Author Topic: Oil pressure...  (Read 1081 times)

Offline cosmikdebriis

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Oil pressure...
« on: 09.03. 2012 19:51 »
As I understand it. Oil pressure is controlled by the pressure relief valve which is determined by the spring pressure on the bearing. (assuming the bearing is seated correctly).

So... It should be easy to increase pressure by simply shimming up the spring with, for instance, a washer.

However I would have though that when hot, oil pressure was probably not enough to open the ball valve at all?

Just wondered what peoples thoughts were on the bonuses and problems caused by increasing oil pressure and if anyone with a pressure gauge can confirm my suspicions that pressure when hot does not build up enough to open the valve?

Of course I appreciate that the pressure can be dependent on worn bearings etc.

Online bsa-bill

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Re: Oil pressure...
« Reply #1 on: 09.03. 2012 20:37 »
Well it is a pressure relief valve, designed to relieve excess pressure.
there are members here who have fitted pressure gauges so hopefully they will report there findings - it would be interesting to know what running psi is.
However they DO KEEP running and have done for decades so I guess the pressure is adequate (as RR would say)
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline BSA_54A10

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Re: Oil pressure...
« Reply #2 on: 10.03. 2012 01:27 »
Yes putting a shim under the spring would increase the running oil pressure.
Oil hot, oil cold the pressure would not change. The volume would but the pressure would not.
This has been a problem with replacement OPRV's as the washer fitted under the new units was thicker than the original which reduced the oil pressure.
As with all springs the spring in the OPRV should be replaced at regular intervals as the effect of heat over prolonged times will soften the spring.
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Offline alanp

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Re: Oil pressure...
« Reply #3 on: 10.03. 2012 10:56 »
Ok, here's an answer from an oil gauge RGS bike and SRM PRV.
Typically, at start up it'll show 70'ish psi, i.e the PRV setting and excess oil from the PRV is fed to the cam shaft.
During a fast 80'ish mph run of say 20 miles it'll be sub 50psi. i.e. the oil viscosity has fallen due to its hot temperature and the PRV stays closed. Oil is fed to the camshaft from the oil slinging around inside the crankcase.
I also run the engine with an oil cooler which maintains the oil a tad cooler and hence pressure a tad higher for those high speed runs.
It wouldn't make any sense trying to increase oil pressure by modifying the PRV since once the oil is warmed up it won't reach that pressure anyhow.
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Offline cosmikdebriis

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Re: Oil pressure...
« Reply #4 on: 10.03. 2012 13:47 »
It wouldn't make any sense trying to increase oil pressure by modifying the PRV since once the oil is warmed up it won't reach that pressure anyhow.

Yes, I'd kinda assumed that but am now concerned at lack of lubrication to the cam if, as you say, it is only fed by oil thrown around inside the engine when the PRV is closed. Doesn't strike me as an ideal situation but I suppose it's been working okay for many years now.

Anyway, thanks for the explanations guys. Unfortunately I am blessed (or cursed) with wanting to know how things work. Have been since a kid so there's not much hope of it changing now.

Online bsa-bill

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Re: Oil pressure...
« Reply #5 on: 10.03. 2012 14:40 »
Yes the cams do wear in time, they do however run in a through that contains enough oil to ensure the lobe dips into it when it comes around.
and although they wear I have not heard any stories of them picking up
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline dynodave

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Re: Oil pressure...
« Reply #6 on: 18.03. 2012 16:17 »
The oil pump put out a volume of oil based on the rpm. At low rpm the oil leaks out the various orifaces faster than the pump puts it in. Oil pressure is higher when cold and viscosity is high. As the oil heats up the viscosity drops and can leak out faster...pressure goes down.
Now the leakage oriface are basically fixed regardless of RPM, but oil pump displacement volume increases with RPM.
when pressure rises and eventually exceeds the relief valve setting it opens and "attempts" to vent excess pressure. It definitely can't vent enough with cold oil and the pressure goes way up at a low RPM. when hot it needs a higher RPM to get to the vent pressure.

It is very unlikely that shimming the OPRV has any pressure effect to low RPM running. It is only once the pump out put exceeds the bleed off of the orifaces does the OPRV do anything. Oil temp and viscosity are the controlling factors... which do change drastically.
I see the OPRV as an attempt to moderate severe overpressure when cold...attempt yes...entirely sucessful.... no way. I have run a gauge on my norton for decades and this stuff finally sinks in. I am very confident my A-10 is not different in any way. *beer*
dynodave
61 Gold Flash* 63 Super Rocket* 63 RGS