Atlas/Dommie Oil Mist Scrubber

I have owned my Atlas for over 50 years, and for most of that time I have been firmly convinced the "froth tower" was of little or no effectiveness in controlling oil mist escaping from the oil tank . Thus, having the tank off the machine for a new powder coat finish, I resolved not to let another half century pass without having a look inside to see what Norton was doing to control oil mist. And so, I cut off the cap at the top of the tower and had a look inside. Here is what I found:

The timed breather hose attaches to the lower tube which enters the tower at the base, and then turns 90 degrees downward, terminating at the roof level of the oil tank. Between the lower tube, and the upper vent tube, there is 1 1/2 inches of air....gravity is the principal of operation, but 1 1/2 inch elevation change just will not do the job.

Now I had to close up the tower, and still desired to control oil mist. My solution was to fabricate a scrubber cartridge that is inserted into the tower, and secured and made oil tight by a nut or cap.

The cartridge is as below, and will be explained further below.



First is was necessary to Dremel grind all remnants of the old tower cap and weld, making the inside of the tower tube smooth and burr free.

Not having the machine tools necessary to cut threads on the exterior of the tower tube, which would also require a nut or cap to be fabricated, I sought someway to apply threads to the mouth of the froth tower tube. I found that a 1 inch conduit compression fitting would slip over the tube.




I cut off the lower part off the fitting, leaving only the threaded ring for the mating compression nut.



The threaded ring is made of pot metal and can be soldered with special low temperature alloy solder, temperature indicating flux, and sufficient skill. Lacking all of the above, I elected to JB Weld the ring to the tower tube. Besides, I feared application of heat to the thin ring would warp it, making the nut bind.

Hint: Apply grease to the threads of the ring, in case you inadvertently get JBW on the threads....that way you can get the JBW off without chasing the threads with a thread file, as I had to do. Get the ring square to the tower tube.



The scrubber cartridge is fabricated as follows:



Item 1) is a 10-32 x 1 1/2 machine screw, 2) #10 flat washer, 3) 1 inch Dia. discs cut from 3M stripper pads, 3A) has a notch to clear the exit port, 4) 10 - 32 nut, 5), 6) gasket ...preferably a very compliant material like cork or neoprene, 7) 1 1/4 OD fender washer. Blue locktite the nuts.

Slip the cartridge into the tower tube, and secure with the compression nut. The nut fits between the frame and tool tray with close but sufficient clearance.



The cartridge can be easily removed every other oil change and rinsed with solvent. Don't be too critical of the paint on the frame...that is original paint with 50 years and 85K miles of use.

How effective is the scrubber? I have not run it yet, but close mesh filters have been used to scrub oil mist in automotive applications for the last century. I am sure it will be more effective than the "air" filter employed by the boys at Plumstead Road.

Next task: clean up the tank and prep for powder coat. I plan to coat the nut and top washer as well (protecting the threads with high temp. tape).

Slick

Update: 7.14.17 - I have changed the media to fine mesh and added one more media disc. The extra disc requires the media to be compressed. I do not think this increases the back pressure significantly.

Update: 7.4.20 - Removed the cartridge recently. Found the scubber media saturated with oil, showing that it is effective in removing mist from the vapor. Also, I am not getting the oil mist deposit on my rear wheel.

Comments and questions are welcome.
PM me: texasSlick

Good mod there. I know that there used to be a rule of thumb that requires an oil tank on a Norton-like motor to have 130% of the oil capacity to allow for the froth returned to the tank.
cheers
wakeup

Slick, I am curious as to how well the scrubber worked out??

Stephen Hill

Stephen Hill said:

Slick, I am curious as to how well the scrubber worked out??

Stephen Hill

Click to expand...

The simple answer is "I still do not know how effective the mod described above is, I am close to starting up after extensive refreshments/restorations."

The long answer is:

Very early in my ownership of the Atlas, I began fighting oil smears on the engine cases in the area of the primary drive, and I surmised it was coming from the breather tube off the oil tank. The tube terminated in the chain guard near the gearbox, and the idea was the oil mist would lube the chain. The chain speed is too fast for that, and the oil was being slung forward landing on the engine cases and dripping after that.

My first mod was to fabricate a shield which I fastened to the inside (engine/gearbox side) of the inner chain case, similar to that on Cdo inner chain cases. This kept the engine cases clean, but I still had the drips, .... at least the drips were localized.

I next tried several types of scrubbers in the breather tube coming off the timed breather port, between the port and the oil tank. The first type was a fuel filter with a hose barb on each end, with the barbs fitted vertically and tucked into the space between the oil tank and battery box. This was an improvement .... there was less oil drips.

I found the best scrubber was to replace the fuel filter with an inverted bottle (I am guessing it was about 4 Oz. volume). The bottle cap was a screw lid into which I soldered two tubes, one just inside the lid, the other extending near the bottle bottom (which is on top when inverted). The bottle was packed with steel wool. The tube coming off the timed breather entered the short tube, and oil/air passed thru the steel wool with air exiting the long tube and then to the oil tank, while coalesced oil returned to the sump. This worked very well ... I estimate it trapped 80-90% of the oil ... there was always a drip hanging on my shield anytime I ran my finger over the edge.

I always was concerned all this extra plumbing would increase the sump pressures and contribute to oil leaks everywhere else. I cannot say for sure this proved to be the case, but I have always fought "oil sweating" out the timing cover gasket, etc.

The Atlas is near to be cranked up with the following improvements (I hope) with respect to breather and oil mist control:

I have installed an XS reed valve at the timed port, replacing the 90 degree elbow with the valve, and running a tube to the oil tank off the XS valve. Yes, I know the timed port should do the same thing as the XS valve, but I think this will be an improvement. If the oil sweating stops, I'll take that as proof, but I plan to make some pressure measurements with and without the XS valve.

Next, there is the scrubber mod described above. This does not have the surface area of the steel wool in a bottle, but it has the advantage that I am only trying to remove oil mist from air leaving the oil tank, rather than entering. Granted, the air volume entering and leaving is the same, but the mist density may be less leaving. I have the option to vary the type of media from which to make the discs. I will post results ASAP.

While this mod may not be better than the bottle, one thing IS certain, it HAS to be better than nothing.

Slick

When you say "3M stripper pads," you can't possibly mean the stuff that's impregnated with abrasive!

Triton Thrasher said:

When you say "3M stripper pads," you can't possibly mean the stuff that's impregnated with abrasive!

Click to expand...

No. These pads are for stripping paint. That is, to clean up the residue after applying a chemical stripper. They are much like the green pads used to scrub pots, but stiffer, thicker, and more porous. They come in several grades, like sandpaper does, ... I started with the coarsest grade as a first go.

Slick

I use the 3M type pad material for a external tank breather gauze