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Oil filter and circulation system in Vintage Bentleys

The focus of our January 2014 newsletter was whether the oil filter and circulation system on an early 3 Litre (or any other Vintage Bentley) be maintained as original or can it, or should it be improved or replaced? Read this article below.

This topic has generated significant interest and we are updating this page constantly with feedback received from our readers:


Julian Ghosh - Feb 11, 2014

Dear Robert, I know we are united by a common language but notwithstanding that, it is easy to make assumptions.

Placing a modern filter in to the main oil gallery will result in a considerable pressure drop due to the ensuing restriction. No modern car system does this but instead filters the relief flow from the pump. Clearly the flow rate of modern pumps is higher than those of 90 years ago but engines nowadays require more flow to cool the oil because one can run at
continuous high speed more readily. We have an arrangement whereby the oil to the overhead gear on a Bentley engine only is filtered,which appears sufficient, since the oil is circulated so many times.

Apropos filters on carburettors; please bear in mind that there is a secondary function, which is to silence the intake roar. Hardly significant on a Bentley but good reason to fit such things on modern cars. I guess you will not have any evidence to support undue engine wear after 90 years on a Bentley engine due to lack of an air filter but needless to say fitting such a device will alter the mixture strength


Christopher Jonas - Feb 11, 2014

Dear Robert. Thank you so much for the brilliant Newsletter. I read every word with interest! The most fantastic engineer is Steve Wynne, so anything he says or writes is golden info. Many thanks again.


Chris Tutton - Feb 08, 2014

Air-Filters on Carburetors
I cannot understand why anyone should be in any doubt over the non-use of air-filtration at the time in motorcar development 'we' seem to be concerned with.

S.U Carburetor Company supplied their air & fuel mixing devices, to several makes of motorcar over many years during and after Bentley Motors. Riley, MG, Bugatti, Wolsey to quote known names, certainly never used air-filters. The Twin Slopers used on the Bentleys were never intended in any case for air -filtration. Any one who has worked in tuning and air induction with combustion engines, will know that any filter added to an air-intake, impedes air flow, yes, even today, the same rule applies. 'Rams' are used to improve air-flow, and that is before we talk about supercharging the air-induction.

Leave the Bentley-Engine alone, it was very well designed by his Master and does need changing because 'we find it odd'!!!


Gregory Porter - Feb 08, 2014

Robert, No W.O. Bentley came with air filters. The covers on HG5 SU that were fitted to 4.5, Speed Six, Blowers, 4, and 8 litre are flash bowls. They help prevent fire. The modern air filters that can be fitted are very good. My dad fitted K&N filters to his 4.5 before it taking the car to South Africa in 1995. In all reality you really don't need air filters on a 3 Litre. I would recommend them if you are going to do some serious rallying, or if you are going to race the car.


Dave Lyons - Jan 05, 2014
Many thanks for sending me your informative newsletter. I am the lucky owner of a late 1930 4.5l genuine short chassis (AD3651). Still with its original Harrison open body. It has been restored and refurbished a number of times and is currently in very good condition both mechanically and bodily. I do indeed have a cartridge oil filter system which works very well. The car is fitted with a D-type box. We are based in Cape Town South Africa, where there are very few cars. Your cars for sale column gives a good indication of the value of these cars. I would imagine an unmolested car like ours may attract a premium.

Many thanks again for your input. Have a great 2014.


Chris Tutton - Dec 30, 2013
My late father Eric Tutton did have some mechanical problems with the cars (XU 3281 / KD 123). However, in your latest newsletter, you refer to oil lubrication problems with the 3 litre. I have to say that there was never, I repeat never, trouble with the lubrication of those engines! Even with the greater-stressed 3/4 1/2 that we ran did that engine suffer the complaint that you mention! Boiling water and cross-shaft gears maybe.

Yours, Chris Tutton


Whit Ball - Dec 28, 2013
Good evening and Happy New Year to all,

Oil is always good to have on start up. I fitted an Accusump 3 quart 'Pre-oilier' to 946 in 2000, the engine was finished just barely (isn't that always the way?) in time to load on the boat for the 2000 BDC tour to Italy and back — plus the Yanks did an early bit in France to start it all off.

You can find Accusump listed for sale on most USA race car sites, as they have saved many an engine while on the track. Basically it works this way. Hook up the one tube to the largest oil inlet you have (left rear of block as I remember it) mount shut off valve AT THE ACCUSUMP INLET, this should be a 1/4 turn valve and can be hooked to a pull/push cable [or they can supply an electric open/close valve and a toggle switch will work it). Fill the engine with oil, run it, till a little warm, with zero pressure in the tank (rear mounted tire fill stem and pressure gauge you will be familiar with by now) add 2 quarts to the engine oil and run it again, when warm, open the valve — watch the cars oil pressure gauge — it will drop, rev slightly to bring it back to your normal operating pressure, the rev a bit more, and if the gauge shows more shut the Accusump valve.

You now have either 2 or 3 quarts of oil in the pressure tank (still with zero pressure) and if you bought a 3 quart unit you are now that quart low in the engine. Refill the engine if needed. Put air hose to the tire fill on the back of the tank, careful — you want about 20 pounds more than your normal shown pressure only. Check to see that all the oil is inside where it belongs, and you are set to try it.

With all normal starting systems set to just push the button for start (sorry, my Smith's starter pull knob is still on the dash but for decoration only). Open the valve, watch the dash pressure gauge and give it a moment past the normal full pressure showing and you have an engine full of oil, so hit start, you can most likely watch the gauge go down, and before it bottoms out, come right back up. KEEP THE VALVE SHUT.

When your temps are all to normal, again rev it just a bit for higher for a bit of extra pressure, and open the valve, when the pressure shows the same level again, shut the valve.

Takes more writing than work, and I think it is well worth it.

For the money I also added a full flow [Fram HP-1] racing size openings, [bigger openings=smaller pressure loss], I did not put a back flow [one way flapper valve] in the line, tie it in on the engine side of the filter, and be sure the feed hose for the filter does not go downhill all the way back to the sump — or the hose and part of the filter will be empty, and take a good bit of oil just to get any to the engine.

Another way, would be to get an electric diff/trans oil cooler pump, tap into the sump, feed into the block inlet above the pump, a bit slower, a bit less pressure, but there will be enough oil to do the lube it needs to.

How long would my new engine have lasted without it? Don't know, but I haven't done anything to the insides now for 13 years, and still it almost takes a 4.5L with a 'fan' to pass me — bet someone will be wanting to test that in Maine this May. Bring it on.

Hope this was of interest.


Steve Wynne - Dec 28, 2013
First thank you for your news mail which I very much enjoy receiving. I am writing in response to your first item regarding oil filters. I too don’t like the look of the modern spin on conversion, so I have constructed my own, which works well.

I rebuilt my engine some 205,000 klm ago and fitted the filter then. It comprises of 2 Mercedes Smart Car filters on top of each other, which nicely fit in the original housing, they are a little tall so I made a simple brass cap extension, which I think looks fairly period. Now before anyone makes a comment, I know the oil is flowing through the filter in the wrong direction, but it makes no difference as the filters are very sturdy, and as I say in 205,000 klm, mine have shown no problems. Another good feature is unlike a cartridge you can examine the filters for particles which will warn of any on coming problems. The filters as easily available and cheap as chips, so if your engine is old (not just rebuilt) I would suggest changing them every 1,000 miles for the first 5 times, and if they remain reasonably clean and unclogged, then like me 5,000 will be OK.

Here are pics of another couple of good mods which I have done.

Click for larger view

First is the water pump, which as you know with the string gland either leaks or, or worse, loads and wears the cross shaft. 2 sealed bearing 28mm X 15mm X 7mm + a lip seal 28 X 15 X 8 just fit in the housing without any mods. My shaft was a little worn so I fitted a thin sleeve, which is a simple job even with the most basic lath. Cost about $30 all in. Just started to drip last week, so next time will change at 200K not 205K! Other good mod was fitting rubber tips to my float needles on Brass Sloppers. Amy, my 100 mph car, used to do around 18 mpg (UK gallons) After the mod I now get 25 mpg.(35% improvement) I could always smell fuel when traveling at a bit of a lick, so put it down to vibration making the needles dance and flood. You buy a set of modern SU float needles and jets, thread the needle, drill and tap the brass one, also drill and tap the float bowl, and screw in the jet. Of course you have to reset the needle height, which is simple.

That’s my two pence worth, and if any one wants more information they can mail me direct. If it is of interest, my background is I trained as a Maintenance and toolroom fitter, and later ran a World Class motorcycle race team. I have rebuilt quite a few Bentley engines for friends as well as my own.

Good luck and keep up the good work.


Sidney Farnsworth - Dec 28, 2013
We installed a Filter on our 4 1/2. If memory serves me correctly the biggest concern was to ensure the oil pump was adequate to maintain a proper flow through it. We use strictly 50 weight non detergent oil, as difficult as it is to obtain sometimes.


Roley Fraser - Dec 28, 2013
Robert, the whole subject of mods comes up every now and then. In my opinion, it depends whether you want to keep originality or to have a car which is easy to drive and maintain.

When I owned YM 57 I had several mods: Hydraulic front brakes, electric fuel pump, overdrive, coil ignition a 16 gallon tank and an alternator. These mods were made for a car that was easy to drive for long journeys, and a great deal less worry about things going wrong. I never bothered too much about originality as I never looked on the car as an investment — but as something to enjoy. I believe that since I sold her YM has been rebuilt to be as near original as a 3/4.5 "bitsa" car can be, so presumably is being treated as an investment — more's the pity!

With all good wishes for 2014.


James Medcalf - Dec 28, 2013
Dear Robert, These pictures show early 3 lt Oil Filter which I modified some 30 years ago. You have to turn the filter 180 degrees in order to get the oil from pump to the outside of the filter element.

Click for larger view

The square sealing ring that comes with the early Land Rover Oil Filter Part Number RTC 3183 can be fitted into the filter end cap. This modification has been covered on the Jimmy Medcalf Technical days over the last 25 years so it quite widely used.

My kindest regards and very best wishes for the New Year.
Jimmy (J D Medcalf, BDC President)


Ed Gehringer - Dec 28, 2013
Hi Robert, I had an early 3L (1924 - Chassis 528), on which I installed a coil and oil filter on the near side.

Click for larger view

This car never let me down on tours through the Alps, the NAVBM, two Nova Scotia tours, and many on the west coast. It was so easy to change the Fram filter and know that the 50W oil was always clean. I like the mag/coil setup as well; the car started very quickly and always performed well. The only drawback was the small autovac, which on very long, gradual grades would sometimes run dry, requiring a stop on the shoulder to allow it to recover.

Happy 2014 Robert.


Gregory Porter - Dec 27, 2013
Dear Robert, my dad John Porter was the guy who started fitting pre lube system to Bentleys. It was a good system and eliminated the risk of dry starting a motor. The outfit that made the pre lube pumps went out of business.

When it comes to oil filters my thoughts are very in favor. Modern engine oil is not designed for white metal engines, and any protection that can be added is a good idea. The modern oil filter kits sold by the club are simple, and they also do not effect a cars originality. They in fact make the car more useable.

Sincerely, Greg Porter


Donald Day - Dec 27, 2013
Dear Robert, Thank you for your interesting email.

Regarding oil filtration: If the engine has been converted to run on modern shell bearings, oil filtration of some form should be introduced: if it is still running on white metal, it is not necessary to modify anything. The best improvement to a 3-litre's oil system is to double the speed of the pump - for which we can supply the appropriate crankshaft and oil pump shaft gears.

My own 3-litre has no oil filtration, a double speed pump which gives about 60 psi continuously, has shell bearings for its much stronger modern connecting rods and modern case hardened crankshaft but still has white metal mains and has run satisfactorily for the past 18 years.

I do hope this helps.
With best wishes for the New Year,
Donald Day


David Morley - Dec 27, 2013
I made this modification six years ago and it has worked extremely well since. (I added it to the BDCL forum at the time.) The original filter is just a gauze which only removes the big bits! Since fitting the filter, sludging in the sump is cured and the oil stays cleaner longer. Oil pressure is unaffected and it has the advantage of fitting within the original casing so does not detract from the vintage look. If required there is a version of the filter with a bypass valve, though regular oil changes should remove the requirement for this.

Click for larger view

The pipework and internal parts of the filter

A cross sectional drawing of the filter

The locating discs showing the seal in the bottom one

The filter is a Mahle OX17 there are several equivalents but I've been told that the FRAM parts are not as good in construction or filtration. This filter is about 1" longer than the recommended Land Rover part. In my case the filter casing was orientated so that the flow was from outer to inner, I don't know if this is normal, but it's a simple matter to rotate it until the pipes fit this way around. All I had to make were two locating discs, the bottom one of which I machined to take a rubber seal, but a bead of RTV allowed to cure first is just as good, this located around the lip on the bottom end casing which centralised the original gauze filter. The materials were chosen by their availability from the scrap box! I took the opportunity to clean out the sump at the same time and found about a quarter inch of sludge in the bottom. It may be that I have a good oil pump but the pressure comes up about 10 secs after starting and goes straight to 40lbs/sqinch as it always did. once the engine is hot it falls to about 25 on tickover. This is just the same as it was before fitting the filter.

Thanks for the magazine and a Very Merry Bentlying!

Oil filter and circulation system in Vintage Bentleys
By Robert McLellan

Should the oil filter and circulation system on an early 3 Litre (or any other Vintage Bentley) be maintained as original or can it, or should it be improved or replaced? There have been several attempts in the past and apparently with good results. One disadvantage is that originality is altered. In some cases, drastically. There have been several replacement filter systems suggested in the past. Going a step further are the modifications that were done to The Great American Racer, an early 3 Litre owned by Dick Burdick that has made several rally runs across the United States. The objective was to limit engine wear and increase reliability with a modern oil pump/filter system on chassis 392. View photos of this system on his chassis page. When the engine is started, the pressure is instantly high and remains high at idle and under acceleration and deceleration. It is not just a modern oil filter. His mechanic said a modern oil filter alone would not work because it would restrict flow efficiency. A modern oil filter needs a pressurized system.

Vintage Bentley owner and restorer Alan Smith made these comments, which readers will find of interest:

"A few years ago some American Bentley owners such as Bill Porter fitted pre pressure oil systems to their engines. These systems used an external oil pressure source that would pressurize the oil system prior to starting up the engine, the theory being that this would minimize engine wear as the engine normally rotates several times before the oil pressure pump is able to bring the system up to pressure.

Looking at the photos of Dick Burdick's car I can see that the oil filter system is the same as on my engine in that he has fitted a full flow oil filter but there is something else that I can't identify but I suspect that it is an external pressure device.

The modern full flow oil filter that I fitted to my car is the same system as on a modern car but on a modern car the filter is fitted to the side of the crankcase to an internal oilway.

I don't know anyone that has fitted this external oil pressure system, the only way to know if this system does work is to do comparison tests on an engine that is fitted with the system and on an engine that is not fitted with this system. I suppose it's just too much work so we will never know!

Perhaps you can ask the mechanic if such tests were carried out but I bet that they weren't, so this theory is really unproven.

The filter system that you have (on your car) at the moment is fine, is full flow but liable to failure if water is in the oil. The solution is to fit a full flow external oil filter which has a bypass fitted such as the one on my car, making sure that the filter is mounted in the correct direction relative to the oil flow (direction arrows on the filter nozzles will show this).

As regards wear on start up, a good synthetic multi grade oil will help but as nowadays the cars are just languishing in the garages and never taken out — this problem with wear is really just academic."

My response was that my discussion with Dick Burdick's mechanic/restorer was about 20 years ago and the Burdick museum was closed and the cars sold. I would think the subject of filters and oil pumps is worthy of discussion. After all, we do not want our engines to wear out and technology has changed. Is there a better way or was W.O. Bentley's way adequate? What are your solutions? Do you have a revised system? Is there one being produced to our cars?

Updated on Feb 12, 2013
Posted on Jan 08, 2013
Jan 18, 2017 - Info and photographs added for Registration No. GP 42
Jan 17, 2017 - Info and photograph added for Registration No. UV 3070
Jan 15, 2017 - Information received from Adrian Cole for Registration No. HR 9538

October 2017 issue
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