Triumph Bonneville T140 Oil Pressure Relief Valve Service OPRV 

Thank you.

The OPRV was part of my process in finding out why I had low oil pressure at tick over and no feed return to the tank. I will definitely take a look at replacing the oil seal, as you say it's easy enough to access and cheap enough to do.

My valve had a severely stuck piston. I could not budge it. The motor wet-sumps in less than a month. Had over a quart in the sump. I have a new valve on order.

@@steveburke3923 I don't think a stuck OPR valve can cause wet-sumping, because the ball and spring valves in the pump should stop oil from going any further when the engine is not running. If oil is getting past those, that is where your problem is likely to be.

It keeps the oil pressure within design tolerances. Off the top of my head on a hot engine at mid range it should be around 70 psi and at idle 20 psi, but don’t quote me on those numbers. Too high a pressure can blow seals and gaskets causing a drop in pressure and the inevitable premature wear on things like your big end bearings, which isn’t good… 😂

As for how it actually works, the gallery supplying pressurised oil to the crankshaft has a drilling spurred off it, leading to a chamber housing a spring-loaded piston. The spring is precisely rated so that when the oil pressure acting against the piston reaches the pre-set value, it pushes the piston far enough to open the bypass ports and allow the excess oil to bypass the crankshaft and drain straight into the crankcase. It will then balance oil pressure against spring pressure, maintaining it at the maximum specified and preventing the seals from damage by excessive pressure, as already described above. The warning light is a separate thing, working at the other end of the pressure range: also screwed into the oil gallery is a switch with contacts which are normally closed. When the oil pressure reaches around 5 psi, it opens the contacts, breaking the circuit and extinguishing the light, so it only tells you that there is some oil circulating, not that the pressure is good.

@@rickconstant6106 thank you. That was a great explanation of how it works. Now I know. : )

There can be many reasons for oil pressure problems low or high. Damaged pump, worn main bearings, blocked filters, poorly operating valves. Turns out mine was perished timing case oil seals.

@@bodganeering Years ago, a friend of mine had a 1972 Tiger & the oil seal failed on the timing cover. I believed this caused oil to leak out from ignition points area/cavity. I helped him put a new crankshaft seal on timing cover. I have a 1973 Tiger that I purchased in 1977. I probably had less than a year when I had an Oil pressure problem. I took it to a local independent shop & they fix it & I was told it was due to the a check valve in oil pump. The bike now has 63,000 miles & runs good.

Pot luck with Triumphs. You either get a solid machine that will give thousands of faultless miles or one that will spew its oil out at the worst moment, the later normally been built on a Friday afternoon.