Oil pressure and low power

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Ian Grace
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Oil pressure and low power

Post by Ian Grace »

This morning I received an e-mail from Peter Hills who has returned from South Africa for the English summer (apparently, he's an optimistic sort of fellow!) - via chasing gorillas in Rwanda - I'm sure there's another good story there!

Anyway, he tells me that his '29 tourer is giving 120 psi cold and 80 hot, and also remarks that - well, here it is in his own words:

"A friend in cape Town (vintage car guru) said that I am wasting power with my oil pressure at 120psi starting cold and 80 when hot. I use Penrite oil. He says I should just use a modern SAE30-40 oil as the engine will be happier. What are your views?"

This immediately put me in mind of an article by the last David Bick - a vintage engine guru. Here's what he had to say on the subject back in M 113:

"Now that vintage cars are so prized, like old cottages in the country, we often find that the first thing that a new owner undertakes is a thorough restoration. And usually this involves a more or less total rebuild of the engine. For it is always assumed that a reconditioned unit must be better than an old one, and certainly no specialist firm out for business is likely to deter you. And regardless of the engine’s true condition, it is not unknown for the client to be hood-winked into a total overhaul – crank grind, re-metalling, rebore, new pistons and all, on the basis that the job could not be guaranteed without one. Often, the results are disappointing, not to mention the cost. Oil consumption is a common pretext, and perhaps sundry miscellaneous noises in varying degree. But what is generally forgotten is that few vintage engines ran with a Rolls-Royce silence, nor ever approached modern engines as regards oil consumption, most of which seem to use none at all. Indeed, such a goal would then have been considered not only unattainable, but undesirable. By present-day standards, all vintage cars drank oil, and when the Rolls-Royce 20HP model came out in 1922, a consumption of 1,000 miles per gallon was considered remarkably low. And some sleeve-valve Daimlers could only manage 400!

The standards of today are mainly due to tighter and more accurate clearances in the moving parts and better piston and ring design, all of which might be applied to rebuilt vintage machinery, but only at a price. For although you are quite likely to end up with a quiet engine, it will probably be sluggish, run hot at the least provocation and be heavy on petrol, to the extent that the extra cost of fuel easily outweighs the saving on oil. It is like driving with the brakes on which, in effect, it is.

However, you will be told that “all rebuilds are like this, and things will be much better on running-in, old boy”. But although this for long held true, the story is very different today. Largely due to imported oils, additives and filtration, engines virtually never wear out, and thus it follows that they do not run-in either, for running-in is simply a process of gradual wear. A man well known in the motor trade told me he had recently taken a BMW engine to pieces and the honing marks were still visible in the bores after 100,000 miles! No wonder Peter Lilley’s 14/40 MG is nice and quiet but still tight after years of extensive motoring, and still is only doing 20 or 21 mpg. (in this context, I am told that Castrol sell and old-fashioned ‘straight’ oil which may be ideal for running-in, but no more details are to hand.)

Unlike their modern counterparts, vintage engines do not have the power to spare for the inevitable higher friction which results from tighter clearances. The late Freddy Dixon, the ace Riley tuner, said “take three thou off everything” if you want performance and economy. If a Morris engine is free, with the plugs out you should be able to turn it over on the handle with one finger even when stone cold. Some years ago when I rebuilt my 1929 Cowley UF 5170, bored out to 70 thou to suit Renault pistons, I specified an extra 4 thou clearance in the bores. The engineer was horrified, but the car went splendidly from the start, often does 30 mpg at 50 mph and, much to my surprise, uses very little oil. It is, however, quite noisy when idling, but you can’t have it all ways. The choice is yours!"

I know of several owners over recent years who have spent a fortune restoring their Minors, then sold them not long afterwards because of their disappointing lack of power. I think another reason which is particularly the case with OHC engines is that owners are afraid to rev the engine, so never get the higher torque that these high-revving engines can deliver. The more gently you drive them, the worse they perform.

What does the team think?
sv4670
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Re: Oil pressure and low power

Post by sv4670 »

Interesting stuff. To return to the original question about oil pressure though; too high a pressure is actually a bad thing I understand. I believe I have read somewhere that that this can "scour" the soft bearing material - in effect power wash it away!. Is the pressure reading taken directly adaject to the pump delivery pipe or further downstream? The pressure will drop off gradually at successive pressure tappings.
I think we need a diagram of how the oil is pumped around the engine to be able to make an informed view.
Trevor Wilkinson
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Re: Oil pressure and low power

Post by Trevor Wilkinson »

As the oil is not compressible the pressure will be the same unless it is restricted as in the feed to the ohc.
Simon
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Re: Oil pressure and low power

Post by Simon »

I presume that he has checked that the pressure relief valve is free and not seized up as the car has not been used for some time. What grade of oil is being used, I use a straight 30 and the valve blows off at about 80 psi cold.
Ian Grace
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Re: Oil pressure and low power

Post by Ian Grace »

I will ask him about the relief valve. And I'm not sure how he knows he's getting 120 psi, as the gauge only goes up to 100. He's using Penrite, but I'll ask him what grade.

I wish I had this problem - mine always seems to be lack of oil pressure!

I've had lots of Minors that gave a miserable 20 psi if I was lucky at hot idle and about 35 to 40 in the cruise. But I only ever once ran a big end - racing an Austin 7 through Hyde Park in the early hours one Sunday morning - but that is a story for another day! The interesting thing about that little excapade was that I had the crank, beartings and rods done, but could never get any serious oil pressure from it afterwards. I tried absolutely everything, including fitting three different oil pumps, all to no avail. Never did get to the bottom of the problem.

But then we have the early Austin 7's with their 'spit and hope' system and about 2 to 3 psi oil pressure that run fine, so I'm wondering if 15 to 20 psi is really a bad thing, unless of course it indicates that the bearings are truly shot.
plj
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Re: Oil pressure and low power

Post by plj »

The morris 8 engines used with the generator sets in Centurion tanks had a modifies pressure relief valve set to 100 p.s.i. didn't seem to do them much harm. The ex-military engine fitted to my 8 tourer starts at 100 dropping to about 55 when hot, I think anyone who has followed it will agree it goes rather well.

Philip
Ian Grace
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Re: Oil pressure and low power

Post by Ian Grace »

Thanks Philip. My first Morris was a 1937 Morris 8 tourer which had been fitted with a 1946 Wolseley 10 OHV engine - XPAG, same as in the TA I believe. That went rather well too! 8)
martinng
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Re: Oil pressure and low power

Post by martinng »

I seem to remember that high oil pressure can be a sympton of a blocked oil metering pin in the OHC engine. This of course can starve the cam gear of oil. A check witht the rocker cover off to see that the oil is gettng through to the rockers might be an idea.
I'm glad to say that with my recently rebuilt(2500 mile ago) enginethat when hot I get 50 psi on tickover and 90ish when running with no real problem with power. The main contribution to sluggishness was in fact badly adjusted and binding brakes, and now that's fixed I can pull up all but the most severe hills in top. I guess that the engine was rebuilt sympathetically with a view to maintinaing the traditional tolerances so that even though it had a new Pheonix crank and bearings etc, it does not seem to suffer from unusual tightness.
Martin
Ian Grace
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Re: Oil pressure and low power

Post by Ian Grace »

This from Peter Hills today:

"Actually, the OHC engine I acquired was standing for about 20 years. When we stripped it my father (a motor engineer) told me not to bother having it bored, or change the rings or indeed have the bearings remetaled. All we did was to get Mike Dowley to update the head with sealed cam drive and bronze plummer block at the back end of the cam pivot shafts. Of course the engine may have been ‘done’ before but I realised they had a problem with severe vibration. The flywheel mating surface to crankshaft had been plastically deformed (someone hammered it), this was detected when we tried to balance the assembly. I then had it skimmed and after balancing the complete assemble to F1 standards and weighed everything else to identical amounts the engine was assembled and started easily and always has.

From memory I'm using around SAE40 and no the pressure relief is not stuck, the pressure has been like that since my rebuild in 1992. However, I do, from time to time revolve the relief pin. My gauge goes above 120psi so perhaps I have an M8 gauge version? I did buy a complete panel with gauges many years back.

I am yet to fire up the engine since our return from Rwanda and do not expect any issues. First I liberally oil the cam shaft, then manually turn over the engine less plugs. Then I run the engine (no plugs) until the oils pressure is up for say 2 minutes. Radiator is filled with fresh water and run through a while. Plugs are returned, switch petrol and ignition and some choke and it usually fires up right away. Thats my process. Oh yes I have a CETEK battery conditioner/charger and it does an excellent job maintaining the battery."
sv4670
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Re: Oil pressure and low power

Post by sv4670 »

Could the gauge be wrong? Might be worth trying another just for interest. :wink:
PeterWHills
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Re: Oil pressure and low power

Post by PeterWHills »

Returning to this old post of 2014, I have something more to add. First as originally an Instrumentation Engineer, I can confirm my pressure gauge that has a top range of 160psi and is in calibration. Two months back I decided to flush the engine oil; I used WYNN'S Flushing additive additive according to instructions. I then dropped the sump and removed any old oil but I was pleased that there was no 'sludge' present. On the long drive London to Bath the oil pressure quickly dropped to 80 psi then 60 but settled at 40psi where it had never been so low yet the car went very well. This suggests that some lubrication channels have been further cleared? Fuel consumption is over 40mpg and my car cruises at 40 to 40 mph.

When I restored the engine in 1991 I placed a huge emphasis on clearing out the lubricant channels, particularly the crankshaft. I was confident that every particle of debris had been removed. I then placed a rare earth magnet (very powerful) in the Filter Basket and each time I change the oil there is a paste of debris (probably less than 10 micron) but also I noticed some wisps of fibre that metal particles had agglomerated around. These fibres must have come from 'mutton cloth' or other cotton material used when cleaning the engine parts. This should be a warning to all when using cloths to clean at overhaul.
PeterWHills
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Re: Oil pressure and low power

Post by PeterWHills »

PeterWHills wrote: Fri Nov 02, 2018 6:05 pm Returning to this old post of 2014, I have something more to add. First as originally an Instrumentation Engineer, I can confirm my pressure gauge that has a top range of 160psi and is in calibration. Two months back I decided to flush the engine oil; I used WYNN'S Flushing additive additive according to instructions. I then dropped the sump and removed any old oil but I was pleased that there was no 'sludge' present. On the long drive London to Bath the oil pressure quickly dropped to 80 psi then 60 but settled at 40psi where it had never been so low yet the car went very well. This suggests that some lubrication channels have been further cleared? Fuel consumption is around 30 mpg and my car cruises at 40 to 45 mph.

When I restored the engine in 1991 I placed a huge emphasis on clearing out the lubricant channels, particularly the crankshaft. I was confident that every particle of debris had been removed. I then placed a rare earth magnet (very powerful) in the Filter Basket and each time I change the oil there is a paste of debris (probably less than 10 micron) but also I noticed some wisps of fibre that metal particles had agglomerated around. These fibres must have come from 'mutton cloth' or other cotton material used when cleaning the engine parts. This should be a warning to all when using cloths to clean at overhaul.
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