Hello, I've dismantled the relief valve on my 1971 750 and there aren't any shims as shown in the parts book. If I push the piston down towards the gauze end of the body till it bottoms out then drop the spring in and screw the cap on the spring rattles up and down when I shake it. I'm guessing I need shims or the spring has sagged out. Should I just buy a new complete valve or spring and shims?
I also noticed what looks like a machined groove running the length of the bore and presume it's to lubricate the piston or prevent hydraulic lock?
Just buy a new one.
Just buy a new one Adam. It sounds like the old one is past it's best. Peace of mind for little money.
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The groove connects the back…
The groove connects the back of the piston to the outlet of the valve, without it full oil pressure could build up behind the piston which would stop it moving.
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Hello Michael, that's…
Hello Michael, that's something I've yet to try. I bought the bike as almost complete. Other than a brief engine start to make sure it ran, that's as far as I got before going front to back checking the condition and serviceability of components and I'm nearly halfway.
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Pressure Valve Springs
At some time in the mid-70s The Norton Factory announced that their PRV springs were being so accurately made that they no longer required shimming up.. So the fix in this case is to purchase and fit a new spring. Not forgetting to remove any shims stuck up inside the piston.
The smart move is to then warm the engine and check the oil pressure. You can buy a gauge that plumbs into the rocker feed on the crankcase for this purpose.
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Thanks Philip, I'll renew…
Thanks Philip, I'll renew the spring then check the pressure once I've finished going through the rest of the bike
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According to the late Mick Hemmings, if there's no rattle when you shake the relief valve then it's probably shimmed too tight.
You could add shims until it stops rattling and then remove one shim at a time until you have a rattle again.
There again someone may come along soon with a more precise technical adjustment method...