Oil pressure relief valve

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Mar 21, 2006
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Has anyone got advice or preferrences as to how to set the oil pressure relief valve (850 Commando Mk1)
I know that the professionals like Mick Hemmings prefer to use the absolute minimum of shims in the valve to reduce the pressure in order to minimise oil leaks, claiming that there is still plenty of flow through the crank.
Far be it for me to question such renowned experts but it does seem a little odd to reduce the overall oil pressure just to minimise oil leaks. I am concerned that the crank and bearings always have good oil flow quantity and pressure. Oil is the most important bearing in the engine.
Factory seem to set these valves with 5 shims between the spring and cup and imply that there is no adjustment needed. The relief pressure is set at about 45 psi.
I guess the only way to check it is to rig up a guage somehow. Any views?
 

L.A.B.

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scim77 said:
Factory seem to set these valves with 5 shims between the spring and cup and imply that there is no adjustment needed. The relief pressure is set at about 45 psi.

The procedure is to select the correct number of shims (0 to 5) to set the relief valve pressure.

I think my (850 MkIII) took one shim to set the pressure around the upper end of the recommended range of 45-55 psi measured with the test gauge fitted (available from RGM Motors UK) to the rocker feed connection (the rocker pipe was also connected during the test).

There were no shims fitted when I dismantled the relief valve for the first time.

I tried two shims but if I remember correctly that gave too much pressure.

And there are no oil leaks!
 
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Mar 21, 2006
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Thanks L.A.B. That sounds like a more logical way to do it. Phone call to RGM required. Cheers.
 
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Mar 21, 2006
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Further to previous posts, I bought an oil pressure gauge from RGM and connected it to the rocker feed banjo on the timing cover. Much to my horror I noted a pressure of over 100 psi at 3000 rpm. Remarkably the engine was still oil-tight even at this excessive pressure.
This explains why, when I was checking inside the timing cover a while ago, I found that the crankshaft oil seal appeared to be distorted. It was fitted properly in the cover but the rubber seal was lipped out at the bottom, like it was sticking it's tongue out. The high pressure must have blown the seal outwards.
I got this bike a year ago and so did not know how long the seals had been in or whether they had been fitted correctly. So I fitted new seals to crank and cam shafts and reassembled. It was only afterwards that I raised the question about oil pressure.
I removed the pressure release domed cap and removed spring, shims and piston. There were 4 shims. I kept reducing the number of shims until I achieved about 55 psi max. This is the upper limit of Norton's recommended 45/55 psi.
On my engine, one shim gives 55psi and zero shims gives 45psi.
This tallies exactly with L.A.B.'s findings. Hope this helps. Cheers.
 
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