oil pressure relief system

What sender did you use and how did you place it? Picture, maybe?

Just like to clarify the oil pump system on the Commando , in a nut shell the oil pump supply is produced by a gear pump this is a posative displacement pump EG, for every rotation of the engine the pump rotates more revs more oil less revs less oil . The subject of pressure is produced by the resistance against that oil flow all things being equal you do not require a relief valve , but in the event the supply passages become blocked the relief prevents the positive displacement pump blowing up like a ballon and bursting the weakest point . About the relief valve it is only a crude check valve therefore it is also flow concious . When the system pressure rises above the pre set spring value it vents . The initial cracking pressure is greater then the open vent pressure . Hence direct acting relief' s have this characteristic as opposed to a balanced pilot opperated relief valve which remains constant against flow variations . The fitted relief valve is quite adequete for the engine set up . As mentioned by others the relief does not increase oil pressure and flow . Resistance to flow creates pressure , the relief is for protection only . So by externaly adjusting the spring value or with internal shims you gain nothing only a higher relief setting if the flow becomes restricted . Hope this makes sense I have tried to simplify the explanation for the general public . Regards oil type and viscosities that is another story , I prefer the straight oil grades . The lubrication while important for wearing parts is not very technical crude but efective not rocket science . Hope this clears up any conjecture , Norton Dave .

Here is a simple hook up to a mechanical pressure guage. It's just a T going straight to the guage and the side going to the double banjo.

I'm one of the obsessive people who likes to monitor engine oil pressure and since my 70 didn't even have an idiot light I set out to install a gauge. I used the left side rocker arm as a feed source. What I discovered is that on start up the oil pressure would peg my 0-100 psi gauge and the second time I started the engine it over stressed the gauge and ruined it (it would no longer return to 0 psi ). I disassembled the relief valve, cleaned it up, replaced the spring and bought a few shims from Old Britts. After a bit of experimentation, I now run the motor with one shim. On startup the pressure goes to about 80psi for about 20 seconds then settles back to about 40-60. I am glad that I installed the gauge because I would never have found this out otherwise. Over 100 psi is not good on anything inside the motor.

the relief valve is easy to take off and inspect.

BTW I don't know whether having a crankcase with oil from wet sumping has anything to do with this start up oil pressure issue but my bike does wetsump and I am too lazy to drain it before each ride. If my luck holds that will probably tear something up as well!

I had much the same experience. Years ago I acquired a 1972 Commando that had sat indoors for some time. I rebuilt the engine, but neglected to inspect the OPRV. I had an oil pressure gauge installed. Upon start up the 100 psi gauge was pegged. I don't recall the exact numbers, but when I checked oil pressure with a hand held gauge with a 0-300 psi scale, IIRC the pressure was somewhere in the neighborhood of 200 psi. Once I cleaned the rusted OPRV the pressure with cold oil was around 60 psi at fast idle.

Like RennieK says, no gauge, no way to discover the malfunctioning OPRV. Neither will an idiot light let you know of this problem. As I understand it, excessive oil pressure is a no-no for plain bearings. I'm certain someone here can tell us why excessive oil pressure is bad.

L.A.B. said:

Why do you think the head is being over oiled?

There may be other reasons why the head is over oiling, such as the rocker spindles fitted with the flats facing in the wrong direction, a blocked oil drain gallery or problems with the inlet valve stem oil seals.

pvisseriii said:

Alright, LAB, it's good to see we're back on the program

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Also the wrong union bolts with too big a hole for the oil system.
Incidentally, if you have a blocked oil pressure valve on a Commando, with the black plastic rocker feed pipe, this pipe will blow off its connection.

Excessive oil pressure can also invert the lip of the crankshaft oil seal.

JimC said:

What sender did you use and how did you place it? Picture, maybe?

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Well, I used a 1941-1984 HD oil pressure switch from Drag Specialties part # DS-272158 for $11.95 also J&P cycles sells one too # 740-468 for $13.99 it has a 3 pound pressure minimum to turn the light off. One end is 1/8 npt and the other is 10-32 for wire hook up. What I did was unhooked the warning light assimilator and used the white wire that went to the warning red lamp in the head light extended it down to the timing cover. If you have a stock black rocker feed line like I do you will need an old banjo off of a broken rocker feed line as thats what I used to make my adapter next you need a brass 1/8 npt coupling I then silver soldered one end of the coupling to the old banjo I removed from an old feed line I then got a double old style banjo bolt from Old Britts that they sell to put their oil pressure gauge on. Along with three Alum washers. I put the assembled sender and banjo right in the connection behind the timing cover and the sender tucks back towards the trans / engine cradle and is hardly noticeable when finished The whole thing cost under $40.00 to do and works great. I put one on My sons 850 to but it had the braided over head line so his cost more to do as I had to buy a new style stainless banjo and a new style double banjo bolt with washers from Old Britts. I think each of those were around $20.00 each but still all went together the same other wise. If you still want a picture I can take one for you but I'm not home right now but can later and if something isn't clear just pm me or ask and will try an answer your question.

Thanks. I get the picture.

L.A.B. said:

Excessive oil pressure can also invert the lip of the crankshaft oil seal.

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Stole my thunder. We did the blown crank seal due to excessive pressure once on the 750 Norton ultra short stroke.

A Norton wet sump should not have an impact on oil feed pressure unless the tank feeding the pump is empty.

As for the excessive pressure to plain bearings being bad, I can see the unneccessary power (wasted), additional pumping heat (shear) to the oil due to higher pressures and flows, and excessive flow (that) must be returned to the tank and that is being slung around the internals; actual detriment to the plain bearings due to excessive pressure is a question beyond me. I suppose if there were a condition where the flow through the plain bearing upset the dynamic/hydraulic wedge that there could be a problem but I am just speculating here.

On the Norton twin, oil pressure is more less self metering and is gouverned by engine speed, oil viscosity and state of wear of the plain bearings and feed pump.

Knowing the oil pressure is a good thing but keep in mind that considerable pressure is generated at high speeds due to centrifugal forces. With an 89mm stroke crank spinning at say 6,000 rpm, the little 44.5 mm long column of oil (drilled oil gallery) from the centerline of the crankshaft to the centerline of the rod journal adds considerable pressure since it is behaving like a centrifugal pump. I did the math once. This may all be a bit academic for the every day rider but I thought I would blurt it out there.

I just disassembled the assembly and found no shims .
Guess ill hook up a gauge of some type and gets some shims for it .

SRM Engineering make a nice stainless version, set at 50 psi I believe.

http://www.srmclassicbikes.com/catalogu ... duct_id=73

750nort said:

I just disassembled the assembly and found no shims.

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It might not need any. Adding shims is only likely to increase the OPRV blow-off pressure when the oil is cold.

If you are concerned about the integrity of the unit, a Pressure Relief Valve Piston and spring will run you about $15 or at least just the spring for $2.50. These springs can and will lose their gumption over time. I have alsoreplaced the detent spring on the bottom of the gearbox with great success when I was jumping out of first under load. They do go bad.

pvisseriii said:

These springs can and will lose their gumption over time. I have alsoreplaced the detent spring on the bottom of the gearbox with great success when I was jumping out of first under load. They do go bad.

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Do you mean to say "Spring Has Sprung"

Thanks to all for the info