oil pressure relief valve

No one really seems to know about these things.
The "correct" way to judge good from bad is to hold it up to your ear and shake it. "If it rattles, it is OK..."
Not that I have much faith in this method, but the next question is...How much rattle? I checked mine and found it was clean and the piston moved freely. There were NO shims. It rattled a lot. I do not think "more is better" in this instance. So I cut a shim in the lathe so it would just barely rattle...took 3 tries to get it. Good? Bad? Does anybody really know?

The most accurate method of checking operation of the relief valve is with an oil pressure test gauge in my opinion.

In the parts book the shim is shown between the spring and the cap nut. From reading various posts in the past that seems to be the norm. However when I took my pressure relief valve apart I discovered that there was a shim actually between the spring and the piston which could be easily overlooked. To get the shim out I rapped the piston on the table top a couple of times until the shim fell out. Maybe you have a shim in your piston as well.

Since you have a lathe you can make an oil pressure gauge adapter that would temporarily replace one of the oil line banjo bolts on the head. I made one out of 9/16 brass hex stock that I had lying around. It didn't take very long to make. The gauge simply screws into the fabricated banjo bolt. I ended up adding a shim to my oil pressure relief valve which made the oil pressure gauge read 50 psi when the pressure relief valve opened. This is with the engine cold. Any higher than 50 psi on your pressure relief valve in my opinion would just add more stress to the oil seals within the timing cover. Here is a picture of my oil pressure gauge adapter. Maybe it will give you some ideas:




Peter Joe

Matt Spencer said that the cap and pressure indicator button off a 50s Triumph fits the Commando base. Is this true ?

the adaptor is a good idea, I can make one.

One time I had the valve seize in the closed position and it INVERTED the crankshaft seal and caused a lot of grief with my engine breather .....actually, my breather got saturated with oil and that is how I found out about the stuck valve.

I tried to build a test unit for the OPRV but I ran into several problems. First, it was a small tank that I could fill with #30 oil. Then by using a tank of CO2 I could use the regulator to pressurize the cylinder and find at what PSI the valve opened up. HOWEVER...there are only about three threads that hold the OPRV in the motor and those have plenty of clearance. Oil would flow past the threads quite easily and back into the motor. I could never get a good reading. Tried teflon tape which helped quite a bit but the piston would also leak a lot, even when cold. Imagine when hot. So I could not come to any reliable conclusion other than I would like a much better designed system. So...I am back to the highly unreliable system of " how much rattle is good enough?" I cut my shim so it would allow a very small rattle. Do not know if that is correct.

I bought an OPG from RGM a few years ago and got some pretty strange readings. tried to speak to mick Hemmings about them , I had spoken to him about other things and had good results, however on this occasion he was quite adamant that they told you bugger all. So with a flea in my ear I removed it , forgot about it and just rode the bike.
When I built first engine shimmed it till the OPRV just rattled and rode the bike fine , but I still don't really know why mick thinks that OPG are a bad idea. By the way neither engine so far has ,seized , blown up or makes excessive noise.

Since you have a lathe you can make an oil pressure gauge adapter that would temporarily replace one of the oil line banjo bolts on the head. I made one out of 9/16 brass hex stock that I had lying around. It didn't take very long to make. The gauge simply screws into the fabricated banjo bolt. I ended up adding a shim to my oil pressure relief valve which made the oil pressure gauge read 50 psi when the pressure relief valve opened. This is with the engine cold. Any higher than 50 psi on your pressure relief valve in my opinion would just add more stress to the oil seals within the timing cover. Here is a picture of my oil pressure gauge adapter. Maybe it will give you some ideas.
Peter Joe

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When the oil is cold it would give you a higher reading on the oil pressuse gauge, so wouldn't it give a more accurate reading when the oil is up to the right temp, when the oil warms up the gauge will drop to a lower reading on the gauge, so wouldn't it be better to have a reading of 45 to 50 psi when the oil is at the right operating temp.

Ashley

ashman said:

When the oil is cold it would give you a higher reading on the oil pressure gauge,

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If the OPRV is set to blow at 45-50 psi then it will open at that figure, hot or cold.

ashman said:

so wouldn't it give a more accurate reading when the oil is up to the right temp, when the oil warms up the gauge will drop to a lower reading on the gauge, so wouldn't it be better to have a reading of 45 to 50 psi when the oil is at the right operating temp.

Click to expand...

As the oil heats up and thins out, due to the limited pump capacity, the oil pressure can eventually drop below the point at which the OPRV will operate, so attempting to set the OPRV 'hot' is likely to be a waste of time. Excess oil pressure in a hot Commando engine has never been a problem as far as I'm aware?

Here's a previous discussion on this subject: oprv-impact-hot-oil-t19321.html

From Mick Hemmings DVD, remove shims one at a time just until rattle. Not scientific but easy.

" Fit OPRV and Cross Fingers"...I think it is all we can do short of a guage. Maybe my machined up shim is good.