The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: chotus52 on 27.06. 2017 02:30

Title: Oil Pressure
Post by: chotus52 on 27.06. 2017 02:30
Hi all, my 1955 Shooting Star is fitted with an oil pressure gauge. It shows about 20psi when cruising & drops to about 5psi at idle. Although the oil return "spits out" a bit at idle, there's a healthy return of oil into the tank anywhere above idle. Can someone tell me if this is normal pressure or at least sufficient pressure. Many thanks.
Title: Re: Oil Pressure
Post by: duTch on 27.06. 2017 04:23

 Tank return action is normal, but not sure about the pressure- I know it's not a high pressure pump,  but would've expected more than that ....*dunno*
Title: Re: Oil Pressure
Post by: KiwiGF on 27.06. 2017 05:23
Hi all, my 1955 Shooting Star is fitted with an oil pressure gauge. It shows about 20psi when cruising & drops to about 5psi at idle. Although the oil return "spits out" a bit at idle, there's a healthy return of oil into the tank anywhere above idle. Can someone tell me if this is normal pressure or at least sufficient pressure. Many thanks.

Ive not had a gauge fitted, but these engines do run low pressures when hot, there are threads on this that can be searched eg where even with the srm conversion 25 psi when hot was experienced, so I think your 20 sounds ok.

Some say don't fit a gauge as it's another thing to worry about (and fail!)
Title: Re: Oil Pressure
Post by: Black Sheep on 27.06. 2017 06:37
Ride a Norton 88 or 99 and you will find that the oil pressure can be 50 psi when cold, 0 psi when hot. There's a reason Norton stopped fitting pressure gauges early on - too many complaints. Yours sounds fine. Incidentally, some Norton owners get paranoid and fit high capacity pumps and double speed gears and then wonder why the top end over-oils drastically.
Title: Re: Oil Pressure
Post by: WozzA on 27.06. 2017 07:53
a couple of years ago Musky refurbished my old pump like new...
here's his results...

On cold start fast idle it was giving 325kpa and returning well to the tank.
After a few minutes warm up it gave 450kpa at 5000rpm
At 60mph (3250rpm) it showed 350kpa and at idle gave 250kpa.
Good as gold. 350kpa = 50lbs.
Title: Re: Oil Pressure
Post by: chaterlea25 on 27.06. 2017 11:09
Hi chotus,
oil pressure depends on lots of factors??
oil grade ?
pump condition?
PRV leakoff setting?
engine bush and bearing clearances?
How accurate is the gauge?

What is the reading from cold?
As the engine heats up the oil thins, also centrifugal force within the crank sucks the oil reducing pressure readings on the gauge

Answer the questions above and members will be able to offer a comparison if they have gauges fitted
I would expect 50-60 psi cold

Title: Re: Oil Pressure
Post by: coater87 on 27.06. 2017 20:00
 This is why Harley fitted an "idiot" light to their bikes.

 You set the light to trip at under 5 or 10 pounds pressure, its warns an owner something is wrong.

 Put a gauge on a bike and people worry all the time. *sad2*
Title: Re: Oil Pressure
Post by: Greybeard on 27.06. 2017 20:13
The 1929 Austin Seven that I owned for many years had a small black button on the dashboard that was held out by oil pressure. In the event that oil pressure, (4lbs hot) failed the driver was supposed to notice that the button was flush with the dashboard.
Title: Re: Oil Pressure
Post by: muskrat on 27.06. 2017 20:59
G'day all.
Lee is correct in that most idiot lights come on at 5-10Lb.
I like to work on 10Lb per 1000rpm up to 50Lb pressure relief valve setting.
Title: Re: Oil Pressure
Post by: Black Sheep on 28.06. 2017 06:53
Presumably cold Muskrat. A hot engine sees a big drop in oil pressure. Well, any bike I have had with a pressure gauge (1) has.
Title: Re: Oil Pressure
Post by: muskrat on 28.06. 2017 08:28
G'day Black Sheep.
At 60mph (3250rpm) hot my A10 cafe reads 350kpa. 25/60 Nulon oil Summer 20/50 Winter. Old original pump refurbed.
Title: Re: Oil Pressure
Post by: Sluggo on 28.06. 2017 08:55
I have not yet fitted one to a BSA preunit twin, so I cannot specifically say, But on any bike thats a rider or one of my keepers I am a big fan of a Oil filter and a Oil pressure gauge.  ( dont wish to get into an oil debate, but modern oils behave much differently than the oils in the marketplace back in the 1940s to early 1960s)  Used to be my online imaginary friend (Friends for 10 years but never met in person) was Gerry Bristow (RIP) who worked for many years for Duckhams and later Castrol oils and would insert some common sense into the many oil wars that would rage in online forums.

But I HAVE fitted Liquid filled oil gauges to many British bikes and I believe IMHO that it makes you a better owner and rider when fitted.   It reminds you to properly warm the engine, and to be sensitive to its needs with a very visual amount of feedback.   On a Triumph plodder I will service and reuse the standard Triumph plunger stock pumps. With anything hinting at extreme service or use,,I fit high volume 4 valved late style pumps, or the Morgo aftermarket pumps.
On all my chevys (and I used to build a lot of hot rod chevy motors) I always used without fail a Melling high volume pump.   Remember,, You want VOLUME,, NOT Pressure.   High pressure is indicative of high friction or resistance.  You want adequate film strength and appropriate amount of flow moving to cool AND lubricate. (Not TOO much mind you).

So, a Typical Triumph twin (500-650-750) or Norton Twin (500-600-650-750-850) With a modern 20-50 multi grade or (10-30w in winter) I would expect the cold pressure to peg around 70-80 PSI on startup and first few minutes (Which is why warm up and gentle use is critical),, Normal cruising speeds and high idles (momentary stops) would see avgs around 20-30 PSI, and when fully hot and on anything other than frigid winter temps at Idle barely ticking over a Triumph or Norton can flicker as low as 5 psi and typically around 7-8 psi.  Keep in mind a well sorted machine should be able to idle at very low RPMS.

I use a braided stainless line, or for stock appearances use a black fibre weave material for German and European cars for lines...  I run a Brass T fitting hidden and one side goes to the gauge, and the other to a sensor for an Idiot light.  I use off the shelf US industrial or commercial automotive grade sensors.  I typically pick one that triggers at 7 psi but you can buy any spec you want.  (Pressure point)  The gauges are typically aftermarket gauges for HD and other bike applications and pick one that goes to 100PSI as some only go to 40-60- or 80 and if you overclock them, they are never accurate again..  The one problem is they typically dont have back lighting. (I have a fix for that).   On a stock Triumph Bonnie or TR6 with Smiths tacho and Speedo they can be attractively mounted between the gauges and not stick out like a sore thumb.  Nortons we always typically made a Alloy plate out of 1/4" or 1/2" T6 plate.

For Triumphs I ran the gauges off the timing covers mostly except a few I tapped into the pressure relief valve ports,, For a Norton I ran double banjos both sides off the heads and ran the feed off the 2nd banjo.    For a  BSA Preunit twin I would have to carefully study where I would tap in,, But on my keeper projects, You bet,.. A oil gauge WILL be fitted.  I will work to make sure its not out of place or obviously intrusive.  Im okay with a hot motor and the idiot light flickering at Idle,, tells me its working.  But I know personally riding, I was glad to have the gauge, and I know of several shop customers back when I ran one who felt the gauge saved their motors.

It is beyond the scope of this forum, but worth thinking about,,, On many of these old plodders its well beyond anything to consider, but in a number of race engines and several Hot rod projects we used back in the 1980s and 1990s when I was more active,, There's a company called MOROSO and they supply the street rod and racing trade and they used to stock oil system accumulators.  These are std fair in a wide variety of aerospace applications and coming from that career field they were very familiar to me.  The Accumulators have various capacities depending on model (Volume) But how they work is one side of the accumulator is a charged chamber with pressurized Nitrogen gas.  The other side has a reservoir of oil and we plumbed these into the main oil gallery feeding the mains and rods.  At high RPMS,, High G cornering, or catastrophic oil loss (Holed sump) the accumulator toggles a pressure sender and Idiot lights go off to warn the driver, But you have a safety setting in place that if Oil drops below X value in pressure the accumulator feeds oil into the system so no lapses occur.  After exiting the chicane at the end of Turn 9 at PIR the oil pressure returns to normal from normal feed from the pump and accumulator recharges.  Again in the next High G event, instead of cavitating and air in the system the accumulator steps in again & again.  Oil related engine failures are almost unheard of, or non-existent.  If you spend a lot of time rebuilding engines, many people tend to be a bit paranoid about things like over temp and oil failures.

Ignorance is NOT bliss...  I have 2 friends who have crashed motorcycles because they were so distracted by noises or monitoring the engines/drivetrains they were not adequately paying attention to riding safely and both cases exited the road ways in a very embarrassing manner.  Both of these guys were very experienced riders and not their first rodeo.  I will admit to 3 different very close calls myself over the years as well.
Title: Re: Oil Pressure
Post by: Black Sheep on 28.06. 2017 10:27
Oil system accumulators sound like the aircraft hydraulic system accumulators I was familiar with in a previous life. One thing I haven't seen in old bikes yet is an electric oil pump to raise oil pressure and get oil circulating before starting. Now that's something worth considering. These are found on diesel locomotives and increasingly on RR Merlins. And probably Packard Merlins too. Particularly useful for engines that are started on an occasional basis for, as we know, most wear occurs on start-up.
Title: Re: Oil Pressure
Post by: Sluggo on 28.06. 2017 11:05
Hydraulics-pneumatics is very common on aerospace systems. There is a variety of them on many acft, or at least military types.  Most systems are designed to be triple redundant.  Gear blow down systems are the most common to my recollection. 

But a quick "The Google" search shows the Moroso accumulators are still being sold,,


a bit overkill for an old plodder certainly,  basic models has 1.5 US Quarts capacity, and they show one with a 3 quart capacity.  Theres also a video on that page illustrating how they work. 
I was thinking about this Ironically the other day for a Buell project I have for extreme lean angles and wondering about how I would make it work..  Getting off topic here but my XB series buells carry the oil inside the swing arms.

But a oil filter and a pressure gauge certainly would not HURT a BSA and the extra capacity would benefit the system.  I have recently advised a number of people on another forum about oil coolers and the need to do testing of your oil system.  On many old British bikes the oil cooks like crazy in the cyl heads around the exhaust ports with very high temps, but on many bikes the oil often does not get up high enough in temp, and oils need to be in the right temp zone to work correctly so, its critical to match your setup to what is needed.  Adding a oil cooler when your oil is under temp to begin with is foolish.
Title: Re: Oil Pressure
Post by: Topdad on 28.06. 2017 14:08
I can see it now, A10  rider dipping gracefully into a corner ,engine oil pressure drops, is instantly corrected by this system ,only for the rider to be drowned in SAE 30 as every single joint lets fly .  *countdown* *whistle*
Title: Re: Oil Pressure
Post by: chotus52 on 28.06. 2017 15:54
Just removed, cleaned & reseated the prv . Running Penrite 30 oil 20/w60. Oil pressure now 30psi cold reducing to 20psi at idle & 25psi when riding when warm
Title: Re: Oil Pressure
Post by: chaterlea25 on 28.06. 2017 17:53
Those figures are too low for my liking  *sad2*
PRV should open at around 55psi and feed oil to the cam trough
I would either get the PRV tested or substitute for a known value one