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

Hi Paul,


Uh-uh, I meant the connection of the line at the gauge. However, ...


Summat wrong with your gauge/set-up then? I've had o.p. gauges on two triples for something like 15 years, triples have been fitted with o.p. gauges as a regular thing since the mid-1980's and my T100 has a gauge. I've always assumed that a gauge bleeds off any air/gas automatically because, in all that time, I've never known any owner of a triple with a gauge ever worry about measuring gas pressure instead of liquid pressure.

Hth.

Regards,

Time for a hydrostatics expert to weigh in; I know we have one or two hanging about.

Say there are two identical lines connected to two identical gauges, with 50 PSI on the sensor end of the line.

One line is completely full of oil. One line is half-full of oil, and the rest of the line up to the gauge is full of air.

I believe the gauge will still read 50 PSI. The air in the line HAS to be at 50 PSI (subject to "head" losses in the line, which is true for both air and oil and should cancel out.)

Won't the gauge read the same in both cases?

Lannis

The difference is pressure be (density*gravity*height). Height is the difference in height between the partial full line and the full one.
The air above the oil would not make a noticeable difference in the reading. The air will stay there until the pressure causes the air to dissolve into the oil or the gauge is left below the source long enough for the air to creep out.

Methinks 50 psi is 50psi is 50 psi....that's what my Physics teacher told me. There might be a little time delay as the air compresses but not noticeable and if there is no flow (No leaks) there are no head losses and both gauges read 50psi It's a static system. It's like the home presure cooker at 10 psig. The presure is the same under the water as in the vapor.

A mechanical engineer who took fluid dynamics can give us something more official sounding.


Mr Mike

I don't think we need an ME to answer this one, nor an EE who studied a little physics.

Air trapped in an oil pressure gauge line will NOT change the reading.
A small diameter OPG line will NOT change the reading.

A small diameter line or orfice restricts flow rate, but not pressure.


now:
""last night i got a new diagnostic condition... complete darkness. i was warming the bike up in the dark, and noticed the head tubes glowing dull red!!!! i killed it, cooled it off, but had no choice but to limp it to my shop which was luckily not too far away. it was pouring rain and i had to be somewhere.
""anyway, i rode the whole way choked as much as possible to help cool the cylinders and it got there fine, oil pressure light staying off. took its temp as soon as i stopped, and it was 300F at exhaust side of the head. oil temps weren't too bad, at 125F or so. pulled the plugs and they looked sooty, which i would expect after choking it the whole ride."" Paul

Paul
There is no relationship between an oil cooler and red exhaust pipes.
Oil at 125F is stone cold and a cooler will not be good.
IMHO You need to let the oil get much hotter than that to drive moisture out of the engine and thin out to reach all lubrication points.

As for the minimum safe pressure for an A65, unfortunately I have no useful knowledge , let's get some more opinions. Where are those NOPG guys?

hey guys. first off, i agree that the gauge will ready properly regardless of the air in the line, but the air compresses at a different rate than the oil, which accounts for the lag in reading at the gauge. when i start it up, it takes a few seconds to reach the operating PSI.

SBoyd- i would expect that an oil cooler would help in warmer temperatures when the bike gets nice and hot and the oil is after all the medium cooling the engine. i'm running by bike in 45-55F temps right now.. i don't think i said that an oil cooler would have anything to do with the red hot headers, but i'll look back. i'm not sure exactly what you were referring to, but you quoted the bit where i was referring to keeping the bike cooler via choking the intake. fuel and cool air thought the intake valve does cool the intake valve and cylinder, and though it may not make for the best running condition, a rich mixture can keep an engine from overheating in a pinch.

in any case, i'm still getting next to no oil pressure at the gauge at warm idle, which worries me despite all of the comforting advice i've received. my sage machinist to whom i normally turn with such quandries just died a couple weeks ago, so i'll have to keep searching for answers. thanks to all for the help.

SBoyd sez:

"A small diameter line or orfice restricts flow rate, but not pressure."

An orifice in a "dynamic" system does in fact cause pressure drop. It is Hydraulics 101. And well understood and frequently used in hdyraulics for measuring and control.

As long as oil is flowing in the engine oil galleys, any significant restriction between the main galley and the gauge will cause a pressure drop.

BTW I am the founder of the NOPG Society. An oil pressure gauge is the worst device ever offered for installation on a BSA unit twin. Unless you can directly read the pressure at the base of the OPRV, which requires welding and machining to fit.

Paul,

Like many late unit twin owners who have fitted gauges and switches of unknown trip points, you are dealing with readings that will cause ulcers. Or cause you to go postal. Again, does the engine make noises that it is in distress? Does the engine generate shiny bits that are not a good thing? Have you switched to an SRM OPRV?

If the engine is not giving any signs of distress, sort your timing/carbs, break it in, then ride it like you stole it. A65's actually seem to like that treatment. At least mine do, Alex's do, Bonzo's do, Lannis' do, etc.......

Paul,
I don't know how to do that quote thing...but is this your quote that is in Sboyd's post?

"last night i got a new diagnostic condition... complete darkness. i was warming the bike up in the dark, and noticed the head tubes glowing dull red!!!! i killed it, cooled it off, but had no choice but to limp it to my shop which was luckily not too far away. it was pouring rain and i had to be somewhere.
""anyway, i rode the whole way choked as much as possible to help cool the cylinders and it got there fine, oil pressure light staying off. took its temp as soon as i stopped, and it was 300F at exhaust side of the head. oil temps weren't too bad, at 125F or so. pulled the plugs and they looked sooty, which i would expect after choking it the whole ride."" Paul "

Ths condition described sounds like severely retarded timing to me..... If the pipes close to the head were glowing red!!!

On the oil pressure...I'm in a different camp than others. I believe that these bikes ought to have in the neighborhood of 10psi/1000rpms. Check the machinery handbook. Whether that is consistently possible with todays parts and BSA's design I dunno. If they run with real low pressure I believe you are trading in long life. It probably won't go "kerblam" on you but it won't last like it should. I will admit that early cars (40ties and 50ties)didn't have as high oil pressure as cars do today, but the race guys and hotrodders of the period always put on gauges and had good aftermarket oil pumps on their stuff. As far as gauges, I'll wish I had one. If BSA put them on (like they should have) they probably wouldn't have sold too many bikes. Even the early aircooled VW's has warning lights and they work. I have a real good story on a VW oil pressure for another day.

Good Luck and stick with it. The bikes after 45 years are still a blast.

Mr Mike

My 2 cents.

Well I know what you guys are feeling. The insecurity of the oil pressure gage and light. It's like a that naggin' little voice in the back of your head that you have been trying not to listen to all these years. So if your are really worried that the oil pump is not putting out enough volume to keep the pressure up, then get the roller bearing conversion and have your pump supply just the big end bearings. And be happy. (That's what I intend to do).

BUT>>>

I know what a BSA sounds like when it doesn't have enough oil pressure. It is a really loud GaWD awful racket that another biker can hear from 12 feet away while riding. And I'm sure you guys don't have this because if you heard this cacophony of banging and chain knocking you would know that you have not got enough oil pressure. If I thrash the Firebird, the oil pressure light is full on at idle. But the motor sit there and purrs. It is not making sounds like it is coming apart. And there are no shineys in the oil.

What I would like to know is what Ger heard that caused him to tear down his engine (and discover all that damage).

Hello Ger? Maybe I'm wrong about all of this....

i hear ya Semper. the probem is, i don't know what normal clatter is for this engine... the only other pushrod engined bike i've owned was a '71 bonnie, and that was brief. i'm used to the cam chain rattle of 70's Honda fours. sure, i know rod knock or metal on metal when i hear it, but i' m still constantly listening to the motor and wondering if the sounds have changed.

after all, this engine was destroyed when i got it due to lack of oil pressure... i'd consider that reason enough to worry.

Paul...
"fuel and cool air thought the intake valve does cool the intake valve and cylinder, and though it may not make for the best running condition, a rich mixture can keep an engine from overheating in a pinch".

Your right about that for sure!....try running a motor way too lean and it will overheat big time, stands to reason that over rich (choke on) will be cooler due to the cooling effect of evaporating fuel, burning at lower temp ect.

I recon you need to listen to a few A65's running....you may not be comparing apples with apples. A65's do make a bit of a clatter compared with modern sewing machines on wheels. Normal "din" for an A65 isnt realy something easily described on a message board.


RichB....
" An oil pressure gauge is the worst device ever offered for installation on a BSA unit twin."

I guess that depends on what you use the gauge for. If you use it (as I do) to simply monitor for DRAMATIC changes like suddenly drops to zero while your riding along , it could tell you opv jammed, oil lines fallen off, pump is having a holiday, pump gasket has blown ect. I sure cant see how that is a bad thing. You will pick up a sudden drop in op much quicker with a gauge than waiting for the motor to let you know by exploding.

If however you use the guage as an "anxiety enhancer" I take your point.

today i flogged the [***] out of it up on my local twisty, and i can't say i'm much more comforted. on one hand, i rode for a good hour at high RPMs, but on the other, the indicated oil pressure- both at the gauge and the switch- read ZERO oil pressure through almost all but fairly high revs.

NOW...if i truly had no oil pressure at all, i'd have a dead engine right now, but i can't find a reasonable explanation for why the gauge reads 50 PSI cold, which is where the OPRv supposedly releases excess pressure, but is supposedly inaccurate once warm. ??? during this hard ride, the air in the pressure gauge line was visible, which means that there wasn't even enough pressure to compress the air and give an accurate reading. i will attempt to bleed the lines tomorrow, but with all due respect: i can't believe the folks that tell me to ignore the symptoms and just ride it. for those folks: will you back it up if the engine fails and i'm in search of something MORE than .060" over pistons, .030" under big ends, and .050" under main bush? all information tells me that i have poor oil pressure and that i'm lucky that it has done its job so far.

the engine was obviously less that totally happy under these conditions, but didn't give up the ghost.

Paul,
I only have one last ditch suggestion. Remove the OPRV and rig it so it can't bypass. A short piece of bolt instead of the spring and see if you have any pressure. Just leave the gauge abd eliminate that light if you have them both fitted. If you don't make pressure you need to visit that pump and its supply. If you have a filter it should be on the return side. I can't recall what work you did with the pump, but being a 71 it should have the bigger gears and may be cast iron.

You are getting some oil pressure or the motor would be finished if you flogged it real hard.

Mr Mike

Paul
Mr Mike has a good idea.
I had a similar problem on a Triumph and got this very idea from someone on this board and sure enough the pressure skyrocketed and the OPRV turned out to be the problem.
The length of the piece that you put in place of the spring needs to be just right.
On the BSA I'm not so optimistic, but I think it should be tried.
Good luck
>>sb

paul,
You'll figure out how to get the bolt the right length. That was my first method to test pressure because in my 66 A65L they have no port for a gauge. Later I soldered up the holes in one of the early OPRV's and made a test setup that I can check my pressure with from time to time. I was pleasantly surprised that I had decent pressure and I didn't do anything special with my early pump except put it together carefully. My bearings were all clearanced at .0015. Filter is on return side.

Good luck Paul. Keep us informed.

Mr Mike

"I can't find a reasonable explanation for why the gauge reads 50 PSI cold, which is where the OPRv supposedly releases excess pressure, but is supposedly inaccurate once warm. ???"
It doesn't seem to work the way you think, the OPRV may bypass at a particular pressure say 50psi, that's when it opens we think, however when its cold and open its usually got more than 50psi behind it because of the limitations of bypass flow and or thickness of cold oil. To get a normal hot engine pressure of 50 or 60psi means you will have 80psi or so cold everything being normal. I used to run higher than that looking for 75-80psi hot but that means 100+ when cold and perhaps over stressing the pump, which can spring it in the middle and spray oil out there.
Myself I would stretch the spring for 75-80psi cold and see what you have when it's hot. I'd do that before I'd lock the relief all together seeing it would have a H/volume pump.
Also being like a member of the oil pressure gauge society, I had an oil pressure gauge in a '94 Honda VFR 750 I had, it had very little pressure at idle when hot and the gauge almost worked as a rev counter, I think it had over 80psi at 10,000, the idea that the bypass valve maintained it at a constant pressure wasn't very true, it no doubt stopped it skyrocketing when cold but that was about it.
Modern cars seem to have smaller and smaller oil pickup gauzes we had a mitsubishi V6 with the oil light coming on all the time, at work and put a gauge into it-yep no pressure, so pulled the sump and declogged the pickup, what was interesting was 150psi, quized the mitsubishi guys and they said yea they run pretty high? So the point I'm trying to get at is the pressure bypass valve is limited in its control with all the variables they work under. It's not possible to make one give only 50psi cold and then 50psi hot as well, the hot pressure is more important, if you cannot adjust the relief to get most of it (50psi) at 3-4,000 it's probably dumping or bypassing oil somewhere.

""Myself I would stretch the spring for 75-80psi cold and see what you have when it's hot. I'd do that before I'd lock the relief all together"" Mark

Mark and Paul
This is for a test.
This is not a recommendation to ride the bike for any duration this way.
The point is to totally RULE OUT the OPRV and see what pressure can be made, hot and cold.

Mark's point is valid, but IMHO as step two.

IF the gauge SHOULD shoot up to 100 on startup, the engine should be shut off right then and the cheers begin.
If no gain is made, I guess the OPRV can be ruled out as part of the problem.

If any gain is made, spring stretching and substitution would be next.

>>sb

"Mark and Paul
This is for a test.
This is not a recommendation to ride the bike for any duration this way.
The point is to totally RULE OUT the OPRV and see what pressure can be made, hot and cold."
Yea I know, its likely worth trying I'm not against that, its just you don't want to see the needle doing laps of the gauge like when I put a H/volume pump in a rebuilt chrysler s/block with the relief valve spring jacked up on a nut I put in there for a bit of extra pressure :(:( I was young!!!, it blew the filter off, I was under the bonnet and my Dad was in the car when we started it, conversation went like this; Has it got pressure Dad?.....Dad??......Oh..It's just going round and round?? Then we had the oil thing happening Haha.
I've been thinking about it a bit and the fact that My A65 when its cold at 1,000rpm can have 60 or so psi yet when its hot in summer 20psi or very hot maybe 15 or 10 even, how much heat and oil thickness effects pressure, thats a massive variation and indicates how much faster the oil can get away when hot.

i'll try to rig up a pressure gauge at the OPRV over the weekend, or at least test it where the gauge is with the OPRV locked off. perhaps the OPRV is leaky and allowing hot low-viscosity oil to leak past the bypass piston even when not technically doing so? despite the apparently simple operation of the PRV (relieves excess pressure at 50 PSI regardless of oil viscosity), i think it is a little more complex than it seems. my Honda that i mentioned is a perfect example. i had almost the exact same conditions until i installed a stiffer spring in the PRV. now i get 70 PSI at cold startup and anything over idle, and 30 PSI at hot idle. on that engine i had ZERO indicated pressure warm, with the gauge installed directly at the pump.


i don't think i mentioned: i inspected the oil pump before re-installing it, and could find nothing noticeably wrong. the mating face was flat, and the gears looked healthy.

The std take off for the gauge is fine I endfeed my crank from that hole, its easy to stretch the spring by forcing the shaft of a small screwdriver between the coils, just do both sides or it will curve, and you can adj the pressure by just taking the cap off and spring out. If you lengthen it too much squashing it in a vice a bit will shorten it again.

Hey Paul,
What your are doing is simple to do and may eliminate a variable or possibly give you some more information. When I tested mine that way I pegged my 0-60 psi gauge immediately at anything over idle. As the oil heated up my idle pressure dropped till it seemed to stay at about 17-18 psi at idle and would be at 50 psi at 3500 rpms. I was satisfied, but it is entirely possible that after a long hard ride on a summer day that my pressure might be less. At this point I have to trust the system is ok for my needs. And to be honest, when I put the pressure relief back in I might get something different as I have no way to measure it without a port on my cases. I just believe that the BSA lubrication system was marginal from day one and that is what makes the endfeed so attractive. All the plain bearing motors of that period B25, A65, A50 seem to generate lots of complaints that point to marginal lubrication. Keep us informed and good luck.

Mr Mike

Mark sez:

"The std take off for the gauge is fine I endfeed my crank from that hole"

Some are fine. Some are not. I can't get pictures that show anything worthwhile, but I have 2 late cases that have virtually NO opening between the switch hole and main oil galley. The worst will barely allow a .015" wire through. But I have also seen late cases that switch cavity fully intercepts the galley. Would a .015" opening do your engine any good? I seriously doubt it.

I know for a fact that set of cases would always show low oil pressure once the engine was warm. And I ran the snot out of that engine, once the switch was disconnected. And that engine never once let me down due to an oiling problem. It just eventually got retired. And was tired

Paul need to: 1. Quit screwing around with a likely worn/scored/tired original OPRV and install an SRM OPRV. 2. Check his switch cavity. Little tough to do on an assembled bike, but possible. A light and some drill bits will tell him whether hsi cavity sideswipes teh galley or fully breaks into it.

i finally had some time to play with this today, so i did some tests.

first, i removed the spring from the PRV, and replaced it with a solid piece of steel round stock, shutting the relief off completely. kicked it over, and it pegged the pressure gauge. ok, the pump seems to do well cold.

then, i preloaded the spring about 1/4" and started it again. this time, the pressure was at about 80 PSI at idle, and would still go a bit higher if i revved it. i pulled the oil drain plug (was due for another post-break-in oil change anyway- no shiny bits, and the oil looked pretty clean still), and shortened the preload a bit while waiting for the oil to drain.

upon start up, i had 70 PSI at the gauge. got it nice and warm, rode it around a bit, and... the pressure dropped back down to zero at idle.

since i know my crank and rod clearances to be good, all i can think is that when the oil is getting hot enough, it is either creeping past the OPRV piston (which feels pretty snug in its bore) or there is another point of escape for the oil to cause the pressure drop. if someone can explain the physical reason why the gauge or location of the gauge would suddenly become faulty only when hot, please do.

i don't know what to test next without beginning to give a lot of money to SRM.

How was the pressure at 3-4000RPM when hot? Obviously oil temp is having a big effect. If the motor is new it could be running a little hotter than it might when run in more. Points of oil escape can be the 3 bearings, the bush being a little unconventional and less easy to check clearance when doing, cannot plasty gage.
But also the centre of the pump, if distorted or has loose bolts, as Rich points out thick washer on OPRV.

Paul,
A couple questions? (1) Did you put the piece of metal rod back in when the motor was hot to see if you had any pressure? Probably wouldn't change anything but I am just curious. I'll try testing my pressure again cause you got me thinking. (2) The first time I had a bushing bored the machinist missed the mark. When I got home it felt like the fit was too loose I brought it back and had him remeasure my crank with a micrometer and the bush with a dial bore gauge with me standing there. I was right and he redid the job at his cost. He openly acknowledged that it was his mistake. Are you confident that your bush has about .0015" (or close to it) clearance? (3) Is your idle real low? I used to set my ilde as low as I could get it but now set it at 1000-1200 rpms to make sure I have better oil pressure. If you can get 7-10 psi at idle and 30-40psi going down the road I would ride it. It isn't optimal by today's standards but should keep you riding.

Good Luck,

Mr Mike