OPR valve shims and spring specs

Jonez69

Jonez69

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My OPRV had one shim when I tore it apart for cleaning and inspection. Andover-Norton parts book says two are required. Workshop manual says it is set and shimmed accordingly at the factory.
I found no spec for spring length either. I assume the only true measure is to check pressure with a gauge once I am at that point. Everything looks good and the piston moves smoothly.
I can't see any reason not to run it as I found it and check pressure later. I'm just left wondering about the AN parts book stating 2 are required. My paper parts manual calls for five!
 
According to Mick Hemmings in his video, you assemble the PRV and shake it. If you hear the piston moving, add shims until it doesn’t move when you shake it.

Seems sound advice to me. If the piston is able to move ot means it will not be seated even at zero pressure, which is kinda scary. Whereas if it’s seated by the spring, this will keep it closed until a certain pressure is reached.

By that logic, I’d suggest that one too many shims is always better than one too few.
 
I thought Mick Hemmings said to add shims until the rattle stops and then remove one shim so it start rattling again ?
 
kommando said:
I thought Mick Hemmings said to add shims until the rattle stops and then remove one shim so it start rattling again ?
Click to expand...
Yes, my search here before posting this thread found comments mentioning Mick Hemmings and his rattle method. I was just hoping for some clarification as to how I should proceed.
 
Jonez69 said:
Yes, my search here before posting this thread found comments mentioning Mick Hemmings and his rattle method. I was just hoping for some clarification as to how I should proceed.
Click to expand...
The vast majority of the time, the valve is doing nothing. It releases pressure if it gets too high. Put in two shims. If it worries you, add an oil pressure gauge temporarily and see what the pressure is when the engine is cold and at high RPM. Then decide if you're happy with it.

Most of the time, the pressure will be well below where the valve releases pressure.

More important to be sure the oil pump and seals are in good shape so you have enough pressure!
 
marshg246 said:
More important to be sure the oil pump and seals are in good shape so you have enough pressure!
Click to expand...
Yes, I did go through the pump and followed the procedure outlined in the workshop manual. For the price of the shims, I will buy a few and check it with a gauge once running.
It won't take much work to check out my 73' 850 since i will have extra shims. Here's a picture of my progress. Thanks everyone!
OPR valve shims and spring specs
 
5 shims would be around 200 psi cold. Might not work out so well. I tried 2 in my not Commando and had 80 psi cold. Pulled one shim out and it is around 60 psi cold, which to me makes more sense. One man's sense is another man's dumbf_ckery. Just thought I'd mention that.
 
Schwany said:
5 shims would be around 200 psi cold. Might not work out so well. I tried 2 in my not Commando and had 80 psi cold. Pulled one shim out and it is around 60 psi cold, which to me makes more sense. One man's sense is another man's dumbf_ckery. Just thought I'd mention that.
Click to expand...
Yes, I just found it interesting that Andover Norton website parts listing says two REQUIRED. My paper parts manual says Quantity 5. The workshop manual says the OPRV is set at the factory and requires no attention . The bike is 52 years old and I open up the valve and there is one shim. Who knows if a previous mechanic has had the OPRV part or not.
As I am a relative Norton newbie, I simply wanted to be on the right page. I 'm sure at first start up that everything will be fine. As @marshg246 points out, the valve only comes into play when the pressure rises to a certain point as controlled by the spring pressure and number of shims. @L.A.B. is spot on with advice to hook up a gauge and be certain of your bike's oil pressure.
 
Jonez69 said:
The workshop manual says the OPRV is set at the factory and requires no attention . The bike is 52 years old and I open up the valve and there is one shim.
Click to expand...

However, after 52 years it could possibly do with checking again.

Jonez69 said:
My paper parts manual says Quantity 5.
Click to expand...

As I've already stated "5" is the the quantity of shims in the original NM.15404 shim pack.

The OPRV should normally take 0 to 2 shims.
 
Jonez69 said:
The workshop manual says the OPRV is set at the factory and requires no attention .
Click to expand...
Don't take that literally! I'm sure no one was individually testing and changing shims as they built bikes! In fact, I'm pretty sure the valves came assembled and were screwed into the cover in the Norton factory. You can bet that whoever made the valves had a specification and tolerances and they tested what met that and moved on. It's also possible that Triumph got their valves from the same place and they don't have shims.

This is simply not that critical! Your bike was working with one. You can be sure that two will hurt nothing and if you put in 0, the world won't end.
 
Jonez69 said:
Yes, I just found it interesting that Andover Norton website parts listing says two REQUIRED. My paper parts manual says Quantity 5. The workshop manual says the OPRV is set at the factory and requires no attention . The bike is 52 years old and I open up the valve and there is one shim. Who knows if a previous mechanic has had the OPRV part or not.
As I am a relative Norton newbie, I simply wanted to be on the right page. I 'm sure at first start up that everything will be fine. As @marshg246 points out, the valve only comes into play when the pressure rises to a certain point as controlled by the spring pressure and number of shims. @L.A.B. is spot on with advice to hook up a gauge and be certain of your bike's oil pressure.
Click to expand...
You won't be a newbie after you get done with putting it back together. Besides it's just nuts and bolts and a little bit of tolerance measuring. Easy Peasy. You can move right to expert in no time. :)
 
marshg246 said:
Don't take that literally! I'm sure no one was individually testing and changing shims as they built bikes! In fact, I'm pretty sure the valves came assembled and were screwed into the cover in the Norton factory. You can bet that whoever made the valves had a specification and tolerances and they tested what met that and moved on. It's also possible that Triumph got their valves from the same place and they don't have shims.

This is simply not that critical! Your bike was working with one. You can be sure that two will hurt nothing and if you put in 0, the world won't end.
Click to expand...
I fitted a new OPRV assembly and a new timing cover (mk 3 design), and ended up shortening the free length of the spring by 2.1 mm to lower the cold oil pressure down to 65 PSI (without shims). It is worth the effort of checking the cold oil pressure on the first start up and not taking the risk of blowing the crankshaft oil seal inside out or dislodging it,s circlip.
 
justin scroope said:
I fitted a new OPRV assembly and a new timing cover (mk 3 design), and ended up shortening the free length of the spring by 2.1 mm to lower the cold oil pressure down to 65 PSI (without shims). It is worth the effort of checking the cold oil pressure on the first start up and not taking the risk of blowing the crankshaft oil seal inside out or dislodging it,s circlip.
Click to expand...
Where did you get the OPRV?
What pressure did you see with the shim(s) and uncut spring?
 

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