Oil pressure relief valve, 1972 Commando

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Mark Savage

Mark Savage

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I stripped my OPRV down for a clean and it's not how I expected it to be, ie, cap, washer, shims, spring, plunger and body. It was cap, spring, ball and body. Also it was heavily sprung. This doesn't seem right to me and wondered if this was a different version or just totally wrong. It's been like it for years. I'm wondering what the consequences are of it not being able to relieve properly if that's the case. TIA.
 
That's the way they are. They're not a regulating valve, just an over pressure relief for cold oil. Once the oil is warm it'll never get close to the relief pressure.
 
ball????? TOTALLY WRONG for 72 and mostly all NHT except in the 57-59 era. (can't talk about it here cause it's not commando)
Wonder since you are in the UK have access to other brands that are close. Could it be a aftermarket or BSA A-65.
My BSA A-10 OPRV is really close to a NHT. It is even a piston type.
Just for piece of mind, I'd suggest to get a real norton one.
But as JimNH said... once the oil is hot it does nothing. And in general as long as it is free to operate I don't worry much now that I do know exactly how they contribute to the oiling system.
 
Dommie Nator said:
It's been like it for years. I'm wondering what the consequences are of it not being able to relieve properly if that's the case.
Click to expand...


I think what would be of more concern is how much leakage (if any) there is through the valve due to the fit, and whether a ball instead of the normal plunger shuts off the flow when 'seated'?
Can you blow through the assembled valve when it's closed?
Maybe fit a pressure test gauge to see if it actually works?
Or just fit a new OPRV?


dynodave said:
ball????? TOTALLY WRONG for 72 and mostly all NHT except in the 57-59 era. (can't talk about it here cause it's not commando)
Click to expand...

There's nothing to stop you talking about it IF the information has some relevance to the Commando (which I'm not sure '57-'59 era model info would be in this instance.....but??? :? ).
 
I missed the ball v plunger part, sorry.

I am a firm believer in gauges. My bike relieves at a surprisingly high value on the test gauge which I can't recall right now. I have a 80lb gauge that pegs hard when cold installed now. Bike runs 50psi plus back road cruising and somewhat less after a highway 80 mph trip.
 
Well thanks for the response so far. I have put a picture up on the Access Norton Facebook page if it helps (link to page at top of this page, hit community). The spring put loads of pressure on the ball even before it's tightened I am also a little baffled as to why oil kept coming from the aperture once I removed the valve, I reckon I could have drained the tank if I left it open. I have now put one in from my Dommie.
 
Dommie Nator said:
I am also a little baffled as to why oil kept coming from the aperture once I removed the valve, I reckon I could have drained the tank if I left it open.
Click to expand...


Oil from the Commando OPRV is sent back to the inlet side of the feed pump through a drilling, it isn't just dumped into the engine where it will be scavenged (unless it's an 850 Mk3 or has a Mk3 timing cover) so if the OPRV is removed, the oil tank will drain.
 
I needn't worry? I took the OPRV of my Dommie to do a swap and hardly a drop came out.
 
Dommie Nator said:
I needn't worry? I took the OPRV of my Dommie to do a swap and hardly a drop came out.
Click to expand...

Dominators don't have the 'return' gallery between the OPRV and the feed pump inlet so the Dommie tank won't drain.
 
Thanks for the info. You're a star. I'm just a little baffled as to why someone would put a wrong valve in to begin with and of course what else is lurking within. :shock:
 
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