Ammeter or oil pressure gauge for petrol tank?

Hi Alan,

You don't mention what model the bike is. If it is an early Model 7 there was an oil pressure gauge fitted into the left side hole on the top of the petrol tank from 1949 -1952

Originally a 0-160psi. Eureka gauge made by Tomey.

If you have a Model 7,  the drive side crankcase will be stamped with a 12 prior to the engine no.

I can send a photo of how to mount the gauge if required.

I saw an oil pressure gauge on one of the early Model 7 bikes, and was surprised that it read to 160lb. So how high does it go on start-up? What is the regulated pressure supposed to be?

Some Commando owners (especially in the USA) seem to like fitting gauges.  They report numbers like 75 cold. But much less when hot. Norton famously removed the gauge when panicked owners reported close to zero at high revs when hot, when centrifugal effects in the crank caused more suction than the oil delivery pressure.

Check the search function on here for others' experiences.

You'd want a generous safety margin on a gauge.

Hi Alan,

Sorry it has taken a few days to get back to you as my tank was safely stored away as it is plated and painted ready to fit. Can't be too careful. 

I have removed the gauge to show the fitting arrangement. 

If you want any specific measurements just let me know.

Hi Alan,

Here's the measurements that will assist.

If there are any parts you want more specific detailed information on please let me know.

Hi Alan, I've added a couple of photos to clarify the mounting of the take off unit.

The photo taken from the 1949/50 Model 7 parts book shows the set up for the mounting.

Relevant part numbers are 75, 76 & 77 and are shown just below the pressure release valve in the rear of the timing cover. The tapping is 5/16" x 22 t.p.i (BSF). The bolt used to attach the rocker feed union is the same on cast iron heads used on these early model 7's.

Several years ago you could get lengths of fine copper pipe with the 1/8" BSP union attached. I don't know if they are still available.

Any other questions just let me know.

Ian, thanks for all the great info on oil pressure gauge plumbing and take-off.

I see you indicate feed is taken at banjo bolt from below pressure release unit.

I know this is used for feed to rocker box but wondering if I need to add  a T added to the rocker box feed line with one going to pressure gauge and the other to rockers?

Have I missed something in the notes above?

Regards

Peter Cooper

That tapped hole in the timing cover was used on early Model 7 machines for the oil pressure gauge, and on mid-1960s and later bikes for the pressure-fed valve rockers, which had the six-start pump drive worms. If I remember correctly, early 650 SS machines, and early Atlas had the 3-start oiling system. It is likely that the 6-start system was developed due to the demands of hot 750cc machines operating in hot climes of the USA. Early machines should not be converted to pressure fed rockers unless the lubrication system is altered to the full specification of the later oil system.  Besides the six-start pump worms and the plain rocker spindles, there are a lot of detail changes, which were done for a reason.  With those later bikes, you could fit a T-piece in the oil line so that the pressure gauge gets a feed along with the rocker spindles.

If you have an earlier bike, and feel that you are not getting enough oil to the rocker spindles, the factory recommended modification was to fit a Jubilee or Navigator oil return tank union.  This is identical to the heavyweight twin tank union, except that the drilling through the centre for the oil to pass through is slightly smaller, thus forcing more of the oil returning to the tank to go upstairs.  This modification is mentioned in PL Garratt's workshop manual of circa 1958.  Should you wish to do this mod, but do not have a lightweight twin tank union to hand, there is a solution - cut a steel disc smaller than the threads on the union, drill a suitable sized hole in it, and silver-solder to the end of the standard tank union.  My Model 88 has one modified in this way, and it's been there a long time.

If you feel that your bike just needs more oil flow, then get a Commando oil pump, and fit it with the 3-start pump worm as standard for your earlier bike.  The Commando pump has wider pressure and scavenge pinions, and so it will give more big end oil pressure and it will scavenge more efficiently.  Should you wish to purchase a new pump, this is your only choice - the earlier pump is not offered......

Hi Peter,

Here's the setup on my plunger Model 7. The oil line is not in it's actual position so you can see the set up. Rocker feed is on the return union in the oil tank.