Engine breathing (Oil drip)

[bsa-bill]

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

[brackenfel]

My engine (and bike) is late 1961, DA10-14xxx , 4-Spring clutch etc... I don't thinnk this breather is standard..

Adrian

[BSA_54A10]

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.

[Brian]

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.

[bsa-bill]

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.

[BSA_54A10]

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.

[trevinoz]

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.

[Brian]

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?

[trevinoz]

That's what I think, Brian.
                                  Trev.

[muskrat]

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

[bsa-bill]

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    )

[lawnmowerman]

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

[muskrat]

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

[trevinoz]

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.

[Brian]

Here are a couple of photos that show the oil breather hole.