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I am sure this has been asked before. What is the normal operating oil pressure on a stock 650 BSA engine? I have tried to search for it but did not find any posts. I have rebuilt my 1971 Thunderbolt engine. All clearances were checked and in spec. Crankshaft rod journals was reground .010 and new bearings. Left side crank bearing replaced, and clearance was .0015 on right side bushing. I replaced the pressure release valve and new ball bearing and spring under oil pump. I inspected the oil pump and it looked ok. The light was coming on at idle after engine has been ran and warmed up. I installed a manual gauge and when engine is started it has 45 psi oil pressure. After riding it for 10 miles it runs at 38 psi at 3000 rpm. This is around 50 mph. At 2000 rpm it still has 35 psi. When at idle is around 6-8 psi. I have checked and replaced the switch for the light. I am using Castrol 20w50 oil. I did not replace the oil pump as the gears and body looked ok. I have spent a lot of time and money on this motorcycle and want it to be right. Any information is appreciated.

You are probably loosing pressure via the relief valve.
There is is thread somewhere which goes into a convoluted
method of correcting it using an external oprv. In short the
valve leaks pressure to it's drain port via the threads. If
you seal the lower part of the threads with a good sealant, after
drying and cleaning the aperture, then replace the valve, it should
be better. 6-10psi on tickover is no problem, it should ride at
40-50psi when warm. If the light comes on at tickover, get a switch
with a lower setpoint, 6psi is plenty. Remove the gauge, they are
a worry gauge and serve no practical purpose once you've finished
testing/setting up.

If you slightly rev the bike and the light goes out at 1500 rpm I wouldn't worry about it. My 70 did that for years. You have good oil pressure at 2000 and 3000.

Turn the idle up a little till you sort things out
+1 for leakage via the OPRV

I believe the standard oil light on an OIF A65 is set to <6psi so i wouldn't worry about the oil pressure at idle.

SRM engineering in the UK make OPRV that are calibrated on an oil pump rig to ensure they don't release the pressure too early, and are supposed to seal better than standard ones. But if youd rather not spend the money a sealant should do the job. I have had one fitted to my A65 however ive not had it running yet so i can speak to the quality of it.

https://shop.srmclassicbikes.com/product/stainless-steel-pressure-release-valve-bsatriumph-twins

I searched "Britbike forum A65 oil pressure", this is what I got.
https://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=496286

https://britbike.com/forums/ubbthreads.php?ubb=showflat&Number=283634&page=1

To Search effectively use Google, the forum search facility is very difficult to use,

The 71 should have the piston type relief. The issues of the oil cavity drain are much improved over the early engines. Still not a bad idea to put sealant on the lower threads to seal better between oil supply and oil drain.

Make sure the OPRV sealing washer is correct. A lot of gasket kits use a thick washer, you need one about 1/32” thick. If the cavity has a bit of a chamfer on the outer edge, toss the gasket and use a thin section O-ring as a seal.

This is more arcane. The cavity for the oil pressure switch is drilled at an angle to intersect the main oil passage. IME, on many late cases, the angle of the drilling is a bit off and the cavity for the oil pressure switch barely breaks through the oil galley. Very little oil gets to the switch. In effect, you have an orifice showing low oil pressure. It is made worse by the oil pressure switch cavity not really having any flow through it. On bare cases you can open it up, on a built engine, you are screwed.

You might also consider using a different oil. Especially in warm weather. Since you have gauge fitted try #50 and see how it behaves. I think you will be happy.. PRT

I remove these becasue they are a cause of low pressure issues as the stainless piston in the stainless body wears and lets oil past - if your lucky it'll just do that, in other cases they stick... Open.

LF Harris make some OPRV's (I have one fitted to my Thunderbolt) and its quite a good item. The one I fitted is for the Trident/Rocket 3 and A70 which has a 70PSI blow off, though some of the advertising blerb for the OIF stated a 70PSI unit - though seldom seen them fitted.

I also have some NOS 50PSI unit. with the end of the oil pump quill on a drill, you can spin the pump up beyond 70psi. and comparing the two OPRV units, the 70PSI unit definately blows off pressure at much higher pump speed than the 50psi unit.

Your oil pressure doesn't sound too bad to me and in addition to checking the OPRV threads, it may be worthwhile following the advice given on the E&V engineering page about A50/A65 oil pump installation see This Link

Basically, the idea is you remove the inner timing cover and timing pinion but keep the oil pump installed. The pump is then turned using a rubber pipe attached to the tacho drive using a cordless drill. The pump will turn and draw oil which is then passed past the OPRV to the main journal and big ends.

As pressure builds you should hear the OPRV blow off and then check for any leaks between the pump top and bottom plates. Often oil is seen squirting out from the top & bottom plates and also from behind the gasket. Any leaks mean you are losing oil pressure, so worthwhile fixing.

I bought an OPRV from SRM. The stainless piston was scored after very few miles.

A design no no, worse than the Concentric Amals with the body and slide made from the same Zinc alloy materials. Stainless is easily galled even against another material but stainless to stainless is the worst. A simple use of a bronze plunger in a stainless body would be a much better solution.

Or cast iron, or free-machining brass.

Hey, speaking of the arcane and fear of OPRV issues, I closely examined an OIF relief valve, the first and only one I have ever opened. It was from a basket case complete with frass, cat hair etc. Disassembly was a little _itch but with the right sockets I got it apart and found a precision device on the inside. Looked new with precise machining. I decided to do some calculation and assumed 80 psi as the waste/bleed point and came up with the required spring rate. Without a test rig and too lazy to create one, I never tested to see what the actual waste/bleed psi was for my catbox basket case OPRV.

Having written the above and as lazy as ever, just wanted to ask if anyone has identified the actual spring rate? Wouldn't a shim behind the spring add preload and result in increased oil pressure? Naturally, if there is a leak past the threads it would be good to seal and also use an appropriate thickness gasket.

Too hot and lazy to drive 400 miles to Mid Ohio and back 400. I'm sure there is stuff there I need to make my 71 Lightning look almost as nice as the OP's.

Generally, the valve does not cause low hot pressure. The loss of oil downstream of the pump exceeds the capacity of the pump.

This is how I checked it with my wife help:

https://www.youtube.com/shorts/fiIm01Z0tfs

But this is cold oil on a cold engine after my past experiences will be using 10W60 oil in this engine to have a decent pressure on a hot engine tick over.

The best way to stop the oil pressure warning light coming on with a hot engine at tickover is to fit an oil cooler. Even a small one works well. Put it on the return side of the system as that is when the oil is the hottest and so cools the most. I did this on my OIF bike and haven’t seen the oil light come on since, even with a very low tickover speed and a very hot engine. Previously it was always coming on all the time once hot.

You were lucky, Ive found oil coolers only reduce the oil in the tank by a couple of degrees at most. Not enough to stop the oil light coming on at tick over. Removing the "stainless" oprv for a ball type or original BSA OPRV has resolved the issue (noting that the stainless item was sticking).

First thing I would do now, if I was to see this issue would be to change the oil if using a multi-grade. If the oil cannot maintain its viscosity (and thus pressure) when hot then the viscosity modifiers have done their job and connot do anymore, your now running a SAE 20.

You could try a higher grade oil, but I prefer to use either a monograde or synthetic.

Hi All,
Allan G,
20 plus years ago I fitted an SRM stainless PRV to my A10 Super Rocket,
A few years ago after reading of your experiences I took mine apart to inspect it, It was in perfect condition, I repeated the exercise at the last major service in 2021 and the piston and bore are still in perfect condition
I will accept that if there was dirt or metal particles in the oil it would cause trouble
I have put 30k miles on the bike using SAE 40 Castrol

John

Your probably lucky, and possibly a mono grade oil is most suitable. I have stripped apart (or seen others strip them apart) 3 of these units and most not from my ownership, and this was after hearing stories about issues with them.

If your happy with how it functions and have checked the condition of the piston and all is well then that’s a good thing. I bought mine about 15 years ago. Mileage covered was much less than 30k. Maybe manufacturing tolerances have changed in those 5 years?

All the bikes I have/work on are fitted with aftermarket filters, and never seen any issues since fitting the lyford classics ball type oprv (incidentally my friend is using one on his oil in frame and it stopped the light coming on at tick over instantly when hot) . I now use the piston OPRVs from either NOS BSA or I have a 70psi unit on the OIF 823cc bike.

For what its worth, I've had an SRM OPRV fitted to my A65 for several years following a complete rebuild and although my subsequent mileage is probably less than 5k, following inspection last year I couldn't see any evidence of galling or wear.

I accept that a stainless steel piston in a stainless bore may not be the best solution, but my limited mileage hasn't shown any issues so far.

I once had an OEM BSA piston type OPRV (which I believe are the same as Triumph from the the same era) and the quality was outstanding, I believe the piston was made from some kind of hardened steel which made it immune from wear or galling with the body. If you can find an OEM BSA OPRV I would use that in preference to the SRM type.

The other issue with the A65 OPRV as already mentioned are the minimal threads between the pressure side and blow off side. Ideally when fitting the OPRV, the inner threads need to be sealed with loctite or similar to prevent pressure leakage.

One other thought is that the OPRV only really comes into use when the engine is cold and the oil is thick. The OPRV is usually designed to blow off excess pressure somewhere between 50 to 60 psi. The intention is to avoid over pressuring the oil system which might cause the lip on the crank oil seal to invert and loose pressure. In normal running with a warmed engine the OPRV hardly comes in to play unless the engine is really revved hard and pressure exceeds 50-60 psi.

If the ambient temp in your area is above 30c then it might be worth using a 20W60 oil which will help the oil pressure.

You'll only invert the seal if the motor has had an end feed conversion.
What will/does happen on a standard motor is that the pump is subjected
to high load and it and it's drive will wear excessively. The monkey metal
pumps will distort as well.
I'm not a lover of using heavy oils in these old crates as oil flow is as
important as viscosity. I've taken a few apart that have been run on various
'glue' type heavy oil and they have all shown evidence of poor lubrication
on various parts of the engine. A 20w-50 is fine across 99% of uses, if
pressure is poor then something else is not correct, filling the thing up with
grease is not a kosher way to go. I have raced over here on 42 deg days
and only ran a 30 weight oil with no cooler in circuit as it would cool the
oil too much, it should see 70-80 degs to work properly.

Good point, I only mentioned using 20W60 as I once tried using it on my Norton Commando which had worn big ends, it did make a few extra PSI but the real issue was that the big ends were worn out.

Now that the Norton has had its bottom end rebuilt I'm easily getting 35psi at 2k rpm and 45psi at 3k rpm, and 18psi at idle, all on 20w50 Motul classic oil.

It was really worthwhile fitting an oil gauge to the Norton which initially showed poor pressure and a worn engine, I wish I could fit an oil pressure gauge to my 1968 A65 but there's no easy way, so I have to assume all is well since the engine has only covered a few thousand miles after a complete rebuild.

Talking about 10w60 oil, I use fully synthetic Motul or Liquy Moly oil. These are very far from glue and have great flow as well as viscosity.

I don't really care if you use NASAR space ship oil........

If your a65 suffers with low oil pressure running on 20w50 sg oil
then something other than the oil is not correct.
The pump could be worn, the oprv may need attention, the t/s main may
be worn etc, etc.
Of course, you can get around the fact sometimes by running non specified
lubricants but isn't that just masking the problem?