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Topic review (newest first)

2019-08-02 18:08:19

Oil gauges have the nickname,the "worry gauge".Ted

2019-08-01 22:07:17

Mine's a '36 light 12/4 with white metal bearings, rebuilt about 2000 miles ago.  i get 30 psi at 40 mph, dropping to 25 on a long run.  Not too many miles ago I noticed a sudden drop on oil pressure to 20 PSI.  I took the sump off and lay on my back gazing up for a while, inspecting each part closely and eventually noticed a hairline crack in one of the copper pipes.  I had a spare, fitted it and it's been fine since so it's not always the obvious thing.

Charles Lacey
2019-08-01 15:32:52
5750_David_Ralph wrote:

It could be that the oil pressure gauge is under-reading. You could try another pressure gauge. It doesn't have to be the correct Austin gauge. Any gauge with the correct pipe fitting on the back will do to test the pressure.

That's a thought.  Calling on my metallurgical knowledge which is now very rusty (sorry, pun unintentional) and assuming that the curly tube inside is made of brass, it may have hardened as a result of many years' use and consequently be under-reading.  There are several cheap-and-cheerful OP gauges on Ebay but I am not certain of the correct fitting for the pressure pipe - is it 1/8 BSP?

However, good news!  Acting on a friend's suggestion I replaced the ball and spring of the relief valve and the pressure has gone up to around 25PSI which I take it is adequate, given reasonably clean oil.

Again many thanks for all the helpful advice and suggestions.

2019-07-30 22:32:42

It could be that the oil pressure gauge is under-reading. You could try another pressure gauge. It doesn't have to be the correct Austin gauge. Any gauge with the correct pipe fitting on the back will do to test the pressure.

Charles Lacey
2019-07-30 20:55:23

Thank you for these helpful replies.  The engine doesn't seem to be burning oil in any significant amount - the exhaust is clean and the plugs show no sign of soot.  I don't have the facilities to strip the engine, so I'll keep going for the time being.  I will try re-facing the oil pump plate, though.

2019-07-30 17:37:18

In my view 21psi on a white metal engine is a bit low but if the it runs well, does not knock and does not eat oil, I would carry on using it. In my 10 experience, main bearings do not seem to break up like the white metal big ends can.
The oil pump can easily be checked by removing the sump and the pump and checking the internal wear on the end plate after removal. This can be reduced by filing the brass end plate and refacing it using grinding paste on a bit of float glass to eliminate the scoring from the gears. At least you would know the pump is as good as it can be and reduces the end float. Screw the relief valve in further to see if there is any improvement. It will not do any harm.
10psi on tickover is OK. On a shell-bearing engine I would expect higher than 21psi.

2019-07-30 17:27:40

Hi Charles,
When we were young we were taught that Oil Circulation was much more important than pressure. Of course you'll get good pressure if there are tight clearances at all your bearings and in your oil pump. However, as Tony Mealing recently noted in an answer, he has an engine that just keeps going satisfactorily with consistently lower than expected oil pressure.
Using 20w/40 oil, my 1936 New Ascot shows a hot running oil pressure of about 20 lbs/ There is no blue smoke from the exhaust and no bearing noise. It has been like that for over ten thousand miles.
I just clean the sump and strainer and change the oil every 3,500 miles and use the car more or less every day.
I don't worry about it and neither should you.
Peter C. [6515]

David Johnson
2019-07-30 14:33:50

I completely rebuilt the engine on my 1935 10/4 last year. It was fitted with shell bearings some time in the past but where they must have been well worn a previous owner had fitted shims between the shell and the con rod + bridge to distort the shells so the mains ran quietly. In other words a complete bodge. The "cord" rings on number one piston were all broken and on number two the top ring was also broken. The engine still ran and delivered 30 psi even when hot. I still don't understand it but these engines seem to just run and run. it was only when the car starting putting out a smoke screen from the exhaust that I started the rebuild.

Charles Lacey
2019-07-30 10:16:09

The oil pressure on my Ten hovers around 21psi when running at normal revs (say 35mph in top gear).  When the engine is thoroughly warm it maintains about the same pressure, but drops to around 10psi when idling.  It's using Castrol XXL SAE40 oil.
I've screwed in the relief valve spring one full turn, without making any noticeable difference.
One odd thing is that - again when the engine is hot - I drop down to about 25mph in top the pressure increases slightly, to perhaps 22 or 23psi.
I take it that either the oil pump is well worn and/or the main bearings are getting a bit loose. 
However, is bearing failure likely at this sort of oil pressure, or can it be safely run at moderate speeds?  I wouldn't thrash it anyway!

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