SRM oil pump

[BSA_54A10]

Very Big Snip

But I do like return line filters as they are better than relying on a bit of gauze.
I guess what we really need is a window in the timing cover so we can still look at that rather expensive blue device pumping the engines lifeblood    rather than it being hidden away...

I had expected substantially better knowledge of the BSA filtering system from you.

The gauze in the sump is there to protect the oil pump.
If it can get through the gauze it will pass through the return side of the pump without damage to the pump.

The gauze in the oil tank outlet is there to protect the pressure side of the oil pump.
If it fits through the gauze it will pass through the oil pump without damaging the oil pump.

The gap between the main shaft & main shaft bush is in the order of 0.0001" to 0.0005", so any particle bigger than that can not get into the bush to do any damage and will pass through the hole in the timing bush into the crank.

The same thing happens at the big end.
Only particles bigger than the clearence between the slippers and the journals can pass into the bearing, the remainder will pass into the FULL FLOW CENTRIFUGAL OIL FILTER , commonly incorrectly termed the sludge trap.
here anything that has a heavier specific gravity than the oil will be flung out of the oil and FORM A SLUDGE in the sludge trap.
Or to put it another way, the sludge trap creates a sludge it does not filter sludge out .

The oil then gets pumped back up to the SETTELING TANK where the output on the top allows volatile contaminats ( like water & fuel ) to exit via the breather. Particles with a lighter Specific Gravity than oil will form a scum on the top of the setteling tank and particles with a heavier specific gravity will drop down below the outlet level.
Eventually the lighter particles will agglomerate ( if you are not using a detergent oil ) into heavier lumps and sink to the bottom of the settleing tank.

Thus each and every part of the 4 level filtering system has a specific job and does that job relatively well when the motor is being used within the design parrameters.

Note, a paper filter mearly filter everything out in one hit, by particle size alone . typically 50 to 120 microns.
However unlike the BSA filters, it does restrict the oil flow which is why it is best put in the return line as the gear pump used by BSA in not a particularly high pressure pump and fairly low volume and never designed to be hooked up to a cartridge filter.
If we have a good think, we will remember many people on this list stating that after fitting the spin on filter, their sludge trap was empty so all the external filter is actually doing s replacing the internal one.

No matter what external filter is fitted, you still need the 2 gauzes to protect the oil pump.

[Greybeard]

Fantastically valuable insight, thank you! 

[kiwipom]

hi Trevor, are all multigrade oils (detergent oil), as detergent is the medium that allow water to mix with oil so will allow water(condensation) to get carried around the engine which cant be a good thing, cheers 

[bsa-bill]

The trouble with age (well one of them) is you find yourself starting sentences with " I remember reading somewhere----" which casts some doubt as to the validity of  whatever it was you read so ---  take this with however many pinches of salt you require.
The first Multi-grade in UK was DucKhams Q 20/40 designed for either or both the Mini engine or Triump motorcycle engines.
The Mini one I don't reckon as that engine had been used in many cars prior to sir Alec's little gem.
I used it in Mini's but didn't find it magically made the yellow grunge in the rocker box disappear at all.
Modern oil is designed to work with Catalytic converters, to do this they lack a component of previous oils that destroys the Cats but was of a benefit to your older engine.
Interesting article here http://www.classiccars4sale.net/classic-car-how-to-guides/feature-articles/a-guide-to-classic-oils
So for myself I'd use anything for an older engine.
Duckhams BTW was owned by BP who tried to sell it some time ago - don't know who bought it if anyone did

[BSA_54A10]

hi Trevor, are all multigrade oils (detergent oil), as detergent is the medium that allow water to mix with oil so will allow water(condensation) to get carried around the engine which cant be a good thing, cheers

Detergents, in any liquid, water , oil , whatever are nothing more than a molecule that would rather adhere to anything else other than the liquid it has been mixed into.
I am sure we have had this conversation before.
So in a detergent oil the detergent molecules which typically are less dense than the oil molecules attach themselves to anything that is not oil, or themselves.
This firstly makes the "foreign" molecule bigger so it can easily be filtered out and also stops the foreign molecules joining together and sinking to the bottom where they form a sludge.
This is exactly what you don't want to happen in a system that relies on a heavier specific gravity to centrifuge off the foreign molecules but you do want if you are passing your oil through a paper filter.

in oils DETERGENTS ARE DISPERSANTS, the terms are interchangable.

In the kitchen sink the same thing happens.
The detergents wrap around the dirt on your plates and hold the molecules in suspension which is why the water goes cloudy.
In an oil slick, water based detergents grab the non water molecules, mostly the oil and envelope them breaking up the slick.
The difference here is the detergents are heavier than water so the oil + detergent drops to the bottom of the ocean / river.
The detergents have bacteria on one end that breaks down the oil.
In rivers the detergent is lighter than water so it forms a scum on the top which is easily scooped off

[RichardL]

Trevor,

I am certain I must be misreading and/or misunderstnading something you said in the filtering explanation (useful and interesting, indeed). Here is the statement in question:

The same thing happens at the big end.
Only particles bigger than the clearence between the slippers and the journals can pass into the bearing, the remainder will pass into the FULL FLOW CENTRIFUGAL OIL FILTER , commonly incorrectly termed the sludge trap.

I am reading this as somehow saying that the slipper gap is sorting out the particles for removal by the centrifugal system. Isn't it the case that the trap tunnel fills with oil where heavier particles are spun to the outside while the now-filtered oil goes to the slippers via the journal holes toward the centerline? Three possibilites, in order of likelihood: I'm too thick to understand you; I have misread your post and would get it if only set straight; you slightly mis-wrote what you meant to say.

Thanks for clearing this up with having to point out that I am thick, even if I actually got it right.

Richard L.

[Greybeard]

...The Mini one I don't reckon as that engine had been used in many cars prior to sir Alec's little gem.

True but sharing the oil with the gearbox was a new idea for UK. Maybe Duckhams was good for that combination.

[chaterlea25]

Hi All,

    ...The Mini one I don't reckon as that engine had been used in many cars prior to sir Alec's little gem.

True but sharing the oil with the gearbox was a new idea for UK. Maybe Duckhams was good for that combination.

Thats What I remember being told ?
Duckhams Q20/50  was developed for the combined engine and gearbox

I had a fair few mini's back in the 70's and always ran them on Duckhams
One time the factors pushed me to buy Silkolene 20/50 so I tried a gallon
After about a thousand miles I noticed the hot oil pressure was lower than before
I changed back to Duckhams and all was well again
Some times mini owners would add Wynnes or STP to the oil in a bid to keeep oil pressure up
The additive would coat the needle bearings in the transfer gear, they would then over heat and fail in short order 

John

[bsa-bill]

True but sharing the oil with the gearbox was a new idea for UK. Maybe Duckhams was good for that combination.

 Good point, it did cross my mind when I was typing, also often stated D Q20/40 was for air cooled engines, more theories than you can shake a stick at as they say

[KiwiGF]

Trevor,

I am certain I must be misreading and/or misunderstnading something you said in the filtering explanation (useful and interesting, indeed). Here is the statement in question:



I am reading this as somehow saying that the slipper gap is sorting out the particles for removal by the centrifugal system. Isn't it the case that the trap tunnel fills with oil where heavier particles are spun to the outside while the now-filtered oil goes to the slippers via the journal holes toward the centerline? Three possibilites, in order of likelihood: I'm too thick to understand you; I have misread your post and would get it if only set straight; you slightly mis-wrote what you meant to say.
Richard L.

Hi Richard, this is how I think it works albeit I think some particles too big to pass through the big ends will inevitably reach the big end before being spun out into the sludge trap? Arguably the big end "clearance gap" is then doing the filtering, or at least some of it, when that happens. The oil feed hole in the journal feeding the big ends is positioned so that centripetal force carrries larger particles away from it, so in a perfect world no large particles would ever reach that far down the oil feed path, but I guess when the engine is rotating slowly or is a stopped particles could make it to the oil hole? I also guess larger particles may be knocking around for some time inside the crank before becoming permanent stuck in the trap?

Sort of related I recently read somewhere on this forum the statement that the small journal crank does not have a sludge trap like the large journal, it's a while since I had my SJ crank apart but I do remember cleaning out some small "pockets" in the crank under the oil feed access screws in the crank, which I at the time thought WERE  a sludge trap for particles (they were filled with fairly hard black/grey gunge, anyway).

Maybe someone could confirm or deny the existence of a sludge trap in the SJ crank?

[kiwi george]

As regards to the S/J crank there is no tube in the crank but the space between the two screws acts as a sludge trap.

[Greybeard]

As regards to the S/J crank there is no tube in the crank but the space between the two screws acts as a sludge trap.

My '55 A10 has no tube.

[RichardL]

As regards to the S/J crank there is no tube in the crank but the space between the two screws acts as a sludge trap.

My '55 A10 has no tube.

I take it that is a small journal crank?

[BSA_54A10]

Trevor,

I am certain I must be misreading and/or misunderstnading something you said in the filtering explanation (useful and interesting, indeed). Here is the statement in question:



I am reading this as somehow saying that the slipper gap is sorting out the particles for removal by the centrifugal system. Isn't it the case that the trap tunnel fills with oil where heavier particles are spun to the outside while the now-filtered oil goes to the slippers via the journal holes toward the centerline? Three possibilites, in order of likelihood: I'm too thick to understand you; I have misread your post and would get it if only set straight; you slightly mis-wrote what you meant to say.
Richard L.

Hi Richard, this is how I think it works albeit I think some particles too big to pass through the big ends will inevitably reach the big end before being spun out into the sludge trap? Arguably the big end "clearance gap" is then doing the filtering, or at least some of it, when that happens. The oil feed hole in the journal feeding the big ends is positioned so that centripetal force carrries larger particles away from it, so in a perfect world no large particles would ever reach that far down the oil feed path, but I guess when the engine is rotating slowly or is a stopped particles could make it to the oil hole? I also guess larger particles may be knocking around for some time inside the crank before becoming permanent stuck in the trap?

Sort of related I recently read somewhere on this forum the statement that the small journal crank does not have a sludge trap like the large journal, it's a while since I had my SJ crank apart but I do remember cleaning out some small "pockets" in the crank under the oil feed access screws in the crank, which I at the time thought WERE  a sludge trap for particles (they were filled with fairly hard black/grey gunge, anyway).

Maybe someone could confirm or deny the existence of a sludge trap in the SJ crank?

Have a look a the lubrication diagrams.
The oil passes through the main bearing then into the crank.
The feed hole for the big end is on the inside of the journal and the sludge trap is on the outside.
Drastically heavier particles will be flung into the side of the sludge trap and form a compact sludge.
Lighter particles will flow with the oil but unless they are smaller than the space between the journal and the slippers, they can not get past to do any damage.
That was what I was tying to say if it was not clear.
The space between the journal & the  slippers is finner than paper filter you can fit without overloading the pump.
Most of the filters run from 75 to 200 micron but I can't see BSA owners paying $ 45 for a 75 micron filter.
A sludge trap will pull particles out regardless of their size so stuff as fine as 0.01 micron will be pulled out, just so long as it has a higher specific gravity than the oil and a small co-heasive force between it and the oil.

[peter small]

I run a 1954 Road rocket with a SRM pump and spin off filter.
I use straight sae 40 and dont hang about,
The old pump was original and was U/s and i like filters its not pushing anything bad back into the tank
I fitted a sump plate to allow draining if i lay it up in the winter. but frequent usage it doesn't cause a problem. i do have a anti sumping valve fitted not 100% perfect lets a bit through just like the one in the engine.