Where's my oil pressure??

Hi guys. I had a problem with low oil pressure on my new-to-me 71 Roadster, so I went in and did the following: checked gauge by inflating rocker oil line - indicated same as my regulator gauge; checked anti-wetsumping check valve for sticking (not) - reinstalled in (same) correct orientation; blew out oil passages in timing cover; replaced crank oil seal (garter facing cover) and snap ring; removed pump and lapped body and end plate surfaces (there was wear on the brass plate) - gear teeth mostly OK, but I carefully filed off a couple of small burrs - reassembled (with same mesh pattern) clearance on pressure side was about .002" - turned a little more easily dry than manual specified; replaced a couple of dodgy oil pump screws; replaced conical seal; used a carefully trimmed paper gasket on the crankcase interface - no shims under the conical washer; filled pump with oil; torqued mounting nuts to spec; reinstalled timing cover with some temporary long screws to assure crank seal not damaged; clearance between cover and gasket about .010 - .015" with hand pressure; torqued timing cover screws to spec; no shims under relief valve cap; primed oil line between anti-wetsumping valve and pump; primed line to O.P. gauge (patiently); filled oil tank (20W50 VR-1).

When I ran the engine I had 45 psi cold on the gauge, dropping to around 30 psi at 50mph or so warm, and about 10 psi at idle. I took the bike out two or three times over several days, riding it only a 4 or 5 miles each time. The oil pressure looked good, and I figured I had solved my problem. Was anticipating adding a shim to the relief valve to see how much that would up the cold pressure. THEN - Friday evening I took it out again (no change yet to relief valve), and after 6 or 8 miles, I glanced down at the gauge, doing about 45 mph, and it showed 20 psi. A half mile later it was down to 10 psi. I watched as it slowly sank to zero over a stretch of about 200 yards - at which point I pulled over and stopped. Oil (and some bubbles) in the tank, no oil trail, no evident external leaks. After a half hour to cool, cranked it up - no joy on the gauge. So I called a buddy to come get me.

Yesterday I pulled the timing cover off (glad that I hadn't used compound on the cover side). The conical seal looked good - evidently compressed, but not over compressed. The crank seal looked good. The two screws I could get to on the pump end plate were tight (and no I had not used threadlocker). The nuts holding the pump on were tight.

At this point, I haven't pulled the pump off yet - I guess it's possible the shaft broke - but before I do that, I thought I'd ask you guys: WHERE THE HECK DID MY OIL PRESSURE GO?????

LIkely just a warmer day and longer ride to thin oil till no-show on gauge. Best check that oil is spraying back into oil tank on blip ups, if so then likely all is well and just normal oil gauge reading for a Commando at speed. Norton used to install oil gauges until the many freaked out riders caused Norton to remove gauges to solve the worrying by owners like you.

Forget the gauge, look in the oil tank to see if returning, like hobot says, things may be working just fine, just British pressure.

Dave
69S

Check the pressure relief valve. Maybe stuck or bad spring.

SRM sell a nice stainless pressure relief valve set at 50 psi. Is the oil gauge your using a good quality item and do you have access to another to fit and compare?

Concur with Hobot and Dave; if you have oil dumping into the tank, forget about it. If you want to do an additional check, with the bike hot and running, crack the fitting at the rocker and see that oil oozes out. I'm sure it will...

An oil pressure gauge on a Commando is not a confidence inspiring thing,although I think they are a good idea. I'm not quite able to see the oil return in the tank while I'm riding. Its quite normal for the gauge to have little or no deflection at idle with hot oil. 10 psi/1000 rpm is pretty much rule of thumb under normal temperatures. During hot conditions pressure will drop below this rule of thumb figure. The oil pressure relief valve only relieves pressure. Adding or subtracting shims or changing springs will not increase the pump output. The only time it is open is at startup with cold oil.

MexicoMike said:

Concur with Hobot and Dave; if you have oil dumping into the tank, forget about it. If you want to do an additional check, with the bike hot and running, crack the fitting at the rocker and see that oil oozes out. I'm sure it will...

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I kinda gotta dissagree with this. There's 2 circuits. 1 feeds the crank, mains and what not and the other feeds the head and related items. Free flowing to the tank just mean the pump return oil from the sump.
This is all well and good but pressure is needed feed the head and related vital components.
Kartisle, loosen the left fitting at the head and see if it makes a mess. The greater the mess the better the pressure.

Thanks for all the responses. I'm debating whether to reassemble and check for good oil flow, or to pull the pump and continue lapping until I have zero end play. It occurs to me that maybe the initial pressure I had cold was limited not by the relief valve but by the viscous flow through that end play - in which case the set point of the relief valve could well be above 45 psi. If I add shims and the initial pressure does not go up, that's what that would mean. Or I could just continue lapping the pump body and get it over with.

A couple of other questions: Has anybody come up with a clever way to mount a pressure gauge closer to the pump discharge? Does anybody know at what pressure the crank oil seal will blow out? That was part of my previous problem, due to a damaged seal, I think....

I've read someplace that non-synthetic multigrade oils don't do to well in aircooled engines. The hotspots can change 20/50wt to 20wt in less than 1000mi by breaking down the esters they use to make 20wt behave like 50wt when hot. How old's the oil?

I read someplace else that on a Commando the only bearing that needs any kind of pressure at all is the big-end rod bearing and it doesn't need much. All it needs is for the pump to present the oil to the orifice on the journal. The crank does the rest. It's an oscillating pump. I don't think the 30psi from the pump would even begin to handle the pressures involved.

Maybe a plain 'idiot light' would be better than a gauge. You start your bike and and the light goes out. You know your anti-sump valve isn't jammed and you're good to go.

Try straight 50W and see if you have pressure. I've seen charts where the 20W50 gets pretty thin at high temps. So far I use straight 50 until I have an issue.

Dave
69S

kartiste said:

Thanks for all the responses. I'm debating whether to reassemble and check for good oil flow, or to pull the pump and continue lapping until I have zero end play. It occurs to me that maybe the initial pressure I had cold was limited not by the relief valve but by the viscous flow through that end play - in which case the set point of the relief valve could well be above 45 psi. If I add shims and the initial pressure does not go up, that's what that would mean. Or I could just continue lapping the pump body and get it over with.

A couple of other questions: Has anybody come up with a clever way to mount a pressure gauge closer to the pump discharge? Does anybody know at what pressure the crank oil seal will blow out? That was part of my previous problem, due to a damaged seal, I think....

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Lapping the faces of the pump is 1 part of the problem. The other is the gears and seal points of the pump( the surface that the gear turn about). If you have gouges and marks on these curved surfaces then there is not much you can do. I found a good pump on ebay and although it was for an atlas, it was perfect in these regards. This was basically a new pump for $20.00. Do not let the fact that if it is an atlas pump it won't work. Other than the machined angle for clearance, they are identical.


The other thing is that crank seals blow out from excess crank pressure not excess oil pressure. A whole other can of worms. You wouldn't have a late 71 or 72 by chance, would you?

bpatton said:

How old's the oil?

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It's new.

Also, it looks to me like I could relocate my present gauge feed connection - with longer hose - from the banjo on the head to the banjo on the timing cover. Is there any reason this not the standard practice?

occurs to me that maybe the initial pressure I had cold was limited not by the relief valve but by the viscous flow through that end play - in which case the set point of the relief valve could well be above 45 psi.

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Bingo a bit of old Norton lore and factual wisdom is now yours.

If you read the appropriate section in the Service Notes you'll find the opinion that use of such a gauge is somewhere between a bad and terrible idea. Not only is it useless once the motor is warmed up, because most of the oil from the pump is doing its work on the bottom end and only a trickle is coming up to the rockers. If it breaks, you might not notice until you've lost your top end.

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Crank/cover oil seals can not be blown out of their seat by a Norton oil pump with such easy exit of oil into the engine, UNless its a defective seal still being sold here and there but I don't know which or how to tell till too late.

Most tap pressure at the head but should read the same as a Tee in at the pump bypass. i'd prefer to get the worst news first so will put my gauge on rocker spindle.

I think you are now wasting time fussing with the supply side of oil pressure as its internal engine clearances that determine what PSI seen on the fly. Some see 50's at 70 mph, others nothing at 55 mph. Can try spring shims and see.

hobot said:

I think you are now wasting time fussing with the supply side of oil pressure...

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For some strange reason, I'm visualizing an oncologist opening up the patient, taking a long look, and then sewing the patient back up again...

Yep. surgery on people or Commandos is too often unproductive wasted effort to operator and more stress to patient left with same issues plus scars and a bill.

pvisseriii said:

Lapping the faces of the pump is 1 part of the problem. The other is the gears and seal points of the pump( the surface that the gear turn about). If you have gouges and marks on these curved surfaces then there is not much you can do. I found a good pump on ebay and although it was for an atlas, it was perfect in these regards.

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Mine looked decent. But thanks for the tip - maybe I'll look for a deal and prep a replacement unit.

pvisseriii said:

The other thing is that crank seals blow out from excess crank pressure not excess oil pressure. A whole other can of worms. You wouldn't have a late 71 or 72 by chance, would you?

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The crank seal is of course weak in containing pressure from the crankcase side, but even though mine is the one with the timed aperture breather, the crank seal did blow toward the engine.

The crank seal is of course weak in containing pressure from the crankcase side, but even though mine is the one with the timed aperture breather, the crank seal did blow toward the engine.

kartiste

Posts: 10
Joined: Mon Oct 12, 2009 8:16 pm

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Not so sure what you mean by "blow toward the engine". Before you start replacing crankcase seals, I suggest you read some of the posts concerning PCV valves. If you prefer a Commando that keeps its oil on the inside rather than the outside, a PCV valve is a must.

My mate bought his first Commando a 750, the motor had just been rebuilt and had similar low oil pressure. It ran for a year like that, eventually it nipped and bent a rod. After his own rebuild the oil pressure was no better and fitted a new oil pump. The pressure improved, 75psi cold, and running hot 45 to 50psi and tickover 15 to 20 psi. He gave the old pump to me and I found the oil pump short spindle was missing. :shock:

I have seen more than once where a PO has punched the pump drive pinion off the pump spindle driving it through the top cap and broaching a deep groove along the bore with the key.

I'm not saying this is your problem but I do feel the pressure is too low.

Cash

pvisseriii said:

MexicoMike said:

Concur with Hobot and Dave; if you have oil dumping into the tank, forget about it. If you want to do an additional check, with the bike hot and running, crack the fitting at the rocker and see that oil oozes out. I'm sure it will...

Click to expand...

I kinda gotta dissagree with this. There's 2 circuits. 1 feeds the crank, mains and what not and the other feeds the head and related items.

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However, both "circuits" originate from the same common source - the timing cover oil gallery, so any reduction in oil pressure or flow is likely to affect both circuits.