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MG Midget and Sprite Technical - by-pass in oil filter

I do not see a by-pass in the Tecalemit and Purolator oil filters. Is this correct?

Flip


Flip Brühl

Definitely one in the purolator.
anamnesis

Anam,
Where can I see it in the image?
Flip
Flip Brühl

Inside. Comes as part of it, not separately. It's a sprung loaded valve, that operates if the filter clogs up.

I might have taken a pic of one, I'll look. Someone might have one off, that they could snap for you.
anamnesis

inside part number 16?
Flip Brühl

Actually I stand corrected. Maybe not all purolators had one.

You can those that did by the blocked filter warning light spade terminal on the top.


anamnesis

Flip. You are correct. Oil filters, either the cannister or the cartridge type, do not have any form of oil bypass mechanism built into them. The oil bypass mechanism, which allows the unfiltered oil to continue to flow to engine bearings if the oil filter becomes blocked, is located on the engine as part of the mechanism that the oil filter is associated with--e.g. the 18V oil filter adapter for the B series engine.

What some oil filters, all of the self contained "cannister" type, have is an anti-drain back valve on oil filters that may be used in applications where the filter is not hanging straight downwards. If the filter is hanging straight downwards, gravity keeps it full of oil when the engine is not running. Invert it, however, (again the B series adapter is a good example) and gravity would drain the oil from the filter causing a brief period of oil starvation at the bearings (perhaps) until the filter had refilled and oil was flowing through it.

So, no commonly encountered oil filter will have a built in by-pass mechanism.

Les
Les Bengtson

Fkip is talking about Spridgets not B's.

Assuming I understand what you are saying Les Bengtson , that's not true for all Spridget oil filter housings. The picture I posted shows the spade terminal for the warning light, that shows when you have a blocked/clogged oil filter. Under those conditions, the oil bypasses the filter through a valve inside the head of the housing. I have this type on my Sptite. It was more common on the early tyoes and the warning light was in the top centre of the dashboard.
anamnesis

This is from the moss website for minors. But Spridgets had them too.

Inside part number 120 Flip.

120. PART NUMBER: 17H9463
APPLICATION: Purolator Filter Type

This is the type that contains the warning light terminal and internal bypass. The bypass is not listed or supplied separately

https://www.moss-europe.co.uk/external-engine-minor-1951-71.html

I've never actually worked out exactly how it works. But I assume if the filter clogs, the sprung plate under the paper filter element lifts, allowing unfiltered oil to operate the warning light switch, and enter the engine.



anamnesis

Part number 87 on this moss Spridget drawing.


87. HEAD, with filter condition sensor
PART NUMBER: 37H1528

APPLICATION: From (e) 12CC to (e) 12CE/Da/H10308

https://www.moss-europe.co.uk/external-engine-sprite-iv-midget-iii-1500-1958-66.html

Your earlier picture was the early type. So now I see that only mk4 Sprite and mk3 Mudgets had them. Not the earlier marques.





anamnesis

Giving this more thought Flip, there IS a bypass in all of the paper element type oil filter housings. It's just that on the later type that I drew attention to, there is also provision for a warning light.

The bypass is the same. If the filter blocks, the bottom plate (91 in this picture), is blown off against the spring, and unfiltered oil is pumped into the block.

I doubt the filter blocks very often, if at all. Hence some convert to the spin on housing and metal cartridge, that does not have a bypass in the head at all.



anamnesis

From the Fram 'Technical Information' sheet (attached). -

"Relief (By-pass) Valve

In a full oil flow system, all the oil passes through the filter to reach the engine. If the filter clogs, an
alternative route to the engine must be provided for the oil, or the bearings and other internal parts may fail, due to oil starvation.

A relief, or by-pass, valve is used to allow unfiltered oil to lubricate the engine. Unfiltered oil is far better than no oil at all.

This relief valve is built into the engine block in some cars. Otherwise, the relief valve is a component of the oil filter itself. Under normal conditions, the valve remains closed. When there is sufficient contaminant in the oil filter to reach a preset level of restriction to oil flow (around 8 PSI in most passenger cars), pressure on the relief valve causes it to open. This condition can occur when the oil filter has become clogged or when the weather is cold and the oil is thick and flows slowly."

Some screw-on filters for our cars have a 'by-pass' valve built into them, such as K&N and some Fram.

Nigel Atkins

Very interesting this filter condition sensor! I never saw one but I only know something about frog eyes.
The oil in the Tecalemit and Purolator arrives from the outside of the paper element and goes to the centre. So a clogged filter will be pressed HARDER against the top of the filter housing.
Flip Brühl

Not so Flip.

But not *exactly* as I described. As I said, I never worked out exactly how it works, only that it works in some way connected to the sprung pressure plate.

But as you say, the oil enters the filter from the outside, not the inside.

So what happens in the event of a blocked filter, is the entire filter is forced DOWN, against the sprung pressure plate, and OFF the seal in the filter housing. This opens a path for unfiltered oil into the engine, AND, in the later housings, exposes the blocked filter switch to oil pressure, which turns on the light.

This picture isn't of a purolator or a tecalemit paper element, it's a screw on cartridge filter, but it illustrates the same thing.

So you DO have an oil bypass for a blocked filter in Frogs too.

What could be a problem, from what Nigel put, is that only SOME screw on cartridge filters have this. Which makes sense, as some engines are designed with an inbuilt 'blocked filter' oil bypass mechanism, and hence don't need one in the cartridge too.

So if converting to the screw on type oil filter on A series engines, make sure to get one that does have a bypass, such as those Nigel suggested.






anamnesis

Thank you Anam for the picture and being so involved in my problem. I also thought that the spring pressure plate gave room for the by-pass. I am writing an article about oil filters for te Dutch Healey magazine (in Dutch). Than I suddenly realized that I can't understand how and why the element is pressed down bij oil pressure,

Flip
Flip Brühl

Flip,
don't forget also about very cold oil sometimes being too thick to pass through.

See here for more info. - https://www.mobil.com/en/lubricants/for-personal-vehicles/auto-care/all-about-oil/different-types-of-oil-filters-and-how-they-work

"3-D animation of a MAHLE / Knecht oil filter. Explanation of function of the valves and the filter element. Oil flow through the spin-on oil filter. The high quality oil filter insure excellent function of the combustion engine and insure perfect performance and long life time of an engine." - https://www.youtube.com/watch?v=SBYEviKFlXA

Nigel Atkins

That's a very good description Nigel. Who'd have thought that we'd go back to the future with separate filters. I never chnged. I like the old housing.

Interesting point about cold oil being too thick and causing the oil to bypass the filter end enter the engine dirty. Wynns anybody? I used to use that. Made the oil almost like treacle in the winter. I wonder if it caused a bypass situation. But as my engines always lasted to near 100k miles, it didn't matter. But of course oil and even Wynns was cheap back then, so frequent oil changes were the order of the day, meaning mostly 'ckean oil' all the time..

Yep It's more interesting than it seems Flip. Although I knew there was a bypass, until now, I'd never bothered to work out exactly how it worked. Now I know, thanks to your question.

I also hadn't given any thought to how the bypass worked in the spin on cartridge filter. Thanks Nigel.

So for environmental reasons, I wonder if cartridge filters will get harder and more expensive to obtain.

Will all those who converted, now be digging out their old purolator housings, or looking for one on Ebay at an inflated price? 😁. Maybe I have a spare I could sell. 🥴
anamnesis

Modern cars did go back to cartridge filters.
Nigel Atkins

This thread was discussed between 29/08/2021 and 01/09/2021

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