A65 oil pressure collapse

[Shedman]

On starting up oil pressure is 65-70lbs this settles when warmed up after a couple of miles to around 45lbs at 4000rpm and stays that way for about 15 miles but then drops to around 25lbs and only 10lbs at tickover. It has good quality oil in and i would have thought that the engine would be up to normal working temperature well before 15 miles.anybody got any thoughts on this?

[ChrisG]

Those pressures sound quite good to me. I would only call it a collapse if the oil pressure light came on all the time. As the oil warms up, it gets thinner and the pressure falls.
On my A65 OIF I had the problem for years where the light came on at tickover and sometimes took a while to go out when starting off. I thought all pressure switches were the same but they aren't! I looked up one of the service sheets in the members section (I cant find it now) and this said that the A65 should be one where it lights up when it gets below a paltry 5psi, I obtained the correct one and I use straight grade 50 oil, and the problem has gone away.
I have recently taken the head and barrels off  10,000 hard miles after the last time they came off and there is no play in the big ends and no wear on the bores. So, the oil pressure doesn't seem to be a problem on mine.
As long as the sludge trap has been cleaned out and the oil can get to the big end journals then everything should be fine!
Hope this allays any fears you may have.
Chris

[JulianS]

This is the Service sheet the Editor refers to.

[ChrisG]

That's the one Julian! I had in mind it was in the 1971 or 1972 section. I did look back to the 1970 and 1969 but should have gone one further.

Anyway, I bought a new one from my local Motor Factors a couple of weeks ago and I needed to go through his Inermotor catalogue to select the correct one. Make sure it has a small hexagon portion of the body similar to the one illustrated as there are some where the hex is at the outer portion and they wont clear the outside of the crankcase.
Chris

[Bess]

Hi,
     This is worth a read.....

Best wishes...

[Bess]

Hi Shedman,

Out of interest did you solved the issue or are you living with it?

Best wishes...

[Shedman]

Im living with it at the moment i have allready changed the ball and spring in the relief valve but that made little difference.I may well be overthinking this but my other a65 makes 20psi more and falls very little no matter how long i ride so for now ill just see how it goes

[JulianS]

You could try the later PRV with piston rather than a ball. The piston type flutters less.

Are you happy with the accuracy of your instrument.

BSA published a service bulletin (in the USA) dealing with testing oil pressure, shown below.

[Bess]

Hi Shedman,
                   If your pump is worn some oil will pass from the discharge side to the suction side within the pump body. This happens more if the oil viscosity is lower (when hot). At higher pump speeds the loss is is a low percentage of the total flow (hence high press) but when idling it's a greater percentage (hence low press). I guess BSA were happy if you had over 5 psi at idle and the pressure switch specified illuminated the warning light below 5 psi.

Overall it's the flow you want. When the oil is cold you get a greater pressure with enough flow, when is hot you get the same flow but a lower pressure. I keep meaning to set up a flow measuring system on my A65 as I have similar oil issues as you. I have a oil gauge on mine, in the line I am going to fit a tee with a valve to measure the flow for say 15 seconds or so.

Best wishes...

[Bess]

Hi,
    An update on my low oil pressure. I did refurbish another old pump, fitted and the pressure decreased so ordered a new pump, prv and gauge.

Today I changed the oil pump for a new SRM pump and the pressure increased from 15 to 30 psi. I then fitted a new SRM PRV and it increased to 35 psi. Finally changed the pressure gauge and it is sitting just over 50 psi no matter what revs the engine is doing. I will run the engine on a long run when I permanently fit the gauge.

Seems all the components in the oil system were effecting the oil pressure.

Best wishes...