Norton Dominator Model 7

I have had some success with the Norton Dominator Model 7. It now has that new Commando oil pump, Commando pressure relief valve 6 start oil pump drive gears and Comand rubber pump to timing cover seal. The 6 start gears drive the pump twice as fast as the Dominator 3 start gears did.

The Norton manual and Norton forums I have read talk about the oil pressure relief valve being set for 60psi but cold the oil pressure often exceeds 80psi or so. Nobody seemed to question this. This overpressure is what wrecked the Nortons pressure gauge. I have a new 60 psi gauge but would not put it in until this overpressure problem was resolved.

There is a clue in the pressure relief valve setting of 60psi and the actual 80 – 100psi seen at the gauge. So, I had a careful look and measure up of the various galleries in the timing cover and found their cross-sectional area was wildly insufficient to allow enough discharge flow to limit the excess oil pressure. I have never seen anyone talking about this on the Forums.

Yesterday I opened up the oil pressure relief gallery to 5mm in the alloy cover after removing the screw in metal plug. Using a 3mm end mill, I added 3 extra bleed holes to the new Commando relief valve and opened the discharge gallery from it into the timing cover to 6mm.

When refitting the modified Commando oil pressure relief valve I removed the two shims and made sure there was some pipe sealing compound on the threads inside the timing cover. Big possibility of hot oil leaking past the pressure relief valve.

Started the Norton to test my work and now the cold oil pressure is reliably limited to 55psi, even when blipping the throttle. Very happy with that. Next move is to fit a good 60psi gauge and see if the Commando oiling system can help the old Dominator hold proper oil pressure when hot after a long run.

Next move is to take it for an extended run to see if it keeps oil pressure when really hot.

I would post a picture of the bike but can't seem to figure out how? Any tips would be welcome.

If expected pressure is around 50 psi, I’d fit a 100 psi gauge. I think that’s normal practice.

I took the Norton for an extended run. Oil pressure was about 35psi hot at cruising speed and 10psi at a fast idle.

I know that fitting a 100psi gauge is normal practice but it is a work around bodge.

If the expected maximum safe oil pressure is 50psi but climbs when reved or cold then maybe improving the pressure relief system is better than fitting a 100psi gauge. Anyway that is the path I took and a 50psi gauge has better resolution in the critical 25 to 45psi range than a 100psi gauge does.

Gauges are most accurate at around halfway round the scale.

Perfect, makes sense. Thanks for the heads up. Good to know because that puts my 60 psi gauge right on the money at 25-35 psi when the engine is hot. And my improved pressure relief modifications prevent the normal Norton 80 psi or so overpressure when engine is cold from damaging the 60 psi gauge.

Pressures I am hoping to see after a longer ride. (more than 50 miles). So far I have only been about 15 miles in one run. The engine was hot but the oil tank barely warm.

Cold 50 psi .... limited by the modified oil galleries and relief valve. Oil, good quality 20W-50 multigrade.
25-35 psi .... cruising hot. Depending on engine rpm. New Commando oil pump and 6 start oil pump drive gears.
5-10 psi at idle.