Adjusting Oil Pressure Relief Valve

[Stephen Hill]

As part of cleaning out the oil sump for the first time, I dismantled the oil pressure relief valve.  And discovered that it was missing a washer that would change the relief pressure. 
Using air pressure, I found the valve was blowing off around 45 psi. 
Factory specs are 54 to 60 psi. 
Adding a missing washer and an extra shim, it now blows off at 56 psi.

I am not impressed with faces of the valve:  they are grooved with machining marks (both the piston and the seat).  Which probably explains a fair amount of leakage prior to the valve blowing off.
 
Question #1:  Anybody cleaned up these faces to try to reduce leakage?
Question #2:  Is setting a blowoff pressure using air a reasonable procedure?   Pressurized oil would be closer to the operating conditions, but hard to accomplish, messy, and should produce the same result, in my opinion.

BTW, I generally followed this procedure, but did not bother dripping any oil into the valve as part of the procedure.
https://www.youtube.com/watch?v=V91Z_KkKraI
I disagree with the guy in the video that the piston/bore clearance is relevant here.

Thoughts??

Stephen Hill

[Antietam Classic Cycle]

http://www.thisoldtractor.com/moto_guzzi_loopframe_oil_pressure_relief_valve.html
The testers shown are for non-filter engines, but can be easily modified so that the filter-engine OPRV will screw in.

I sometimes find it necessary to lap the valve in with valve grinding compound. It's easy to apply if you buy it in the little squeeze tube from Permatex(?).
 
I clean the valve thoroughly (especially after lapping) and squirt oil into it before testing.

[Chuck in Indiana]

I was a mold maker in another lifetime, so have some diamond lapping compound. Used that. Pressure went from low 20s to mid 60s after lapping.

I used this High Tech Tester.. 
2-009 by Charles Stottlemyer, on Flickr

[Stephen Hill]

Thanks Chuck.  I like your high tech tester.  Much more sensible than mine. 
The thread on the valve body is an oddball:  metric, and by memory measures 12.75 OD. Nothing I could find on a "standard" metric table of threads".
To make my "manifold", I step drilled a brass fitting and overdrove a 1/4 pipe tap, which is nominally smaller in diameter, but uses almost the same thread form as the valve body. Managed to get two threads out of the deal before I ran out of tap length.  Held 60 psi no problem........
Ever find yourself in the middle of a dumbass solution you have devised but there is no going back?

Stephen Hill

[Chuck in Indiana]

Thanks Chuck.  I like your high tech tester.  Much more sensible than mine. 
The thread on the valve body is an oddball:  metric, and by memory measures 12.75 OD. Nothing I could find on a "standard" metric table of threads".
To make my "manifold", I step drilled a brass fitting and overdrove a 1/4 pipe tap, which is nominally smaller in diameter, but uses almost the same thread form as the valve body. Managed to get two threads out of the deal before I ran out of tap length.  Held 60 psi no problem........
Ever find yourself in the middle of a dumbass solution you have devised but there is no going back?

Stephen Hill

I first was going to <cough cough> *buy* a tap and make a fancy manifold. Being a er.. frugal..Guzzi Guy, though, "Hey, it's only gotta hold 60 psi.." 5 minutes later with a piece of garden hose, a couple of clamps, and Bob's your Mother's brother. 

[Antietam Classic Cycle]

M14 - 1.5 threads. Nothing "oddball" about that.

[normzone]

I was a mold maker in another lifetime 

Well that explains a lot - is it still only treatable, or did all my donation to research ever lead to a cure ?

[Chuck in Indiana]

Well that explains a lot - is it still only treatable, or did all my donation to research ever lead to a cure ?

It's still not curable, but now I only make fungus. Thanks for caring..

[normzone]

Oh - that helps explain why you're such a fungi ....

[Chuck in Indiana]

<rimshot>

[Stephen Hill]

Antieham writes:  M14 - 1.5 threads. Nothing "oddball" about that.

I measured the OD on the valve body thread for my 1976 LeMans.  Definitely nowhere near 14 mm.  Closer to 12.75.  I couldn't find that in any metric table I looked at.

Stephen Hill

[Chuck in Indiana]

Antieham writes:  M14 - 1.5 threads. Nothing "oddball" about that.

I measured the OD on the valve body thread for my 1976 LeMans.  Definitely nowhere near 14 mm.  Closer to 12.75.  I couldn't find that in any metric table I looked at.

Stephen Hill

Uhh, how did you measure that? Calipers? (pretty close) Micrometers? (right on the money) Scale? (open to interpretation.) 
Charlie's seldom wrong..

[Antietam Classic Cycle]

Uhh, how did you measure that? Calipers? (pretty close) Micrometers? (right on the money) Scale? (open to interpretation.) 
Charlie's seldom wrong..

Here it is with HF calipers. I used an M14-1.5 tap from my brother's Gearwrench set to tap the hole in my tester.

[Stephen Hill]

The bike's back together, so I can't measure it now.  Measuring the wide end of the 1/4 plug tap I used, yup, the valve probably measured 13.75 mm.  I guess I expected it to measure closer to 14, which is why I didn't go chasing a tap. 
Regardless, job's done.  Thanks all for your assistance.

Stephen Hill