Pressure Release Valve

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I was wondering do u add or remove shims to decrease the pressure the valve relases at? and wot is the correct pressure. and does anyone have a pressure tester i can borrow?
 

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You would need to remove shims to *decrease* pressure. The relief valve operating pressure is 45-55 psi, which is normally achieved with 0-2 shims fitted in the relief valve.
 
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It might be worth mentioning that pressure is, I'm sure, set hot and at 3000+rpm
 

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Cash,

If the relief valve is set to open at a certain figure, in this case between 45-55 psi, then I would expect it to operate at that pressure regardless of either oil temperature or revs?

No set RPM or engine oil temperatures are given for checking pump pressure in any manual that I am aware of, although if you could say where you found this info I would be grateful?
 
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Yes I agree when setting up the pressure relief valve using a thin fluid (I'm not sure Norton would have used air), or a pump with a low flow rate, ie a hand pump. However, thick cold oil supplied through an engine oil pump is another matter. The relief valve may well be fully open but can't dump the excess thick oil quickly enough to lower the system pressure below that set by the relief valve until the oil heats up and thins.

Think back to the days when Minis etc had oil pressure gauges. A Mini relief valve was set for 60psi, when starting cold the oil pressure would shoot up past 75psi and a cooper oil pump would push it past 90psi, while at tick-over you'd see 50psi+.

A hot motor would only reach and hold 60psi at any thing over say 2000rpm, at tick-over the pressure would drop to 20 to 25psi.

Stick an oil gauge on your Commando and I'm sure you'll see the same effect

I was worried that Black and Gold Comando might be reading a gauge fitted to his bike while running cold and then reduce the pressure relief valve to suit, not a good thing perhaps.
If he uses your method I can't see a problem. I've used a grease gun fitted with a gauge and filled with engine oil before.
 

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cash said:
Think back to the days when Minis etc had oil pressure gauges. A Mini relief valve was set for 60psi, when starting cold the oil pressure would shoot up past 75psi and a cooper oil pump would push it past 90psi, while at tick-over you'd see 50psi+.

You appear to assume that all pressure relief valves are ineffective (to a certain degree?) on the basis of one particular type fitted to an engine that has (as far as I can tell) no particular design parallels with the Norton twin engine?

Stick an oil gauge on your Commando and I'm sure you'll see the same effect

I have stuck an oil gauge on a Commando, and no I haven't seen the same effect, even with stone cold SAE 50 monograde and a freshly lapped pump!
 
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Hey Guys,

I don't have anyting to contribute to this hot/cold debate - but I do find it informative to hear your postitons/reasoning.

Thanks and keep it up! 8)

Phil
 
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I'm no fluid dynamics expert but here goes.
Given you use the same hole and same volume of fluid a thinner fluid will pass through that hole in a shorter time at the same temperature. That's how viscosity numbers are worked out. I think its something like, it takes 50 seconds for a measured volume of 50 oil to pass through, and 20 seconds for a 20 oil.
The Norton valve is a spring loaded piston that when compressed uncovers a ring of holes. (I think that's right there's that many variants). As those holes begin to open the hot thinner oil flows faster than the thicker cold oil. And as flow and pressure go hand in hand the higher easier flow causes a pressure drop. To get the same flow of thicker oil through the relief valve holes, the piston has to be compressed further and to do that a higher pressure is achieved.

As you can clearly tell I'm not too good at explanations. If you do a trawl the web you'll probably find something better and clearer.

Apparently the works Commandos on the Island would lose all oil pressure due to heat without detriment.

I use now semi synthetic 20/50 and before that a good 20/50. I have always seen a pressure change with temperature on my Commandos and many others, but I can't ever remember any of them using 50 oil. Do you only use 50 oil? perhaps its the perfect balance for the Norton r/v.
 

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cash said:
The Norton valve is a spring loaded piston that when compressed uncovers a ring of holes. (I think that's right there's that many variants). As those holes begin to open the hot thinner oil flows faster than the thicker cold oil. And as flow and pressure go hand in hand the higher easier flow causes a pressure drop. To get the same flow of thicker oil through the relief valve holes, the piston has to be compressed further and to do that a higher pressure is achieved.

Yes I would agree there could be *some* variation between hot and cold relief pressure, but from my own experience this does not appear to be anywhere near as great a difference as you would have us believe, also the Commando oil pump system not appearing to have any great over-supply capacity in the first place?
Yes I would also expect the indicated pressure to drop as the engine oil got hot, but as a result of the pressure dropping in the system rather than due to the relief valve operating at a lower pressure as you said yourself:
Apparently the works Commandos on the Island would lose all oil pressure due to heat without detriment.
But that (logically?) being due to the lack of pressure in the system and nothing to do with the relief valve I would think? *Pressure* of course, is seen to be the Holy Grail which it isn't really, as flow is just as important, and again from your own words this would appear to be be true?
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cash said:
I use now semi synthetic 20/50 and before that a good 20/50. I have always seen a pressure change with temperature on my Commandos and many others, but I can't ever remember any of them using 50 oil. Do you only use 50 oil? perhaps its the perfect balance for the Norton r/v.

Oil Types !!

This really brings us onto a completely different subject, and one that has been discussed exhaustively here (and elsewhere) and there are widely differing opinions as to which is better and as yet there appears to be no definitive answer.
Mono-grade oil (SAE 30-40-50) was the factory specified engine oil, although they also considered use of multi-grade oil acceptable, monograde was the factory 'recommended' oil, this specific recommendation occurring quite late on, and wasn't something left over from an earlier period as the following quote from 1973 service release N3/59 shows:

Quote:
-----------------------------------------------------------
"Recommended Engine Lubricants

All Commando

Worldwide (General Distribution)

Important amendments to all previously issued engine lubricant recommendations have now been confirmed by the Norton Development Department (see also Service Release N3/47 May '73).

H.D. SAE40 Mono-grade oils meeting A.P.I. service SE or SD performance level now form the preferred engine lubricant recommendations for both current and previous 750/850 models.

(SAE 30 equivalents for ambients below 32°F. (0°C.)

(SAE 50 equivalents for ambients above 90°F. (32°C.)

The previously recommended Multi-Grade lubricants continue with full approval for use, but it must be noted that all future recommendation charts in Rider and Workshop Manuals, and other Service publications will indicate H.D. 40 Mono-grade oils (A.P.I. SD or SE service rating) as the prime engine lubricant recommendations."
-------------------------------------------------

Various noted experts and engine builders recommend monograde oils should be used (I believe using a multi-grade oil in a *Norvil built engine will invalidate the warranty).

*Norvil recommend monograde oil:
http://www.norvilmotorcycle.co.uk/techtalk27.htm

-----------------------------------------------------
And I'm not saying that everyone should rush to change to a monograde oil, only that it is a point for discussion, modern multigrade types may be a better option than monograde was thirty-years ago (although of course modern monograde oil is likely to be better too???)
 
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Yep! I agree with most of what you say.
To go right back to my first comment.
I was taught to do all oil pressure checks etc on a motor and it's lubricant at working temperature. I cannot for the life of me see anything wrong with that.
For sure on a fresh motor etc, the relief pressure needs looking and better too if it can be set remotely. As when cold that's when excessive pressure can arise and do a lot of damage. In the Commando's case it could blow the crank feed lip seal.
 

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cash said:
I was taught to do all oil pressure checks etc on a motor and it's lubricant at working temperature. I cannot for the life of me see anything wrong with that.


I don't necessarily disagree, but you would seem to have missed the point of what I actually said, that I *personally* did not notice any great variation between the COLD oil pressure and the HOT oil pressure readings (as I recall) the cold pressure *not* appearing to rise considerably because of the thicker oil or because of any apparent shortcomings of the relief valve that I was aware of at that time, and there would appear to be no set oil temperature or revs quoted anywhere in any factory service literature (that I'm aware of) to measure the oil pressure at? Obviously when I did this check it was some time ago and I took no notes or performed any oil temperature readings to compare with the pressure readings (perhaps if I'd known then, that I'd be discussing it now I would have done!). A job to do next year then, possibly?
______________________________________


You said:"
It might be worth mentioning that pressure is, I'm sure, set hot and at 3000+rpm

I asked:
No set RPM or engine oil temperatures are given for checking pump pressure in any manual that I am aware of, although if you could say where you found this info I would be grateful?

Your later reply mentioned some figures for a Mini engine, which as far as I can see is hardly a similar design at all?
 
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The Mini relief valve does indeed differ in design but is common to most car engines of that era and for all I know that still might be the case. As for its dump efficiency I cannot comment other than it will have to accommodate a much higher flow rate. The similarity of course is it's basically a spring and piston, the difference being it uses a conical seat on the piston head.

I used the Mini A Series as an example because it's a motor I have a lot of experience of. And deluxe Minis had an oil gauge, and most people will have driven a Mini - Hmmm! over here and my age group, I suppose, bad example perhaps.
 
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Pressure relief valve failure

How do these valves fail? Do they usually get stuck open and therefore you lose all pressure? Do they just leak by and show less pressure? Or What? Thanks Curious Commando with low oil pressure syndrome
 
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I personally have never had the experience of relief valve failure. I have heard of springs going soft, and pistons sticking probably due to contaminated oil.
How low is the motor's oil pressure?
 
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Pressure relief valve

Max 20 revving well then dies off to a few psi at idle. Sometimes it will jump up and drop off quickly when revved. Very frothy return which makes me want to replace the hoses just to make sure it is not sucking air somehow. Happy New Year all
 
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Doesn't sound good at all.

Some frothing is expected as the return side of the pump has a greater capacity than the delivery.
What grade of oil are you using and does the oil tank level drop on start up?

Assuming you're not using a thin modern oil.

First off check the gauge is reading correctly.

Check the feed line is clear and free of kinks, and the oil tank gauze filter is clean

Remove the relief valve, check or replace the spring, check the piston moves freely and do a blow off test as LAB describes.

If you find nothing wrong you'll have to check the oil pump it's gasket and the two other seals. It's an easy task and there is loads of info on what to look for and do. I would pull the pump drive pinion off the pump to check the drive key hasn't failed, and to ensure a previous owner hasn't driven the pump shaft and key through the pump head when it was last stripped. It leaves a nice little groove in the bore and a nice leak point. Replace both seals and the pump gasket on rebuild. Take care to get the lip seal fitted in the timing side the right way round ie garter spring inside the hole. Oh! if the Commando is a Mk3 check the non return valve is free and intact.
It might be an idea to replace the timing side joint with a new one and fit it dry. There is a feed drilling there but I can't for the life of me remember what it does. I'll have to read the book.

If the pump checks out OK, well I'm sorry to say the problem's with the crank and the big end bearings.
Never the less, a Happy New Year to you and all things can only get better.
 

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cash said:
It might be an idea to replace the timing side joint with a new one and fit it dry. There is a feed drilling there but I can't for the life of me remember what it does. I'll have to read the book.

Cash,

The timing cover to crankcase drilling is the gallery for recirculating the excess oil from the relief valve back to the inlet side of the oil pump, as the excess oil doesn't merely drain to the sump.

The 850 MkIII pressure relief system being different to all earlier Commandos in that the timing cover does not have the drilling (although the crankcase does so that timing covers [or crankcases] can be interchanged) and does not recirculate the blown-off oil from the relief valve back to the pump inlet, but vents it into the timing chest as extra timing gear lubrication.

I did wonder if this recirculation of excess oil on non-MkIII types (or at least those that do not have a MkIII timing cover fitted) could partly explain why oil pressure could rise higher than the relief valve setting with a cold engine? As the venting of this relief valve oil could *possibly* be restricted by the gravity feed from the oil tank to a certain extent or maybe even due to the restriction of the narrow gallery drilling itself?

Because the oil gallery connects to the feed oil supply this can be a source of draining-down, (these days what is commonly referred to as 'wet-sumping' although of course that is really something different) as any leakage at the timing cover/crankcase joint face or a sticking relief valve (except those with 850 MkIII timing covers) can allow the oil from the tank an alternative path to the sump rather than draining through the oil pump itself.

Rollingm hasn't said if the valve has been stripped, cleaned and inspected?
Or if the pump has been serviced (lapped) or not?
And I would consider that trying to identify any sort of pressure problem without first ensuring the pump itself is working efficiently is a waste of time, as that should be the base line from which to work (in my opinion).
 
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LAB,
Not knowing how competent a spanner man Rollingm is, or the history of what had been done before I wrote the list in order of the simplest to get at and do before pulling the timing side. It would be a bit of a bummer if the gauge was duff. Fell for that one years ago and still get embarrassed.

Section C22 of the NVT workshop manual for the Mk3 850 states " Oil escaping from the valve returns to the feed side of the pump."
I knew there was a difference but could not remember the detail. As you said the Mk3 timing side cover isn't drilled, but I was unsure if my old Mk1's cover was.
 

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cash said:
Section C22 of the NVT workshop manual for the Mk3 850 states " Oil escaping from the valve returns to the feed side of the pump."
I knew there was a difference but could not remember the detail. As you said the Mk3 timing side cover isn't drilled, but I was unsure if my old Mk1's cover was.

Yes indeed, even the factory manuals aren't always 100% correct!
And I had struck out that sentence in my own MkIII manual a long while ago (and there's another error on the next page etc...! ), as it appears the text had just been copied from previous model manuals without being corrected.

The earlier Dominators relief valve vents to the timing case, so I'm not sure if the very early Commandos did as well....possibly? But not as late as 850 MkI (if you meant '850' MkI?) but of course the camshaft points timing covers are interchangeable.
 
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My 850 had a sudden drop in oil pressure again. This is the second time over many thousands of miles that the pressure dropped in the same way. Was 60 cold, 40 at 3K rpm, 20 at idle now after last ride 40 cold, 10-20 at rpm 0 at idle. Frothy oil returning to hold a good level, does not drain the tank just off the dipstick overnight. I have lapped the pump at least 3 times. It has been 2000 miles since the last time this happened All seals etc were replaced but no sign of gasket/seal failure that would cause this. A new oil pressure guage too. The pump was as snug as I dared lap it. I have used a 20-50 like Spectro for 20K since it's first bore job 20 over. Runs good and quiet but I basically have only run it to long enough to check the pressure after emptying the oil tank to inspect the screen, hoses etc new oil and filter etc Someone suggested I was'nt lapping the pump to a snug enough state so come spring when my hands thaw out from changing the clutch on my R1100GS I will delve into it again Thanks for all your suggestions
 
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