Camshaft breather stationary plate

hello  the camshaft end breather as far as I know is a standard part and had not changed over the years  right up to the commando  and you find this part in the Norton Parts Books over the Years  now for the part numbers T2078 stationary plate cam breather  T2075 rotary plate for camshaft breather  T2108 spring for camshaft breather  these are the 3 main parts for all Dominator twins   including Norton Manxman 650 and Atlas 750 and P11/N15 750 models  ,   YOURS  Anna J

hello   but these parts numbers may of changed with the take over from Plumstead   in 1963 

And I have No information On Plumstead parts , Has I only concentrate on Bracebridge Street motorcycles   so there for do try and get a parts book relative to your motorcycle  see ebay or Norton Owners Club  Shop,     yours   Anna J 

The breather plate did change at some point,presumably to alter the breather timing , I think it was in the 650 time line.  

stationary T2078

rotary breather 24301  1963-1965  = ALL NHT includes 64 650SS

rotary breather 24301  1966-1968  = ALL NHT

24301 all commando thru 20M3

No literature found for 20M3S but is still rotary breather

I have not found much on the stationary plate even though I did replace an atlas one a long time ago. The DPO had tried to remove the drive side cam bush using a hammer and punch through the case hole and cracked the brittle hardened plate.

I am posting the rotary discs despite not knowing (yet) the specific application.

Each disc window is 60 degrees wide.

The two drive tabs are at (CAM+90 deg and -90 deg from cam lobe center) therefore cam and piston TDC.

I knew they changed at some point, How do we find out when?.Apears to be 3 types.Hudson would have memorised the engine nos and part nos!!. He was a one off.

I had one 62 650SS engine without a cam in it and looked to see the black oily breather still in there.

I had to use compressed air to blow it out. My finger could not grab it. Once I saw it, I was stunned to see it is the RED style/spacing.

I was assuming the stationary discs hole position might change as the NHT evolved. It's orientation is based on the dowel pin drilling position. I went to a  52 M7 500, 57 600, the 62 650, 65 20, and 71 20M3S and All the stationary windows are at 2 and 8 oclock.

I will have to calculate the vent timing and see what the possible reasons are for the other two rotating discs.

This anomaly  has  lodged in my brain like an ear worm jingle and woke me up at 4am. I have not found the remembered reference and have looked in all my official reference books. It must be in the  60's John Hudson  engine rebuild article that I have yet to locate.Its just typical of the man  who spent years stripping down  problematic motors all over the uk . His  success in problem solving  using very basic tools he could carry on a bike ,  working in dark sheds,alleys and if lucky a warm kitchen was legendary. His observation skill and encyclopedic memory  was a wonder and I received the full "benefit" when on a train journey  with him. The stuff that no one else knew was his bread and butter.

Sounds like John Hudson and I are similar in some ways. Might have liked to have met him.

If Tomas feels to continue this thread with a bit of research, we might get his question answered.

Some initial data is presented...after a search for rotary PN

D12-934

T2075

24301

Previously shown red/orange/black timing discs, shown against SS cam timing and TDC/BDC reference.

breather opening is .25 square inches when fully aligned

The breather timing was changed in 1962.  I presume that was for the 650ss. possibly from lessons learned from the Manxman ?.

I have been having problems with my Dominator breathing for some time. My article in Roadholder 314 following Tony Ripley's article 'Crankcase - Breather Theory' in Roadholder 302 provides details.

From David's photo above it appears there are essentially two types of rotary breather plate: the red type and the orange/black type. From his graph above the red type appear to be fully open halfway down the downstroke whereas the orange/black type are fully open around BDC. Thus the red type breather will be nearing closed when the pressure is highest (BDC) wheras the orange/black type is fully open. Also similar to the valve overlap concept, the orange/black type will continue venting on the upstroke after BDC until the pressure collapses. Intuitively the orange/black type look like a better prospect. I have the red type fitted to my bike.

The red type is a D12/934 (later changed to T2075) 

The orange/black type is a 24301 

All camshafts appear to have the breather disc driving cut outs inline with the woodruff key slot. My camshaft is a Daytona with QR

The stationary disc T2078 appears to be constant throughout the range and years with the holes being between 12-2 and 6-8 o'clock. 

On the face of it, I think I could improve my situation by installing the 24301 rotating disc. can anyone see a downside to this approach?

Other questions

Is anyone running with the red type (T2705) set up on a pre '63 Dommie with no crankcase oil leaks/breather problems?

Is anyone running a pre '63 Dommie with an orange/black (24301) set up with no crankcase oil leaks/breather problems?

According to my John Hudson Notes, the engine breather timing disc was changed around engine 103749. Well into the Atlas era but before the move to Woolwich.

With the dogs at 6 & 12 o’clock the original port positions were at 3 and 9 o’clock. The later timing with the dogs also at 6 &12 became 10 and 4 o’clock.

There is a big difference in the timing , the only way to compare is to try them out in one engine.  Can't see that happening   any time soon.   I'll bet JH  knows the answer.  Bless him.

John often pointed out that the original Hopwood engine design had far more to the breathing cycles within it than people realized and that messing about with these often caused unwanted side effects. For example the downward movement of the pistons helped to push oil and vapour up the drain tunnels onto the timing cog teeth, gears and chains. As well as oil towards the camshaft followers, lobes and pushrod ends. Owners who drilled or filled these tunnels, moved the breather piping or added a one-way untimed valve could do unintentional internal damage.

He pointed out that on an upward stroke of the pistons, an untimed one-way valve would cause a partial vacuum that actually pulled oil away from the oil pump causing a partial cavitation in the scavenge side. In turn causing the oil pump to run dry on said scavenge side and thus promoting wear to it.