oil is hiding in the crankcase. It's a dry sump system, not like your more modern bikes. The rocker feed is one culprit, too much oil bled off means less going back to the tank, more in the sump, eventually overwhelming the scavenge capacity.
Swarfy.
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Yes, I have a cartridge filter in the return and one issue I've found is that it smooths the return flow. So whereas without a return filter the return flow is obviously intermittent once the scavenge pump as cleared any surplus, with the filter its continuous but frothy so the filter must be breaking up the bubbles. This makes it much harder to see what's going on.
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I'm still really confused must of the advice points to poor scavenging and poor return resulting in excess oil in the crank cases. My return is very strong seems almost too much it really is returning under pressure it is leaving the return pipe and hitting the opposite side of the tank under pressure! As the return side of the pump has a higher capacity than the feed can't work out how this is possible? Sump is off will allow it to drain overnight and try again tomorrow. The ball seems to be free can easily ouch it up?
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G'day Andy *welcome*
As Rob mentioned check out https://www.a7a10.net/forum/index.php?topic=14612.0 It's a long thread 13 pages so sit back with your favourite beverage. It lists many causes for your problem. Just strange only started after a magneto refurb.
The PVR (pressure release valve) wouldn't be a cause as any blow off still ends in the sump and the scavenge side of the pump delivers more volume than the pressure side.
Now get over to Intro's and give us your story (credit card details etc).
Cheers
edit: Just saw your last post. The return should be strong but after a minute or so should turn into spurts or at least bubbles in the stream.
Have you spoken to the fella that did the work on your bike?
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Good call about asking the fella who did the work. I've known some absolutely baffling problems caused by someone trying to be helpful and doing an extra bit of work and not mentioning it. It happened to me once, I got a car back from some paint work and the bulb failure light was on. I tried everything and swapped all the bulbs (or so I thought). In the end I rang the guy and he said, "oh yes, I noticed one of your number plate lights was out so I popped one in". He'd put in the wrong wattage but it looked the same as the correct one.
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How long was the bike left unused? I’m wondering if the rings are stuck and a compression test should reveal that, the bypass gases could cause the breather to “work harder”, a related possibility is the crankshaft oil seal has popped out, easily tested by removing the primary case filler plug.
My thinking is check “whats changed” rather than go through the “baffled” thread but that thread does have a comprehensive list of possible causes….
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Very many thanks for all the reply's and advice.
Unfortunately due to a house move and family illness the chap who did the work is unfortunately very much under the radar at the moment so no help from that direction.
The bike was off the road for about 3 months in between mag removal rebuild and re installation in which time i am sure the entire oil tank contents would have found their way into the sump so I'm sure it would have been drained prior to 1st start up after the mag work and before i collected it.
For information she has an SRM sump plate with the built in drain plug.
Obviously stuck rings is a possibility but although unscientific the comprehension feels fine and she starts and runs fine no smoke or any other indication that something is wrong.
I keep coming back to the amount of oil being returned and the pressure it is returning at, even after a run when i would have though wet sumping in not possible the flow rate seems to me to be possible excessive indication too much oil being fed to the engine but who is this possible?
thanks again.
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Going back to your first post and whats come out the breather (pipe) on the engine….the aim of the timed breather is to cause a vacuum in the cases, on start up the gases are pushed out of the breather pipe on the left hand case but this will reduce as a vacuum gets established, an equilibrium will occur where the gases that bypass the pistons will equal the volume of gases exiting the breather pipe (noting some engines just have a hole and no pipe).
My bike does not smoke when wet sumped, or pump oil out of the breather, but others do apparently, but I don’t for 100% know why as the timed breather is quite high up in the case, I guess so much oil gets flung about that some gets through the timed breather and into the internal breather passages in the cases.
Have you changed the oil since the bike was returned? I ask as if oil was drained then I would not put it back, but would fill with new oil, and maybe the wrong oil was used? *dunno*
The classic error of course is to top the oil tank up, when 1/2 the oil is actually in the sump, which results in oil everywhere!
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And to add that having had an engine with stuck and broke rings they are very hard to start and smoke horrendously so I agree, this is not likely. Is it a possibility that the oil came out the tank overflow? Does that have a pipe on it to anywhere? But you say its happened several times so I'm clutching at straws.
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Hi no oil change (well planed anyway!) since getting the bike back however have had to top up due to the amount of oil loss, (topped up after having the sump off to drain any contents).
Have always used this oil so cant see that this would be an issue?
Think a lot more reading and trials seems to be the order of the day. *conf*
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Hi Andy,
Pull the timing cover and check the breather sleeve cork washer
There should be no end play on the top hat breather, even a small amount can cause your problem.
It should be possible to rotate the top hat a
little on its drive peg , but it should have some resistance.
Is the SRM sump plate fitted so the magnetic plug is as far away as possible from the pickup tube?
I had a problem on a bike where the magnet stuck the ball closed
Unlikely in your case but you never know *????*
John
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when the magneto was refitted was the cork washer (re)fitted????
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Again very many thanks, but is the Cork washer not behind the inner timing cover and as such would not have to be disturbed during the magneto installation?
For information the SRM sump plate has been on the bike since i have owned it about 5 years and has not been a problem but you never know?
I must say that it does seem a massive coincidence that the problem only started post the mag work?
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Andy,
Is the oil release from the breather port profuse or spattery? The couple of times I’ve sent oil through the breather, due to wet sumping, the flow was profuse, leaving a puddle under the bike. Until now, I haven’t thought that much about the mechanism for this, but the basic element has to be the magneto/breather side of the timing cover filling with oil. How (I ask myself)? I believe it must be that the flooded crankcase is causing the timing gear chain to bring up more oil than can be drained from the breather side after being flung from the magneto gear. Regardless of whether this idea is correct for wet sumping, it seems profuse flow with no wet sumping still requires the breather side of the cover to be flooded. This would make me want to check for obstruction of the drain hole at the bottom of that compartment. Now, back to Chaterlea John’s point about the cork gasket, I “think” (not “believe”) that a bad cork gasket would result in spattering rather than profuse flow from the breather port.
Looking forward to any challenging Chaterlea chastisement if necessary.
Richard L.
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Many thanks Richard I would describe the oil loss as somewhere in between profuse and spattery the flow is fast enough to provide a fairly constant drip resulting in a small pool of oil in a very short space of time!
think i will be removing the timing cover after work today!
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Another possibility just popped into my head (plenty of vacancy available for new tenants). If the pocket in the timing cover for the timed breather has been packed with grease, leakage due to the cork gasket could not drain. All this is amongst my quandary over the effects of the reducing disc in the throat if the breather. Maybe that disc allows leakage from the cork to accumulate for a faster outflow.
Richard L.
P.S. Grease in the breather pocket would also mean no breathing, just leaking.
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Hi All,
I wrote some time ago about an A10 that took to blowing oil out the breather after an extensive and expensive overhaul.
It eventually transpired that a leak on the end feed block that's attached to the outer timing cover caused oil to be carried up to the breather by the timing gears and onward out through the breather.
I am just wondering if a leak at the oil pump or its gasket could do the same?
John
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Now while the problem arose after magneto work, that's not to say that is the root cause. CJ has a very valid point here, notwithstanding return to the tank indicates the pump is working fine, but a leak here compromises flow to the engine and also give possible scope for a larger than usual return volume. As a first step it is worth taking off the timing cover and checking the security of the pump, and whether or not the keyhole above it back to the sump is clear. The breather bush can be checked for in/out movement....there should be none, and the bush location on the cam gear drive peg checked by observing the bush rotate as the engine is kicked over. Removing the pump to examine involves a fair bit of dismantling, pump drive worm and locking nut are left hand threads. So only tackle as a last resort.
As a further test, idling the motor over a large catch tray, timing cover off, will show the amount of oil coming from the timing bush, or any leak between the bush and crankcase. This is extremely messy, frightening if you get Niagra Falls, and keep an eye on the rapidly falling oil tank level.
Swarfy.
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Again many thanks to you all, timing cover is off at the moment removed it last night there doesn't appear to be any lateral (horizontal) movement between the cork and the breather there is a small amount of rotational movement. will take the opportunity to check the other areas suggested.
Many thanks
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This is baffling me, I've gone to the shed and had a look at an inner timing cover, rotary breather and set of cases. The only way into the breather is though the hole in the end of the rotating part and this is in the upper rear compartment of the outer timing chest. There is 1/2" dia cast hole under the breather rotor into the inner timing chest. The cases have a similar sized hole into the crank chamber about level with this and just forward, level with the idler bush.
For "solid" oil to be getting into the breather the cases would have to be half full which seems very unlikely. Even if there is a lot of oil around the timing gears it the other side of the inner cover.
One thing I did notice is that the breather passage goes across the cases in front of the camshaft and passes near a drilling down to the camshaft bush. This has to be re-drilled when a new bush is fitted and a real long shot (very unlikely) is that there is some breach between the breather and cam bush gravity feed. You could test for this by putting a finger over the breather outlet and blowing in the hole in the inner timing cover, it should be blocked.
The first communication from the inner to the outer chamber where the breather pick up is about 3" up from the bottom of the timing chest so I'm still baffled.
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thanks Rob the good new is that my mate who has a vast amount more knowledge than me will have a look at the weekend!
tonight i will be replace the sump, timing cover and rig up an extended breather pipe to the rear of the bike then top up oil ready for dropping it off at the weekend. He is going to go through everything and replace the cork just as a matter of course.
will let you all know the outcome, very many thanks to all who have offered advice.
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This is baffling me, I've gone to the shed and had a look at an inner timing cover, rotary breather and set of cases. The only way into the breather is though the hole in the end of the rotating part and this is in the upper rear compartment of the outer timing chest. There is 1/2" dia cast hole under the breather rotor into the inner timing chest. The cases have a similar sized hole into the crank chamber about level with this and just forward, level with the idler bush.
For "solid" oil to be getting into the breather the cases would have to be half full which seems very unlikely. Even if there is a lot of oil around the timing gears it the other side of the inner cover.
One thing I did notice is that the breather passage goes across the cases in front of the camshaft and passes near a drilling down to the camshaft bush. This has to be re-drilled when a new bush is fitted and a real long shot (very unlikely) is that there is some breach between the breather and cam bush gravity feed. You could test for this by putting a finger over the breather outlet and blowing in the hole in the inner timing cover, it should be blocked.
The first communication from the inner to the outer chamber where the breather pick up is about 3" up from the bottom of the timing chest so I'm still baffled.
Not just me then! As my post above, if my bike wet sumps its harder to spin on the kickstart and it might smoke out of the exhaust a bit (but not unless half the oil tank is in the sump) but I don’t get oil out the breather, and I don’t understand why others do experience that, obviously it happens, just why *dunno*
So wet sumping doesn’t bother me at all…..no need to get an SRM pump, or drain it before using it….
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Hi mate as iv said i don't think my problem is necessarily caused by wet sumping.
Undoubtedly my bike does suffer from wet sumping if left a few weeks without being started she will fire up but im greeted with a brilliant smoke screen that eventually clears as the sump contents get returned to the tank. my recent problem oil being forced from the breather occurs even if the sump has been "manually" drained Pryor to starting and riding??
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I'm still really confused must of the advice points to poor scavenging and poor return resulting in excess oil in the crank cases. My return is very strong seems almost too much it really is returning under pressure it is leaving the return pipe and hitting the opposite side of the tank under pressure
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Trust me I was the maker of the thread confused, baffled and covered in oil and my return was excellent to the tank but I still had the same problem. I have not read all the comments but from what I have read it might be the ball in the scavenge pipe sticking. I think the mag change is a red herring its more likely that it stood for a while that has caused it.
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is the return in the tank going at a full 1/8th inch diameter flow and hitting the back of the tank or a thin jet like there is a restriction
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hi again many thanks, the return to the tank is the full flow and still hitting the other side of the tank, i cant work out where that much oil is coming from assuming the return has twice the capacity as the feed ?
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G'day Andy.
Just wondering. Is that the original oil tank? If so has the return stand pipe been altered? Could the hole be smaller than original?
Cheers
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hi again many thanks, the return to the tank is the full flow and still hitting the other side of the tank, i cant work out where that much oil is coming from assuming the return has twice the capacity as the feed ?
From memory the width of the return gears is only 30% bigger than the feed.
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That sounds about right, I rebuilt my pump recently (lapped the joints faces) and while there is a size difference its not massive. The return oil is aerated (and a bit hotter). Since fitting an return filter I've noticed it makes the return flow more continuous.
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At 5000 engine rpm, Supply side = 1.20 lpm, Scavenge side = 1.67 lpm.
Can show more details if needed.
Col