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Pressure relief valve

Submitted by john_crocker on Sat, 28/01/2023
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Light Twins

The one fitted to the inside of the timing cover.  Anyone know what pressure it is set to?

I've calaculated it but would like to know what the factory spec was.

I believe that a Dominator PRV was set to 45-55psi, I 'm guessing the same because the bottom end is, more or less, the same.

John

 

 

Submitted by peter_holland1 on Sat, 28/01/2023

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Hi John,

Roadholder September 2015 p6 has a small article on the pr valve.

When I wrote it I didn't put the "correct" relief pressure. I would expect as per Dominator but I noted variable results. A round ball on a good circular seat moving in a housing with enough clearance for particles to get by. That's what you need. And you haven't got any of that in the lightweight pr design.

Good luck with your Norton Lightweight project.

Peter 

Submitted by john_crocker on Sun, 29/01/2023

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A ball is definitely not the way to go.  The ball, being unguided, will tend to "flutter" particularly on closing as the ball finds its own way back to the seat. That is to say will not open and shut with positivity.   The type Norton use, a piston in a cylinder work better because the piston (valve) is guided, a type almost universally used for this purpose.

A ball valve for an anti-wet sumping valve is fine, as Velocette successfully did, is fine, that just opens and closes as the engine runs and stops.  I'm using a ball valve for this on my navigator..

The reason I ask about the setting of the valve is that the pressure seems, to me, rather high.

 

Submitted by peter_holland1 on Sun, 29/01/2023

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Hi John,

You are correct. Pistons and spring are generally used. And pistons jamming in the open position the usual failure mode.

Relief passages should be sized for this eventuality and enough oil gets through to the crank to keep things moving.

Agree with you dommie rv pressures should be good as design uses same seals as Navigator.

Cheers

Peter 

Submitted by john_crocker on Mon, 30/01/2023

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If the ports are sized such that (some) oil pressure is maintained to some degree if the vlave sticks open, then the ports will be so small that the valve will not be able to function as it should.

If the valve sticks open then the engine is in trouble.  This type of valve is usually very reliable.  Neglect is the usual problem, un-filtered oil not changed often enough or bike layed up for an extended period with dirty oil in the sump.

 

 


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