Oil pressure relief valve shims (2008)

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mike916sp

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Anyone know how many shims should be in the above? The Norton parts list states 4 but my bike only has 2 shims in the valve. Looking in the service manual this states the shims were factory set to achive the correct relief pressure but there is no way of knowing if my bike, 1974 Mk 2A 850, is still shimmed as it left the factory.

I have been told that you should have a minimum of 4 to get decent oil pressure. Is this correct and should I fit another 2 shims to make certain the oil pressure is ok?
 
oil pressure

This has been a topic before I think, there seems to be some disagreement,best plan is to give Mick Hemming a call, he is relatively close to you,Mick will give you all of the info. that you will need,he is a terrific fella to deal with. phone:-604 - 638505.
Good luck. James
 
I fell into this trap some time ago thinking the shims produced oil pressure. It was LAB what bailed me out, thanks. Over shimming the spring would only increase the blow off pressure not increase the oil pressure only the pump can do this. I was told that the shims would do the job by an old time mechanic and I believed him. Never made a bit of difference on the gage though. You do not want to increase the blow off pressure without knowing what you have done. If you need more pressure fix the pump.
 
mike916sp said:
Anyone know how many shims should be in the above? The Norton parts list states 4 but my bike only has 2 shims in the valve.
Click to expand...

Please do not make the mistake of assuming you *need* 4 shims because four in number (or five?) were specified?

The shim quantity specified gives you the option to select the correct quantity.
The amount of shims required to set the relief valve at the correct blow-off pressure can be *between* 0 and 5 shims (my '74 parts book says quantity= 5), and generally 0 to 2 shims (with a good spring & piston) will be adequate to set the blow-off pressure to the recommended 45-55 psi.



mike916sp said:
Looking in the service manual this states the shims were factory set to achive the correct relief pressure but there is no way of knowing if my bike, 1974 Mk 2A 850, is still shimmed as it left the factory.
Click to expand...

Maybe it is, and maybe it isn't, set as it left the factory, but this really is of no importance whatsoever, what is important is the oil relief pressure now and of course the actual hot running oil pressure and whether it is adequate or not?

mike916sp said:
I have been told that you should have a minimum of 4 to get decent oil pressure. Is this correct and should I fit another 2 shims to make certain the oil pressure is ok?
Click to expand...

No not really......That is just guessing....and the information you have been given is incorrect as far as I am concerned.

You need to collect some actual hard and fast data.

And the only way to find that would be to fit a test gauge (whether temporary or otherwise) to check the blow-off pressure, which will be the maximum pressure the oil will reach with a cold engine immediately after starting up. As the oil heats up and becomes thinner it escapes out of the bearings more freely and the system pressure drops to a lower pressure level than the relief valve operating pressure because the pumped oil is providing less resistance to the oil pump.

The relief valve should be regarded more as a safety valve that can vent excess pressure out of the system, and not a device for regulating running oil pressure.

Fitting too many shims can increase the cold oil pressure to a point where it can turn the timing cover crank end feed seal inside-out! Which could result in no oil pressure at all!

So first I would try to ascertain if there is indeed a problem that needs fixing?

Before trying to fix something that may not (yet) be broken?
 
Thanks for the information LAB - very well explained.

As I've owned the bike for 2 years now and clocked up some 9000 miles on it with no oil pressure problems I think it is something that I will leave 'as is' :)

I just had the timing cover off to change the timing chain, which had some tight spots, and thought I'd out of interest see how many shims were in the valve and thought it was worth checking if I should have four before refiting the timing cover.
 
I would not however suggest that anyone should totally ignore checking oil pressure at least periodically, using a test gauge like the type sold by RGM Motors, that connects to the existing timing cover banjo rocker feed outlet using a double banjo adaptor bolt so that the rocker feed pipe is left connected during the test, as this could show up engine big-end wear, worn pump, blown crank feed seal or a sticky relief valve etc..
But I do know that members here have expressed mixed feelings about the pros and cons of fitting permanent oil pressure gauges.
 
Hi all - I am working on a pressure relief valve now (on my current project bike), & just for your info this one had 1 shim only... I have no means to check the oil pressure, & am assuming that the orginal setup (1 shim) is OK.

Any comments?
 
The OPRV is for using dead cold oil. It's a blow off Valve. You should be making about 10 lbs of oil pressure per 1000 RPM with hot oil. The only way to know is to check it with a known good gage. Ignorance is bliss. Do what you want you will anyway. But give me a gage. JMO don't take it hard.
This is my set up. there are four pictures just hit the right arrow. http://tinyurl.com/3bl2pz
 
Those are a Boyer wire repair kit. You take the hollow braid from an old cable TV wire solder the connections and shrink tube the units. I have made a few odd tools in my past though.
 
I have some money in the bank that I keep a pretty close check on. I do the same with an oil pressure guage on my Commando. I'd hate to find I'd lost either one.
 
Hi,

this is my first post, (74, 850 Commando, owned since new)

Regarding oil pressure relief valve, I have no shims fitted from new and when I tighten the domed nut by hand the spring offers no resistance.

Is this normal or should I renew the spring? Does anyone know the free length of a new spring? :?
 
Skoti, welcome to the forum.

I think what LAB says is the only real way to go. Get a pressure gauge whether temorary or not, and see what it makes cold and then see if it makes in the region of 10lb per 1000 rpm when hot.

When I was at Mick Hemmings shop last year, he said that he added shims until the free play in the spring was not quite all taken up. In other words, it will still just "rattle" in the housing when shaken. Unscientific, but this is what he advised. The pressure release valve on mine had no shims in it either, but using the above method, I think I put one shim in.

I have just ordered an oil pressure gauge from Old Britts, and am awaiting delivery. 8)
 
Hi Reggie,

thanks for the advice.

Would be interesting to know if the 'Mick Hemmings method' you mention actually works.

Maybe when your new oil pressure guage is fitted you could post the results?

Skoti
 
Hi,

I'ave taken the oil pressure valve apart and can't remember which way round the plunger goes back in!

Does the spring fit inside the plunger?

:?
 
I just rebuilt a 750 Fastback with the Old Britts gage installed. I also had to replace my relief valve when the threads in the timing cover stripped. So with a new "rebuilt" oil pump and good clearances, I had a chance to make adjustments "fetter?" I am using stainless washers for spring tension. It is easy to peg the oil pressure to the head with too many washers. I am now down to two washers and stiil have too much pressure when cold. When hot I now get 10-15 psi to the head at 3,000 rpm. I am going to measure the stack of washers and continue to find the right height that does not give me 80+ psi when cold. When I pull the relief, I lap the copper seal and spray it with copper kote and it seals nicely. The oil pressure gage is the key :D
 
I've just fitted the Old Britts oil pressure gauge.

COLD

1000rpm 95psi
2000rpm100+ psi

HOT
1,100rpm 15psi
2,000rpm 33psi
3,000rpm 55psi
4,000rpm 70psi

Looks like I will have to look at the shimming. I think I have either one or two shims in the pressure release valve.

I am running with SAE 50 at the moment and will soon be changing this for SAE 40. I may see if this alters things at all.
 
Reggie
The first time I removed my timing cover I found the crank oil seal had inverted and pushed part of itself inside out, just as L.A.B. mentioned earlier.
I reassembled and fitted an RGM pressure gauge to the head union. The warm oil pressure was about 100psi at 3000 rpm.
I dismantled the relief valve and found 3 shims inside. I reduced this to one shim and achieved the desired 55 psi @5000 on hot oil. I then removed the complete PR valve and, by shaking it as Mick Hemmings suggests, I could just detect a gentle rattle, signifying that the spring/shim assy was nearly but not quite touching. So Mick must have descovered this and transposed the method so avoiding the need to rig up a gauge.
Obviously a gauge is the most accurate way but the rattle method is also about right.
Dont run too long at your current setting, since there may be a danger of inverting that seal.
 
Reggie said:
When I was at Mick Hemmings shop last year, he said that he added shims until the free play in the spring was not quite all taken up. In other words, it will still just "rattle" in the housing when shaken. Unscientific, but this is what he advised.
Click to expand...

Mick demonstrates that method of setting the relief valve in the NOC Engine Restoration DVD.
 
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