Oil Pressure @ rebuilt engine

`Had the `71/750 engine rebuilt over the winter: new rings, bearings/superblends, rebalanced crank, overhauled the head/valves/guides, etc, etc, and have 850 miles on it ...now a running high-zinc conventional 20/50 after break-in. (I removed the old (non-regulated) oil cooler off as part of the larger bike rebuild at the same time. ) Prior to this, the right cylinder had begun burning through about a cup of oil every 100 miles... probably valve guides.

Now runs/performs well, no smoke or oil-burning/oil-loss (also etc, etc.). Does NOT wet sump even after two weeks of idleness/recovering from minor abdomonal surgery before I could start it again. I therefore assume the oil pump/gears/plates assembly is reasonably "tight."

But....

I've always had a Sun oil pressure gauge that I mounted way back in`73 picking off the banjo bolt in the head which feeds the rockers. Before the rebuild, pressure with 20/50 GTX was at least 35-38psi @ 3,500 RPM/hot, and 20-ish psi @ idle.

NOW the indicated oil pressure using that same 20/50 dino oil is ~18-19 psi @ 4,000 RPM/hot, and only 6-7 psi idle/hot. Oil temp in the tank/hot is 210+-ish (no oil cooler). I'm going to pull/replace the oil pressure gauge/pick-off line tomorrow to double-check that I don't have a bad instrument (even though I don't think that's the problem).

Any other thoughts/ideas as to either the pressure, or the "don't-worry-about-it-because-it's-oil-flow-that counts" school of thought?

Hello MEHAVY, I think that as you said, substitution of your oil pressure gauge is a good starting point.

I would make sure that the rubber oil seal on the end of the oil pump spigot is in place, and you could always check that the crank shaft oil seal in the timing case hasn't deformed?

On my Commando, on cold, the oil pressure shoots up towards 90/100 psi on fairly low revs (less than 2500) before rapidly settling down to over 10 psi per 1,000 rpm, so at 3,000 rpm would read around the 40/45 psi area, and this would be with "normal running temp oil," i.e. going around town, riding at no more than 50/60 mph

But as soon as it starts working hard, cruising at 70 mph plus for any length of time, the oil pressure will drop down to less than 10 psi per 1,000 rpm, and will read as low as 30 psi at 4,000 rpm. When it starts to do this, I slow down a bit and up comes the oil pressure.

If correct, yours does sound quite low.

Hope this helps.

Reggie said:

On my Commando, on cold, the oil pressure shoots up towards 90/100 psi on fairly low revs (less than 2500)

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Are you sure the OPRV hasn't stuck in the closed position?

LAB wrote;

Are you sure the OPRV hasn't stuck in the closed position?

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I'm reasonably sure it's not stuck, although I assume that you are referring to the fact that it should release at 55psi.
I am using a straight 50 oil which I think may be partly responsible. As I said, (within 2 minutes) the pressure is down around the 60 psi mark as the oil warms up. I'll maybe just re-check it (the OPRV), but it has always been like this since I was last looking at it, and it wasn't stuck then.

MEHAVY, just another thought, did you fit the paper gasket behind the oil pump?

Reggie said:

I'm reasonably sure it's not stuck, although I assume that you are referring to the fact that it should release at 55psi.
I am using a straight 50 oil which I think may be partly responsible. As I said, (within 2 minutes) the pressure is down around the 60 psi mark as the oil warms up.

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I know when I re-shimmed my OPRV after lapping the pump, the oil pressure would quickly reach the "pre-set" relief pressure, but it wouldn't rise above that pressure-even when cold, and that was also using SAE 50 mono. oil if I remember correctly.

I posted recently on a similar phenomenon. Pre-reringing, my motor was pretty consistently at 40 PSI at 3k RPMS or higher - a few pounds flux depending on ambient temperatures.

After a new set of rings, which have the motor feeling very healthy, same conditions yield 30-35 PSI. (Cold start up pressures haven't changed that I can see - this seems strictly to be a warm engine phenomenon).

Only other difference is I'm using dino oil instead of syn (both 20W-50) for break-in. So possibly the dino oil isn't holding viscosity as well as the syn?

Quote from the late John Hudson,
Mention of pressure brings me to another point-the fitting of oil pressure gauges. On the Commando (and for similar
reasons. most bikes) an oil pressure gauge is more of a liability than an asset. It is of necessity, fitted on the feed side
where any failure of pipe or gauge is disastrous to engine and rider--it’s touch and go whether the engine seizes
before or after you fall off with oil on the back wheel. On the Commando this failure could be caused by engine
vibration in the same way that early rocker pipes failed. (We’re coming to that.) The other reason that a pressure
gauge isn’t much good is really twofold. At high speeds and high oil temperatures the pressure can drop to nothing
on the gauge because the pump can hardly keep up with the rate the stuff is flying out of the big ends. The
centrifugal force can keep the pressure at the big ends above the danger point, so there’s no real panic--but the gauge
would inspire you with horror. Then of course if you did seize an oil pump by the time you noticed that the pressure
had dropped the big ends would have gone (. . . through the hole in the crankcase, with average N.O.C. luck!). If you
want an interesting gauge to frighten yourself with, but, which is inherently safer and can give useful information, fit
an oil temperature gauge in the oil tank. Let me know what it reads as you change into top for the Mountain Mile on
both the fourth or fifth lap! The latest Racing Nortons (we can’t call them J.P. Nortons any more as they’ve stopped
the bikes from smoking) had a new type of oil pump-I wonder if this is because the ordinary pump can’t keep up?

September 98 Classic Bike issue has 21 mods listed by Les Emery to keep your Commando on the road. One of those was the enlarging of the oil galleries in the crank case to improve flow to the oil pump. Les stated no larger than 1/4 was recommended. Maybe this could improve oil pressure?? Has anyone heard or done this before?
Foxy
P.S. I wonder what size oil galleries a Steve maney case has??

Yes I have drilled 3 half inch holes to vent pressure pulses better to
the extra volume of the TS case and then from case out via
Combat breather hose.
Beware that lowest hole will set the oil level in TS case,
must be enough to splash and carry oil to all components.

More venting or lower pressure only helps much at rpms
the crank is staring jump rope.
It should not affect oil pressure, just less oil weeps at speed.

hobot

Thanks guys.

I pulled off the right side head banjo connector to the oil gauge line and got pretty good volume coming straight out of the head upon engine start-up, ...but it was being shoved out rather than really spurting across the driveway like it should have. Once installed, the new gauge said the same thing, ...about 1/2 normal oil pressure.

Looks like it's time to pull the right side off and go after both the oil pump and crank shaft seals. :cry:

The lower pressure could be due to higher oil temp since you removed the oil cooler. Conventional multigrade oil can loose the high temp viscosity very quickly. It gets that 50wt in a 20/50wt by using esters that are consumed leaving you with 20wt oil. If you want to to use a multigrade oil you might want to switch to synthetic. Why did you remove the oilcooler?

Why use 50 grade? Must create a lot of engine drag.
Using 10-40 quite happily myself.

Removing the oil cooler upon overhauling the bike was at the recommendation of the engine builder (who is truly a Norton guru w/o parallel). The localized hill`n dale riding I'm doing now is a far cry from when I crossed the Mojave in July/August`75 and first installed the cooler. So I said, "...OK, let's ride w/o it for awhile."

The *pre* rebuild oil pressure would read 60+ PSI upon cold/start and drop to to 40 PSI when fully hot.

The *after* rebuild oil pressure won't go higher than 36-38 PSI at most on cold/startup, and then drops 20 PSI from that when hot. (I even tossed 6oz of STP in there to stiffen the 20/50 up, but saw little effect once hot.)

`Definitely a pressure leak in the system/seals somewhere.

MEHAVEY you might have a good inspection inside your oilpump. Recently I bought a new 'genuine Andover' pump, after starting up the engine there was only 5 psi pressure but good returnflow inside the oiltank. At last I took the new pump apart to find out both pressure bores were machined 0.008" (0.20mm) to deep! The clearance of the gears and pumpbody should be as close to nothing to produce maximum pressure so I grinded the body and rebuilt the pump. No need to say this completelly solved my pressure problem.

Every Norton would benefit from an oil cooler. I'd be interested to hear the Norton guru's w/o parallel explanation.

Some of the advice from so called Norton experts contradict common sense. The common refrain seems to be, "If it were needed Norton would of built it that way".

JimC said:

The common refrain seems to be, "If it were needed Norton would of built it that way".

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That's a pretty bold and uninformed statement.

I question the need, for most riders, for an oil cooler. It takes a long time for the oil to get to proper (hot) temperature.
In fact, my usual 15 mile loop morning ride still results in oil that is just nicely hot.
In 1972 I rode my stock Combat on a 5000 mile trip around the United States with no cooler, running all day at 75mph in 90 degree temps with no issues. I can't remember now if it came fitted with an oil filter got that matter.
Commandos seem to handle sustained riding withou oil coolers just fine. Of course, it is just good sense to change out the oil frequently anyway, I do every 1000 miles, castro 20-50 GTX is still pretty cheap for three quarts!

Stick a thermometer in your oil tank when running 75mph @ 90°F. Then ask an oil engineer what happens to oil at that temperature. That's what I did and I've run an oil cooler ever since. It is important to have a thermostatic bypass. Too cold oil is harmful, also.

JimC said:

Stick a thermometer in your oil tank when running 75mph @ 90°F. Then ask an oil engineer what happens to oil at that temperature. That's what I did and I've run an oil cooler ever since.

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Ditch that cooler and simply use a good synthetic oil (withstands much higher temperature).

I do run Redline 20-50.