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.
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.
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?
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?