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#880483 05/13/22 10:26 pm
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Referring back to this post:
https://www.britbike.com/forums/ubbthreads.php/topics/861708/3
I made the two piece OPRV:
[Linked Image from live.staticflickr.com]
The bearing ball sits against a rubber backed washer, held in by a spiral ring. A hollow set screw sets the pressure on the ball and allows the oil through to the relief hole.
I had to use RTV on the washer because the diameter of the rubber was the same as the bypass slots around the ball. Making the slots slightly less deep will let the rubber seal against the body. In any case there is no leakage with the ball seated.
Being two piece, the body threads can be sealed in the case without potentially blocking the relief hole. A hex is provided on the body for turning it in.
The cap is just a cover.

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Hi David, as always beautiful work.
I believe this part is intended for motors that have a pressure switch port to allow setting up the pressure relief. If no port available what is the cracking pressure set when built?


Down to ‘69 T120R now a Tr6R tribute bike
‘70 TR6C “happy in the hills”
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‘66 A65L“in ‘95 getting back in the game”+ empty ‘67 Case&Frame *
‘69 A65L
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‘68 A65F nice Tribute bike
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This is just a replacement for the OPRV, works on engines with or without the switch port.
The relief is set by the hollow set screw (lower right), should be 50 PSI for stock but can be adjusted with an hex wrench. I have to test one to see if I got the spring right.

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The earlier engines can be drilled and tapped for an OP gauge. I've done it several times, even on A10's. I like to use 1/16" NPT for doing it because imho space is limited.

Nice looking valve arrangement but I wonder about the oil pressure pushing against the exposed part of the rubber backed washer. It seems to me it might try to move it some and find a leak path there. Does its retaining clip seat in a groove?

Another concern would be the life expectancy of the rubber seat. Why not use a metal seat like most other relief valves out there? Accurate metal to metal can seal quite well.

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DMadigan #880582 05/14/22 10:54 pm
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I've done it several times, even on A10's. I like to use 1/16"NPT

Ditto.
I don't bother with permanent oil pressure gauges but some blokes like 'em.

Even taken the end feed pipe for an a65 from an 1/8 NPT hydraulic fitting drilled and tapped into
the area above the relief valve on early engines. Just careful drilling/tapping and it's fine. Used 6mm
tube. Raced one like it for years.

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You would have to seal the metal seat washer against the valve body. Otherwise you have the same problem as the piston OPRV.
The oil is pushing against the I.D. of the rubber but the ball is pushing against the face. Any radial movement of the rubber from oil pressure will just move where the contact point with the ball occurs.
Yes, a spiral ring retains the rubber backed washer.


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