Over-excited oil tank breather

Running in can sometimes take longer than we wish , and until there is a good seal you can expect extra blowby to cause heavy breathing . It’s the reason I piped my breather to the oil tank. Now I have no mess under the bike but it’s messy in the oil tank!!.    

Later tanks had a 'froth tower' to reduce/prevent this. Norton knew it was an issue and advised a lower oil level for fast runs!

seem on the ball to me, you will get lots of blow-by with new rings + bores etc. 

On my bike, I have a Commando oil filter plate behind the gearbox between the engine plates, and a 1/4 litre plastic bottle tucked between the gearbox and frame gusset.  The crank case and oil tank breather pipes go into it.  If you can find space for a larger bottle it would be a good idea.  You can put the oil caught in the bottle back in the oil tank, or perhaps on the rear chain.  Much better than spreading the oil on the ground or over your rear tyre.  It means you can monitor how much oil is escaping via the breathers.

My tank (1955) does not have level lines on it, but half way up the tank is minimum, max is 3/4 tank, the extra is frothing space.  In my opinion the tank is too small. 

I need to check just how much oil my bike is using, but the tank was alarmingly empty when I checked during a petrol stop during a run.  It was down to 1/4 full, having been over 3/4 full last time I checked it earlier that day.  Good thing I carry a 2 litre bottle on long runs......

The post 1955 Dominator oil cap is heavily abused by over-tightening. The consequence of this being the top edge of the oil tank filler lip becoming distorted where the ears/tangs of the cap engage. This distortion can be seen by first wetting the lip with a trace of oil and then setting a small sheet of glass on top of the filler lip.  A piece of thick Perspex will do as an alternate. If a continuous ring cannot be seen then the potential for a leak is there. Usually a new gasket will usually do the trick but serious distortion may require some metal working.

Another problem that can occur, in this area, is again due to over-zealous cap turning. The filler lip is held in place on the tank by a folded and pressed internal metal band. This can be manufactured with a gap between the joins or wear and tear can do a similar job. Either way, hot oily vapour just loves these kind of joints and will show itself on the outside of the tank as a thin dribble running down from the cap. A quick fix that did seem to work in the past was to clean the area suspected of leaking and then spread hot Araldite over the seam. A gas torch can be used to warm the Araldite while it is being applied. Do remove the oil tank from the bike first.

The Norton Factory knew they had a excess vapour problem once the 99 engine appeared. Thus the original short pipe, from the back of the engine to the gearbox sprocket, then got hooked up to the oil tank. This works well with half a tank of oil but not with the correct amount. Then the camshaft driven breather disc had its timing changed but this only partially helped. The best solution being the froth tower oil tank fitted to 1962 on Dominators.........unless of course you have splits or distortions as mentioned above.

is for the slimline frame.  Would it fit the narrower wideline? I know I have seen pictures of the froth tower arrangement, but don't know where to find one.

Can you give details of the breather timing, in its early and later form?  If you have a replacement cam, will it have the revised timing? 

A tower can be hard soldered to the tank and some 3/8”. Copper gas pipe unions soldered in . Fumes and oil going in on the lower pipe , fumes going out on the higher and piped to the chain or rear of bike. The only issue can be condensation that can gather in the tank making regular oil changes important,

The froth tower of the slimline oil tank can go into the wide line BUT 2 areas of sorting needed. First the Wideline tool tray becomes an embarrassment, it can be removed and replaced with a Slimline tool tray-same side hole spacing. The slimline oil tank then has a top mounting bracket with nowhere to go!. You can ignore the bracket. BUT then the vibration splits out the bottom of the oil tank, it makes a mess, I know!

directly in front of your rear tyre will make a mess of your trousers as well....

I had a riffle on line, and found a page on Access Norton describing a revised froth tower arrangement:

https://www.accessnorton.com/NortonCommando/atlas-dommie-oil-mist-scrubber.16411/

Just theorizing, but if you mount a slimline oil tank in a wideline, you could use a spacer between the tank's upper mount and the frame's bracket.  No idea how wide that would have to be.

Not a bad idea to cut a hole in the tool tray anyway as they tend to hold water if you ride in the rain.

would have a rising pipe from the engine, a one-way valve, and then a froth pot draining to the oil tank. No timed breather. 

I know that on a Vincent, the breather is timed to open at crank case maximum volume, and close at minimum volume. The timing is easily altered.  People experiment, and say that they get better results when the breather opens at half stroke and closes at half stroke.

But, a one way valve actually works better.

Tony, can you give me details so I can look up that interesting Enfield froth pot?

Paul