The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Brian on 03.12. 2007 00:48

Title: Engine breathing (Oil drip)
Post by: Brian on 03.12. 2007 00:48
I was wondering if anyone has modified their engine breathers and what they have done. I know some put on a inlet rocker cover with a vent hose. The problem I would like to overcome is when you pull up after a ride there is always a drop of oil on the ground from the breather tube. What I had in mind was to run the breather tube into the primary case and vent the primary case to atmosphere. I like to try and get my bikes totally oil tight and this has been annoying me for quite some time, any ideas?    Brian.
Title: Re: Engine breathing
Post by: a10gf on 03.12. 2007 01:59
Here it is! A container with a pipe from the breather, a small fueltap at the bottom, emptied when nobody is there to watch :O)

Title: Re: Engine breathing
Post by: Brian on 03.12. 2007 03:37
Thats a good idea and is what I will do for now while I think about it. At this stage I am still considering the into the primary case option.
Title: Re: Engine breathing
Post by: LJ. on 03.12. 2007 09:15

I had only recently fitted a breather tube from the crankcase as I could feel quite a strong breathing there while the engine was running and I was suspicious that alot of oily mist was covering the underside and behind the primary. Since fitting the tube, although quite dry, it still breaths quite forcibly. I'm wondering if there should be an odd drop of oil from the tube after switch off, or do I have a very well set up breathing system? It seems that BSA didn't put in any hose as such and just alllowed the engine to breathe straight out the side. Could your problem Brian, be the thickness of the oil??

I dont think rocker inspection covers with breathers are a good idea or draining into the primary. I'm sure that BSA would have done that if there was any real benefit.
Title: Re: Engine breathing
Post by: groily on 03.12. 2007 10:01
I note on my engine someone has attempted the rocker cover breather mod - and then blanked it off. I assume because it turned out not to work, to leak, or whatever. Certainly it's not the ideal place. I think a collector system is probably best, as what comes out is actually supposed to, within reason, and pressurising other places can't really help much and maybe could make more leaks? Groily
Title: Re: Engine breathing
Post by: Brian on 03.12. 2007 11:04
Going by the picture in the parts manual the original breather tube BSA fitted appears to have gone straight back to the sprocket, possibly so the odd drip went onto the chain. This is not a big problem but I dont like the odd drip, especially when I pull up on someones new driveway and tell them how british bikes can be oiltight !!!
Title: Re: Engine breathing
Post by: a10gf on 03.12. 2007 13:00
Out from the shop in 1955 or whatever date they were oiltight ! I see on my bike (and others) the leaks were bad gaskets, uneven tightening of screws, and deterioration of contact surfaces (f.ex somebody in the past enjoyed splitting the crankcase with a screwdriver + hammer etc). I had some damaged surfaces built up again with auminium welding and then I filed\polished to get the original contact back, = 99% oiltight with an ok gasket. The very small emanations I've got is no more than can be wiped away now and then or when cleaning the bike.

The breather is another story, on my bike there is quite a lot oil\condesation mix coming out, due to all kinds of yet unknown reasons, but the little container fixes it in practice. If you fit some oil-container, remember to have some top hole on it to let any pressure out. btw I enjoy parking next to other british bikes (look, no oil drips ! ).
Title: Re: Engine breathing
Post by: RichardL on 03.12. 2007 15:46
If I am following correctly, the little oil container is for catching drips coming from the oil tank vent. Is this correct? Apparently, the issue raised by LJ regarding mist from the crankase breather collecting behind the primary is not helped by the drip collector. The recent disassembly of my engine was done after very few miles, but the mess behind the primary was significant. Perhaps this was due to other problems that led to the disassembly, however, if that was normal for such low mileage, I want to consider a fix. Has anywone tried something like tapping the breather port and installing a fitting and tube to route the mist down to the street rather than spraying it on the crankcase? 

Richard
Title: Re: Engine breathing
Post by: a10gf on 03.12. 2007 16:06
Quote
If I am following correctly, the little oil container is for catching drips coming from the oil tank vent

There should be no possibility for spill or pressure from the oil tank vent. It's the engine breather. My theory, with an engine in perfect condition everywhere, the oil amount from the breather will be very low. As wear escalates, the crank pressurising from valve guides, cylinders and things I have not thought about, may force more oil out the breather.

So rather than doing the whole engine prematurely because of some oildrops, it's collected with a tube from breather to container. Emptied now and then, quite a lot in there sometimes, water(condensation)\oil mix.
Title: Re: Engine breathing
Post by: RichardL on 03.12. 2007 17:31
Erling, et al,

I think I know why I am confused. The breather path on earlier A10's, like on the plunger (I think) is different from that used later, where the outlet path passes under the camshaft oil gallery and exits behind the primary case. (I learned this during a previous thread where we were discussing the "unusual" cam pinion gear.) Am I correct that that is not the path used for your bike and that the breather output is somewhere toward the right side rather than the left?  If so, by what means is the tube to the trap connected to the breather output?

Richard
Title: Re: Engine breathing
Post by: a10gf on 03.12. 2007 20:51
Hi Richard. On the plunger the breather pipe exits near the rearchain gear sprocket, which is the left hand side of the engine. Suppose it's meant to drip on the chain. There is a piece of plastic tubing that fit a protrubing breather outpout pipe, routed to the extra oil container. Not my idea all this, it was like this when I got the bike, found out it was worth keeping.

E.
Title: Re: Engine breathing (Oil drip)
Post by: LJ. on 03.12. 2007 22:13
Ah! It's off to the parts book to see if I have always been missing a breather output tube on the swing-arm.

I could not see any mention of one in my books... There was nothing on my crankcase. (1961 Swingarm)
all there was was a hole.... I put in a nice fitting brass tube with a rubber hose led down to the bottom of frame.
Title: Re: Engine breathing (Oil drip)
Post by: a10gf on 03.12. 2007 23:08
In the 49 to 53 engine chart the breather pipe is there, pnr. 67-922.
Is it not supposed to be there on later models? Maybe dislodged by a loose chain or something ?
Title: Re: Engine breathing (Oil drip)
Post by: Brian on 04.12. 2007 01:09
The swingarm models do have a tube, same part no as the plunger models. They are a press fit in the case but I always put a drop of loctite on them as well. In my experience with A10's they seem to pump a bit of oil out when you first put the motor together but after about 1000 miles it settles down to just the odd drop which is what I am trying to overcome. I have decided to put a catch bottle on for now and in the future will either run into the primary case or back to the oil tank. At least we have created some discussion for the Forum which is always good.        Brian.
Title: Re: Engine breathing (Oil drip)
Post by: a10gf on 04.12. 2007 01:56
I would not recycle the expelled oil, can contain condensation \ water.
Title: Re: Engine breathing (Oil drip)
Post by: LJ. on 04.12. 2007 09:51
Is the brass tube just a press fit in the hole?

Can be, Yes! If you can find the perfect fitting tube. I remember looking around for the ideal fitting brass tube and found that a good model shop will sell this. I seem to remember that the hole was 8mm in diameter, I maybe wrong as brain cells struggle to hold data nowadays. It seems that BSA may well had fitted these tubes as Brian suggests but with heat and vibration they would eventually be prone to falling out. However a good rubber hose fixed with a jubilee clip and securing to the frame should ensure it stays put.

I found it interesting during my research on this, that by looking at crank cases on ebay and at autojumbles, a number of people had tried to overcome the problem of the tube slipping. I had seen a number of punch marks around the hole and various cements and glues etc. This might all seem very petty but I do agree with Brian about parking up on someones neat and tidy paved drive way. Plus the old BSA/Oil leak jokes get a little tiresome after a while.
Title: Re: Engine breathing (Oil drip)
Post by: dpaddock on 08.12. 2007 01:09
Ah, the eternal breather problem!
The root cause is blowby gases from the combustion chambers during the power strokes. This phenomenon is multiplied by the 180-degree crank arrangement, whereby both pistons pressurize the crankcase in unison. More importantly is the fact that the crankcase has very little volume to absorb the pressure rise from blowby, and when the breather valve opens the crankcase pressure is initially quite high - especially in "non-new" engines.
A simple fix would be to increase the case volume by adding a bottle of sufficient volume to the crankcase to reduce the pressure rise at the breather valve. Wet sump engines have large crankcase volumes which greatly minimize this problem which, when coupled with multiple cylinders, create blowby pressures hardly much more than atmospheric.
Routing the engine breather outlet to the primary drive case is a step in the right direction as long as one drains the case regularly. I did this on a racing Gold Star with good effect, at least sufficient to complete a race card.
In any case, make sure there are no external openings to the engine that could increase the amount of gases the breather has to handle.
Title: Re: Engine breathing (Oil drip)
Post by: Brian on 08.12. 2007 03:38
Hi dpaddock, I put a small bottle on the breather to see how much oil was coming out and after 200 miles I had about half a teaspoon 3 or 4 ml so its not a major problem, just an annoying one. What I had in mind for the primary case was to run the breather into the case and then put another breather in the case to vent it. All this would not be seen [forgot to say this is on the swing arm model] The small amount would only require the case to be checked for level every thousand mile or so, maybe less. Its a simple job on the s/arm models as they have a level pipe as part of the drain. I am in Australia so the climate is warmer and there is no condensation to deal with. My plunger had the same problem for about the first 1000 miles but once it had settled down it only very rarely drops any oil. This one has only done 700 miles so far and will hopefully improve as time goes on. I hope to ride both bikes so it will be interesting to see which one ends up being my favorite.     Brian.
Title: Re: Engine breathing (Oil drip)
Post by: LJ. on 08.12. 2007 09:59

With the amount of oil loss that Brian reports, then I don't see any problem in draining into the Primary case. But for anyone thinking of going down this route having a considerable amount of oil loss then I think problems can arise within the clutch arrangement. Whilst an excessive amount of oil is good for the clutch bearings etc, I don't think it would be long before a slipping clutch problem arises. Anyone with a slack primary chain would be amazed to see how much splash there is in the case, especially if the level is above the reccomended hight.

By the way Brian... I have seen small breather holes in the clutch spring adjusting screw, thats if you have that sort of primary cover.

(Have a good weekend everyone! Safe riding out there.)
Title: Re: Engine breathing (Oil drip)
Post by: dpaddock on 10.12. 2007 02:46
First of all, let me correct my post: I meant 360-degree crank, not 180-degree.
Anyway, there's no sense adding a bottle to the primary case to reduce excessive crankcase pressure. That phenomenon occurs in the crankcase, not the primary case.
In a perfect engine there would be no blowby and no external openings to the outside. Thus, there would be no need for breathing. If you visualize this, you can make your non-ideal engine less leaky - button it up and seal the combustion chambers from the crankcase.
Title: Re: Engine breathing (Oil drip)
Post by: RichardL on 29.12. 2007 15:58
Gents,

I am returning to this topic in reponse to Pim's question asking, "...what this 'breather' is everyone is talking about?"

In this thread, we've talked a lot about the oil drip from the breather, but I don't think we answered the question as to why the breather  is really there and what the timing implies. Pim's question made me think a little harder about this. With quite a bit more more than a little repect for dpaddock, I'd like to suggest a different reason than blow-by or pressurization by the pistons. While it is true that pressure in the crankcase due to blowby gets out through the breather, the breather is not timed for this, as there are two ignitions for each breath from the breather.  With regard to pressure from the pistons when they come down, that pressure is relieved when they go back up.

Even though I wanted to, I did not try to calculate the pistons' position when the breather port is open. That would be interesting, but take too much time, also, my crankcase is now out for machine work. If someone knows, please share.

Anyway, my opinion is that the breather is serving two purposes, the most important being to achieve near-atmospheric pressure in the crankcase so that oil can be pumped in and sucked out. In a worn engine with enough blowby to presurize the crankcase, oil could probabaly, be sucked out, but it might not get back in. The second purpose is the exhausting of blowby, for the reason mentioned. While there may be something to the timing of the breather, I don't see it and I think it may not matter. Instead, I think it is just a convenience of the  architecture of the crankcase.

The vent on the oil tank serves a similar purpose as the breather (except for the blowby issue) in that it allows oil to be sucked out and pumped back. 

As always, I am quite interested in contrary and abundant more expert opinion.

Richard

Title: Re: Engine breathing (Oil drip)
Post by: RichardL on 29.12. 2007 16:37
OK, I'm going to argue with myself. If all they wanted was atmospheric pressure, they could have just had a hole into the crankcase and forgotten about the rotating breather. So, now I think It must inhale on every other upstroke to prevent excessive oil (mist or otherwise) from being blown out on the down stroke.

Richard
Title: Re: Engine breathing (Oil drip)
Post by: RichardL on 29.12. 2007 23:18
In honor of being completely obsessed, the arguement with myself continues (since no one else has told me I am wrong). Since my engine is disassembled, I decided to take the gears in question, the breather and the inside timing cover and look at the relationship of the breather hole with respect to TDC. My crankshaft is off to machining, so I had to look at the parts book to see the relationship of the woodruff key with the crank journals. From what I can see, the keyway points directly toward the journals. Based on this, and contrary to my previous assumption, it appears that breathing occurs on the downstroke approximately 90 degrees ATDC. To me, the 90 degrees part makes sense, because it should be the point of balance between compression and vacuum in the crankcase. I still like my idea of doing the breathing in the upstroke, but I guess BSA had another idea, yet to be revealed to me.

Richard
Title: Re: Engine breathing (Oil drip)
Post by: Pim on 30.12. 2007 13:02
Sorry for being a complete noob, I understand what the purpose is now, but i can't picture it where this breather is, and where the oil leaks out. In time when the engine will be running I'm likely to find out I guess. But since you have got your engine apart, is it possible cou could take a picture so I can visualise it a bit better? Thank you for the detailed post(s) :)

Pim.
Title: Re: Engine breathing (Oil drip)
Post by: RichardL on 30.12. 2007 15:22
I want to steer all to the following web page and the other pages connected with this one. I just discovered it while searching for breather timing topics. I don't know if some of you have seen this, but it includes the firsthand stories of engineers at BSA. On the page I am providing, Roland Pike describes designing the rotating breather for the Gold Star and discusses its timing. I don't know if breather timing for the Gold Star is similar to A7/10s. If so, I got it wrong. However, in honor of my current obsession, I will be reviewing it again.

http://www.restorenik.com/daytona/RP_chp_23.htm
Title: Re: Engine breathing (Oil drip)
Post by: a10gf on 30.12. 2007 20:27
(off topic)

Pim, don't be sorry, ask for any help and information, and soon you will answer others question. Everyone with an A have had lot's to learn, discover and ask or read about. It will be very interesting to read about your progress on the bike.

e.
Title: Re: Engine breathing (Oil drip)
Post by: Pim on 08.01. 2008 12:36
(also off topic)
Ok:)


Manosound, I'm from the Netherlands (Enschede/Rotterdam)
Title: Re: Engine breathing (Oil drip)
Post by: Rocket Racer on 06.05. 2010 04:46
I was recently reading an article on a racing A10 side car built in NZ in the mid fifties for which the owner had written to BSA due the indifference of his local BSA agent. the owner states David Munro from the technical department at BSA sent him a response dated 17th March 1954 in which he recommended the use of the famous 67-358 cam and a number of other mods including...drilling a new location hole in the mechanical breather to give the thirty degree retard that DM wrote was most important.
Thought you might be interested...
Title: Re: Engine breathing (Oil drip)
Post by: brackenfel on 06.05. 2010 20:16
Brian,
This photo has been on the Forum before but I can't remember how to find it so I'll post it again...
My bike has never been remotely oil tight in the short time I've owned it and it's in bits to try and fix this.. I had a mysterious leak on the primary side - loads of oil dropped but I couldn't see where from.

When I removed the primary cases I found this on the engine block :-
You will see a small brass tube pointing downwards - this had no other hose attached, something I'll rectify on re-assembly and direct it towards the rear chain!
Experts here on the Forum said it was a not uncommon mod, maybe your bike has one too..

HTH,

Adrian

Title: Re: Engine breathing (Oil drip)
Post by: MikeN on 06.05. 2010 23:41

When I removed the primary cases I found this on the engine block :-
You will see a small brass tube pointing downwards - this had no other hose attached, something I'll rectify on re-assembly and direct it towards the rear chain!
Experts here on the Forum said it was a not uncommon mod, maybe your bike has one too..


Er, Yes,Mine has one too.But I think everybody who owns an "A" does. Although your original steel one appears to have been replaced with a shiny brass one. Its originally listed as BSA part number 67-992 "Breather".
MN
Title: Re: Engine breathing (Oil drip)
Post by: bsa-bill on 07.05. 2010 09:36
Don't think any late A10s had this tube, None of the three I have owned have had and it's not listed in my parts book at all
Title: Re: Engine breathing (Oil drip)
Post by: brackenfel on 07.05. 2010 13:03
My engine (and bike) is late 1961, DA10-14xxx , 4-Spring clutch etc... I don't thinnk this breather is standard..

Adrian
Title: Re: Engine breathing (Oil drip)
Post by: BSA_54A10 on 08.05. 2010 01:19
The breather tube was supported by a P clip on the back of the primary cases.
The very first time the primary cover is removed the P clip is either taken off, falls off or is not not bolted back up again.
The weight of the tube eventually causes it to foul on the chain when the chain will shorten it all by itself.
BSA followed the existing theory of the day to create a slight negative crankcase pressure when the engine was running.
And this theory dates from the time before oil seals when slingers were used to stop engine fumes and oil being pumped out  from around every shaft.
The logic behind this was air would be forced into the cases through any holes.
It is only a real problem if the rise and fall of the pistons do not cancel themselves out ( single cylinders , 360 deg twins etc, etc, etc)
No one has really questioned this till receintly when Rex Bunn had a good look at things and has turned most "old theories" on their heads by finding that allowing atmospheric pressure to be drawn in on the up stroke & expelled on the down stroke actually improves the efficiency of the engine .
Through breathing is not new, it was used on a lot of old time racers but not on road models to any extent .
I am not trying to spruke his breathing kits but the theory behind them and some of the findings on the way through were quite interesting particularly on the way rings tend to work much better in one direction than the other, the resonant frequency of flapper type breathers ( as fitted to M & B series BSA's) , response times ( and lag times ) of commercially available one way valves ( PCV valves & Brake valves ) .
His work has caused both HD & Enfield to modify their engine breathing systems and some historic racers have claimed up to 0.5 increase in Hp, better fuel "economy" and less oil consumption.

Now back to reality.
The gasses in your crank are air, fuel & oil droplets ( caused by mechanical splashing inside the cases )
BSA attempted to remove the suspended oil droplets by creating a convoluted path for the exscaping air which would allow the oil droplets to condense and return to the crank. Good idea dosn't work at elevated revolutions.
Remember BSA published an oil consumption of 100 mls of oil per 200 miles for the A7 & A10 and this oil either goes out the pipes or out the breather or in reality out both.
Title: Re: Engine breathing (Oil drip)
Post by: Brian on 08.05. 2010 01:44
Here is a scan out of the parts book for the late models. You can see the breather tube, pt. no. 11167-0922 plus the "P" clip Trevor refers to.

These tubes are almost always missing for the reason Trevor has stated.

What I do is get a piece of copper tube about 2'' long and turn the outer dia so its a snug fit in the cases. Use a bit of loctite retaining compound and tap the tube about 3/4" into the cases and then bend it to point straight down, put a piece of rubber or plastic tube on that and cut it off level with the bottom of the frame. There is plenty of room in front of the sprocket for the tube.
Title: Re: Engine breathing (Oil drip)
Post by: bsa-bill on 08.05. 2010 10:02
Yep  I see it, and it IS in my parts book. goes to prove our (my) eyes see what they're looking for OR NOT.
Title: Re: Engine breathing (Oil drip)
Post by: BSA_54A10 on 08.05. 2010 12:28
Not really trying to be pedantic but you drop the "111" off the part number so it is just 67-0922.

Some one once told me the reason for the 3 digit prefix on the European & General export part numbers but it has long ago fallen out of my numskull.
Title: Re: Engine breathing (Oil drip)
Post by: trevinoz on 08.05. 2010 23:26
As far as I know, the breather tube was never fitted to the swinging arm engine.
I have stripped many of these bikes over 40 plus years and have yet to see one except for those fitted by owners.
The plunger/rigid engine had one.
         Trev.
Title: Re: Engine breathing (Oil drip)
Post by: Brian on 09.05. 2010 01:01
Good point Trev, I always assumed that the tubes had got mangled or gone missing for one reason or another, maybe they were never there?

Title: Re: Engine breathing (Oil drip)
Post by: trevinoz on 09.05. 2010 06:37
That's what I think, Brian.
                                  Trev.
Title: Re: Engine breathing (Oil drip)
Post by: muskrat on 09.05. 2010 08:26
Yep, my 51 A7 didn't have one but the 57 SS that came from Brazil and looked like it had been round the world twice did. Once again learned something here today.
Cheers
Title: Re: Engine breathing (Oil drip)
Post by: bsa-bill on 09.05. 2010 10:01
But it is listed in the S/A A10 parts book although I can't ever recall seeing any evidence of where the screw for the clip would go ( threaded hole ?)
Of course here are mistakes in the parts book ( didn't know Haynes wrote them   *smiley4* )
Title: Re: Engine breathing (Oil drip)
Post by: lawnmowerman on 09.05. 2010 20:45
Hi All

Very interesting thread.
I have just checked my 1959 Super Rocket and although it is difficult to see down behind the chaincase it does not look like I have a breather tube fitted. I pushed a screwdriver down the back where it should be and it all seems smooth. The engine is a DA10R and it has HC stamped below it.
I am a bit confused because I have been looking at earlier threads about wet sumping and people have said that if the oil drains down into the sump and there is too much for the pump to clear on start up, it all ends up on the garage floor. The solution seemed to be removing the sump plug before starting and draining any residual oil. So in my case, if it wet sumps and excess oil is not manually drained off, how does the oil actually get ejected from the sump without a breather tube ? or is it only a problem with pre swinging arm A10s.
The reason I am interested is that I am getting parts together for some mods over next winter. I started a thread a while back regarding anti wet sumping valves with a combined kill switch and I received some excellent advice so I am looking to carry out the following mods:

1.   Oil valve with a combined kill switch from W Dove in Walsall who makes them for AMCs which are notorious for wet sumping. He reckons that it can be adapted to fit our bikes.
2.   Oil pressure gauge mounted between the clocks picking up the oil pressure through a tapped hole in the side of the oil pressure relief valve.
3.   Oil filter mounted in the tool box.
4.   Possibly a Bunn breather kit but I am now a bit confused as to whether the S/A A10s actually vent to atmosphere at the moment being as I do not seem to have the breather tube fitted.

I got a bit lost reading about the timed breather earlier in this thread and I am not sure how it finally finds atmosphere (if at all). If my bike wet sumps, what problems is it likely to cause and how would I even know about it if I have no breather tube to expel the excess oil?

Sorry to be such a nob but I am sure someone here can help remove my confusion.

I think I will go and put a bag of ice on my head now!

Jim

Title: Re: Engine breathing (Oil drip)
Post by: muskrat on 09.05. 2010 22:10
G'day Jim,
              The excess oil from wet sumping finds it's way through the timed breather and out on to the floor.
All of your planed mods have merit, I have done them all. I can't remember which thread I explained my Bunn set up. I cut the timed breather thing just behind the holes and re-fitted it to stop cam shaft end float. Now it has no timing for the breather. Where it exits the cases i fitted a hose fitting and hose for the intake of fresh air. Then put another hose fitting in the inlet valve inspection cover and hose for the exhale breathing. I have a home made oil tank so exhale into that and then another hose to vent the tank. Works very well.
Cheers
Title: Re: Engine breathing (Oil drip)
Post by: trevinoz on 09.05. 2010 22:18
Jim,
            The breather outlet is in the bottom surface of the camshaft tunnel close to the primary case.
It is just a 5/16" hole. [or thereabouts]
                 Trev.
Title: Re: Engine breathing (Oil drip)
Post by: Brian on 10.05. 2010 00:19
Here are a couple of photos that show the oil breather hole.
Title: Re: Engine breathing (Oil drip)
Post by: lawnmowerman on 10.05. 2010 11:29
G'day Muskrat, Trev & Brian

That explains why I could not find the breather pipe - looks like they were trying to save the cost of a bit of tube on the later bikes. I think I will save the Bunn mod until I need to take the chaincase off so I can get to the hole and tap a thread in it to connect a pipe union.

I have found your Bunn thread Muskrat and have saved it for future reference.

Thanks for the help - I can remove the ice bag from my head now! *beer*

Jim