Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A65: another oil pressure thread....

hey guys- i know this topic has been talked to death, but the search function on this site makes it very difficult to turn up old info. if anyone can post links to old threads, please do. otherwise, forgive me for the redundancy.

as some of you know, i recently rebuilt the engine in my 1971 A65T. some of you might also remember that i bought it from a member here, who came posting about low oil-pressure and a knocking sound once warmed up. upon disassembly, it appeared that the classic timing side crank bush was the culprit. all bushings and bearings were replaced, and all clearances are perfect. the oil pump is alloy, but looked very good on the inside. the PRV is the domed type.

the problem: once the bike gets nice and warm, the oil pressure light starts coming on well above idle. i could be paranoid, but i feel like the reciprocating sounds in th engine also got a little louder under these conditions. i'm worried about a lack of oiling (obviously), and want to make sure the pump and PRV are working properly.

first off, i remember reading references on here to problems with the PRV and gaskets.. can someone point me in the right direction? i'd hate to kill an engine i just put some much work into rebuilding, so i'd like to know everything's working right.

I wouldn't rely on a warning light, in this situation especially you need a gauge so as to see what it does above the 7psi or so the light switches at. What grade of oil are you using? Sometimes after sitting a long time the relief valve spring can collaps, becoming short and cause low pressure, they have a set length, and can be stretched easily back to size forcing a little screwdriver shaft between the coils, you don't want too much pressure though 80psi cold they seem to handle but over 100psi and its trying to push the pump apart.

I have the same sort of thing going on, except mine is not newly rebuilt and has a gauge and filter.
Everything is fine: 80 psi at first, dropping to 60psi after a few miles. But, after about 10 miles at highway speed pressure starts going down. If I keep the revs up, it still manages 30 to 40psi, but it scares me.
Valvoline VR 20/50 oil. Iron pump, piston-type OPRV.
I'll clean the sludge trap this Winter.

If the oil is getting hot it may be worth putting an oil cooler on it which would keep the oil cooler and the pressure up better.
I'm very much an advocate for roller conversions and end feed, for such nice bikes. I notice Edward and Bella sitting on a nice A65. Newmoon isn't released out here yet but does anyone know if they use the BSA in the movie?

i have a pressure gauge.. i'll install it directly at the idiot switch junction just to be sure. i haven't installed an external filter, but will soon (i know, kinda silly not to do it during break-in if i'm going to). i run 20W/50 oil. 30 or 40 PSI sounds safe to me... 7 PSI (light still on) at 3000 RPM, not so much.

i was planning to test running pressures... i juts remember reading somewhere on here about PR valves not working properly with the wrong washer or something like that. ring a bell anyone?

Hi,



Ime, BSA publications were less-forthcoming about oil pressure than Triumph ones. Until someone expert comes along, from my experience of Triumph twin engines, 80psi cold, 60psi hot above 3,000rpm, 25psi hot idle; I'd allow the latter to be 50psi and 20psi respectively but not much less. Based on that, imho 30psi normal running pressure is too low.


You should find the thread is 1/8"NPS but keep an eye out for 1/8"NPT. When Triumph and BSA started fitting o.p. switches at the beginning of the '69 season, the taper-thread switch is what was used for the first few months; these bikes have been around for a long time and bits got swapped about.

Edit: Hmmm, I just read in the OPRV thread on the Triumph Board that the BSA OPRV is set to only 50psi.

Hth.

Regards,

Don't know if that 50psi is an exact setting or what one could expect under good conditions, it may be that hot at some rpm the valve isn't bypassing anymore. With an end feed conversion it usually is higher, having only two bearings to pressure feed, but is always temperature sensitive, and pressures 80C 60H and 30-40H at idle easy to get.

1. The OPRV should be sealed to the case with a very thin washer. Some people supply a very thick fiber washer for the OPRV. If you have a thick washer, toss it. I chamfer the cases and use a thin o-ring in the groove on the OPRV for a seal.

2. Many late engine have crap cavities for the switch. It is angle drilled into the main oil galley. Many (but not all) cases have very little "break through" into the oil galley. In effect, you are measuring oil pressure through an orifice. When you put oil through an orifice, you deal with pressure drop . I have measured as little as .015" break through. I don't know of an easy way to fix this issue. Even a gauge is going to read very low oil pressure with this type of cavity.

3. Make sure you have the right pressure switch. BSA used a lower setting switch than Triumph. The commonly available switch is Triumph.

4. If the engine actually has low oil pressure, pull the sump and see if you have shinies....

5. Did you install an SRM relief? IME, it is better made and works better than the stock BSA relief.

the OPRV is sealed with a thin washer.. there was a thicker one in the kit, but this information is what i thought i had remembered, and so i left the old one in there. i'll pull it off and inspect again.

i can't say for sure if i have the right switch, but it appears like the OEM unit in my '71 parts diagram. i should probably spring for the SRM product.

i pulled the sump plate when i did my first break-in oil change, and there were no unusual shinies... a little metallic color to the oil, which i'd expect with new bushings and rings.

Hi Paul,

I went through the things you are going through right now. I have the SRM OPR and a Lockhart Oil cooler with thermostat plus a Norton spin on Filter on the return line. Since then I ended up having the engine rebuilt and when the motor got hot the light would still come on.

I replaced the pressure warning switch with one from NAPA but I had to mount it on an extension as it interfered with the case. My switch goes on at 5 psi. I am running Spectro Golden 4 oil 20W50 with some Lucas Stabilizer (which thickens things up a bit). This keeps the light out.

When I rebuild the Firebird or the Star I will do the roller bearing conversion as the timing side bush can't be anything less than perfect which seems to be too much trouble in this day and age.

Paul:
FWIW loads of Brit cars used the same LOOKING oil switch, most but not all of them were stamped with psi in variuos places.They seem to vary from 7-12 psi, probably with everything in between.

gauge is the way to go if you can fit one.

can anyone tell me the correct length of the spring in the late (domed) OPRV? i swapped mine out for a spare (with no positive change) while inspecting mine, but can't find specs on it anywhere. my spring measures at 1.25" in length.

I do have a small oil cooler in circuit.
I have read in other posts that the cavity for the switch was not the best. I wonder how accurate my gauge is, being mounted to that orifice.

David,
"I wonder how accurate the guage is"? That's a good question. Generally the gauges made tday...even the cheap one's are fairly accurate...mayby not to a a couple psi, but within a range they are OK. What makes a guage inaccurate or more correctly misleading is if there is a lot of oil flow going to bypass it will create a pressure drop in the system especially in the area where the gauge/bypass is located. You could be getting misleading readings. I tested my 66 A65, which has no provision for measuring oil pressure. I made a test rig where I totally closed off the bypass and and measured my oil pressure. Believe it or not I had good oil pressure...about 18psi at hot idle and around 55psi at 3000 rpms, and it pegged my 0-60psi guage at any rpms beyond 3000. Of course when I took out my test setup and replaced it with the later OPRV, my system could have lower pressure at the bearings because of an improperly functioning OPVR or becuase of internal leaks or because of orifices so small that the pressure at the bearings cannot be maintained at a high level. A pressure relief valve is installed on most all engines for a couple of reasons (1) To prevent over pressuring the bearings. I have read that 60-80 psi is about the maximum allowable pressure for the early soft (copper/lead alloy) bearings. (2) the second reason is to limit pressure so that you are not wasting HP or wearing out your pump. Gear pumps if deadheaded can make very, very high pressures. Since most modern engines use gear pumps, pressure relief valves are a necessary part of the system and BSA's are supposed to relieve at around 50 psi. I am getting by with my original el-cheapo alloy pump. I would like to have a heavy duty billet type pump that is well torqued together and has the proper internal gear clearances and enough volume to always keep the BSA at optimal oil pressure. Plain bearing motors have been around for a hundred years and there are pumps and relief systems that are reliable in these motors for several hundred thousand. BSA recognizing this changed pumps and OPRV late in the game. If you are woried about your pressure, you can make a test rig to see what kind of pressure your pump makes out of the original OPRV with the little ball and spring. Other than that, upgrade to abetter pump , a better OPRV, and cross your fingers.

Mr Mike

mike,
if you make a test rig mounted at the OPRV orifice, won't this only tell you what pressure you have without any PRV at all? seems helpful to know your pump is working well, but still leaves the operation of the OPRV to be tested at the sending switch. still, knowing the pump is making adequate pressure is a good starting point.

Paul,
You hit the nail on the head. I know my pump makes adequate pressure...there's some comfort in that. I can't be absolutely sure that once I have the OPRV back in that I am making good pressure at the bushing and rods. But after doing the test, I quit worrying about it. Every year or so I perform the test again and so far it has shown good oil pressure. My rebuild only has about 8000 miles (I ride several bikes) on it but it sounds and runs the same as it did back when I rebuilt it.

I considered making an external relief directly to the tank with a guage plumbed into the cavity and the bypass loop down in the cavity closed. But I never bothered. You know about that old thing called a "Round Tuit".

Mr Mike

Its no use kidding yourself,guys. The gauge readings you are getting are as accurate as that gauge can be ,in any installation.
The gauge is on the pressure side of the OPRV.On the "dump" side of the OPRV the pressure is less,approaching zero.The pressure is high (or should be),anywhere on the pressure side of the OPRV.

As for the orifice size at the gauge fitting,it wouldn't matter if it was only 0.003" diameter .Once you've filled the cavity in the pipe and gauge (and this only takes a second or so),the reading is true.If you have a large enough oil leak in the pipe or gauge-head,then it will not become filled and you could get a reduced reading.

The whole plain bearing system only consumes about as much oil as you could pump with similar pressure through an orifice 1/32" diameter,exhausting to atmospheric pressure.
Check the OPRV spring and all clearances on the OPRV.

Hope this helps,I just don't want you barking up the wrong tree.
Pete.

Hey Pete,
No one is kidding themseves. There must have been 50 posts over the years that go like this: "I recently rebuilt my A65 bottom end and after a long ride I notice my oil pressure lite starts to flicker at idle. So I stuck a guage in there and I had 50 psi at startup but after about 10 miles the pressure dropped to 5 psi...should I keep riding it?" The system does not seem very robust based on all the chatter over the years and I guess every one wonders why. That is why I tested mine. If I had know the history of these bikes I would have drilled and tapped a port for a guage when I tore it down. Good oil pressure and clean oil is the lifeblood of a plain bearing motor. Even BSA made pump changes and relief valve changes in the later years so they knew something was not right. There is something that isn't quite right with the system and I guess we are spreculating to some degree on the cause(s).

Mr Mike

i've been unable to find any specs on this spring. i asked above and noone has replied... do you know what its proper length is? i can't tell how else you'd determine the proper function of the valve if not by reading oil pressure on the pressurized side or by determining that all components are within specs.

as soon as i get the chance, i'll try to do some pressure tests at the OPRV as well as at the switch orifice with the PRV installed. if i can get a decent reading, i may experiment with spring preload and see how it affects operating pressures.

Paul,
I understand your frustration. Perhaps you can stick a gauge in there and see what the maximum pressure is that you can make. If it is close to 50, leave it be.

Paul,

I've checked three different repair manuals including the original BSA Workshop manual for 1971 & later 650 models. They all state that the PRV is "self-contained and cannot be dismantled". They also don't list a free length for the spring like Triumph does so maybe the BSA PRV can't be disassembled. My 1971 Thunderbolt engine is dimantled and stored away so I can't get to the PRV at this time and can't remember if the above info is correct. I know there are discrepancies in some of the repair manuals so I don't always trust the info provided. I did find a spec sheet that I copied from an unk. source years ago that states that the spring length for the PRV that used the ball had a free length of .609" with a ball diameter of .3125".

It seems that once the oil gets hot, especially in OIF bikes that get hotter than dry frame bikes, the oil pressure goes down with multi-grade oil. Since I live in a moderate to hot climate, I've been considering a straight 50W to see hoe it works.

If you have already put an oil pressure gauge where the sending unit goes and getting only 5psi at crusing speed then you may have a leaking oil pump or your bearing clearences are suspect. The general rule of thumb for plain bearing motors is that you only need 10psi oil pressure for every 1000rpm. If you have anything close to that, you should be all right.
Ken

They usually state they are "self contained" because there are no internal parts available. You can still take it apart, inspect, and clean it. The spring on a ball type and piston type valve is very different. The ball type only has to lift off the seat to regulate, the piston type has to move the piston beyond the relief port. The piston type does not need a clean, smooth seat like the ball and the longer the piston, the less leakage before regulating.
Dry or OIF frame should not make any difference in the oil temperature. The dry frame holds a little more oil so it takes longer to heat up. It may dissipate heat a little better not being directly behind the motor.
I do not see any benefit of using a single grade oil. Once the motor heats up to operating temperature, the viscosity will be the same. The difference is when the motor is cold, single grade oil will generate very high pressure and could damage the pump, OPRV, or the bearings.

I don't think this is quite true. "Head Pressure Loss" through a pipe (or orifice, if it's sufficiently small, goes up inversely with the square of the diameter of the pipe or orifice through which it is flowing. The effect might not be noticeable going from a 1/4" to a 1/8", but I expect you'd see a BIG difference at something that's human hair sized?

Hydraulic engineers, front and center!

Lannis

The thing about a guage that I like is that once you know how your motor behaves eg how long it takes to heat up and pressure drop ect then you can pretty much spot it missbehaving realy fast off a guage.

I kind of use my guage as a comparitor rather than a strick measuring tool i look for consistency rather than readings, if you follow my meaning.

I dont look at it at idol after a run on the motorway....it only causes anxiety.

dont worry mine dose the same have run many thousands of miles like that at motorway pace 80 cold 50 norm motorway 50 to 20 use 50 monograde no oilfilter but an oil cooler