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MG Midget and Sprite Technical - Timing Case Breather

I've searched the archive without success in reinstating an earlier thread about my breather set up. Some of you will remember that the PO had changed the breather to the rocker cover. After searching for months for a replacement timing chain cover for my 1275, I've decided to modify the cover I have, by drilling a hole in it and welding a take off to it. The problem I then have is that I have no oil separator cannister. So the question is, can I use something else like a Mini clutch case breather or would the oil catch tank made from a coffee canister that I have installed be enough? Unless someone has a timing case lurking in the back of their garage.


Pete Ottewell

I remember that well Pete. Yup, as long as the separated oil can drain back to the cover, the clutch breather from a mini will work well. Otherwise you'll be emptying it a lot I reckon.

I was fortunate enough to purchase the BMC prototype timing cover/breather from Dave O, on here if you recall, so that I can experiment with my breather system. I'll get around to that, sometime this year hopefully.

Lawrence Slater

Think this was your thread Pete.

Breather Pipe 1275 12 March 2012

Can't seem to post a link that works for the archive. I forget why and how to do it.
Lawrence Slater

Yes Lawrence found it thanks. It was Guy's idea for the oil catch tank made from an Illy coffee can, it works really well. However, I'm still using a lot of oil and I suspect the crank case fumes are not effectively breathing through the rocker and I'm getting blow by due to the crankcase pressure. The fumes are probably battling against the amount of oil draining back from the rockers.
Pete Ottewell

Pete,

If you are interested, I have what I am told is a Mini timing cover with breather canister. It won't fit the midget, but you could butcher it and install the canister remotely.

Jonathan
Jonathan Severn

I thought the Mini 1275 ones would fit using a different gasket? If not why not, does anyone know for sure?
David Smith

Pete,
is your oil filler cap the vented/filtered type or sealed type?
Nigel Atkins

Nigel, the filer cap is the sealed type.

Jonathan, I may be interested if I cannot get the original, can you e-mail me ppeteo at sky dot com with price details etc.

Thanks
Pete Ottewell

can I suggest you try a vented/filtered cap then £3.95 from MGOC Spares - if you lived nearby you could have one of my NOS just for your good looks
Nigel Atkins

Nigel, what benifit would that give?
Pete Ottewell

The Illy catch tank system seems to work well, but I think the crucial bit that is missing in your particular set-up, Pete, is the canister component. So you will be getting more oil through into the catch tank than is ideal.

I think that the canister fitted on the chaincase is positioned specifically in the air flow from the rad so as to keep it (relatively) cool, allowing hot oil vapour to condense onto the "brillo pad" inside the canister and then drain by gravity back into the chaincase. This should in effect cleanse much of the oil going on towards the carbs. The Illy catch tank is just a sort of second line defence, but of course has no facility for draining back into the engine.
Guy W

Guy, at the start of the thread I explained that I want to install the missing canister but I have been unable to source a timing chain cover. I'm now looking at alternatives like modifying the case I have and welding on an alternative like a Mini breather canister. The Illy can works well but as you say this needs to be emptied periodically which is a messy job. I'm more concerned about crank case pressure and blow by.
Pete Ottewell

Hi Pete, yes I realised that you had hoped to source a canister-type chaincover. I was only adding my thoughts because I am not sure that others necessarily realise why the canister is designed like that. i.e as a cooling system for the oil.

My Illy tank is very slow to fill. I can more or less forget about it. If yours is filling faster then it perhaps reinforces the point about the effectiveness of the canister as a first line oil separator system. So if you can replicate it in some way that must be the right way to go.
Guy W

Guy I'm wondering if I modify/replace the Illy can with a new one that drains from the bottom and move it to the front of the engine bay but feed from the chain case that that would do the job. It would effectively repace the original canister. I could solder a brass tailpiece to the chain case. Take a pice of breather pipe to a tail pipe in the bottom of the Illy can and another from the top to the carbs.
Pete Ottewell

Certainly worth a try.

I also wonder if there is an effect on the temperature of the oil vapour coming through a relatively narrow opening, and then suddenly expanding into the larger diameter of the canister. In theory this sudden expansion should cause a drop in temperature and maybe initiate precipitation of oil droplets onto the wire wool filler.

If this is a real effect, then your Illy can should have much the same result.
Guy W

Timing covers:
'I thought the Mini 1275 ones would fit using a different gasket? If not why not, does anyone know for sure?'

anyone?
David Smith

Pete,
the vented and filtered cap has a hole in it - unless I'm missing something you have a closed system which would be causing -
>>and I suspect the crank case fumes are not effectively breathing through the rocker and I'm getting blow by due to the crankcase pressure.<<

I might be wrong but my engine has a 'breather hole' and I'm told it's better to use the plastic vented/filtered than the smart chrome oil filler caps as the plastic ones 'breath' better
Nigel Atkins

Nigel,

The system is designed to draw air IN through the oil filler breather hole, DOWN through the block and crankcase, through to the timing case and cover, UP via the canister on the timing cover, and into the mainfold. If you block or remove the hole in the oil filler cap, you'll reduce the systems efficiency.

I've always thought that Petes system can't work properly, and clearly it doesn't, which is why he's looking for the the timing cover with the breather.

If you introduce a breather hole into petes system as it is, via the filler cap, all you'll achieve is to draw air into the rocker cover, and straight back out again into the manifold.

Once the timing cover breather is in place, I think the rocker cover coffee can should be removed, as otherwise the system will be fighting against itself.

Lawrence Slater

yes I think the same Lawrence I just thought it might ease the pressure and lead Pete in the (hopefully) right direction

I was going to suggest once the car was run up to temp with the car running that Pete takes the existing oil filler cap of and see what he hears

sometimes things have to be taken in stages rather than going straight to the end and as Pete hasn't got the timing cover yet this could be one of those times
Nigel Atkins

As an alternative you might consider plumbing the rocker cover and timing case into a vented catch tank. You'll lose the closed circuit breather element as the crankcase is open to atmosphere, but using this I don't collect or lose any significant amounts of oil, and the engine isn't ingesting it either.


F Pollock

Pete's got the later breather to carbs arrrangement (but minus the timing cover cannister at the moment) same as mine - mine (with plastic vented/filtered oil filler cap) works fine with no oil consmpsion from it so the standard system is good too
Nigel Atkins

What we seem to be saying here is that if you want correct engine breathing just revert to the original set up (if you can get the parts). Otherwise you'll end up wasteing valuable time botching it up and then going round in circles debateing why it doesn't work.

S G Macfarlane

Actually I wonder if BMC ever got it absolutely right on our versions of the A series engines. Even with the original set-up you can still get a bit of excess sump pressure, and thereby oil pushed out the rear scroll.

Not too mention the possibility of oil being sucked up the breather pipe in quantity.

Shush!!!!!!!!!!!!! I said not to mention that. :)

Anyway, maybe Fergus has it right. Guy has similar, if I remember his description correctly from the other threads?
Lawrence Slater

Mine was the standard 1275 system, i.e. air in via vented oil filler cap Out through chaincase cover fitted with canister and thence via the Y branch to the carbs.

BMC had tried various other breather set-ups which were appropriate to the lower displacement/ lower output engines, and the 1275 version was the culmination of their development of the breather arrangements for this engine in standard tune. Doesn't mean it cannot be improved on. Or more specifically that it doesn't need to be improved on if you are running a modified engine.

In my case I don't any longer have the Y piece (because I use a single HIF carb!) And I have added a second line defence of an oil catch tank, but this is still part of the active "negative pressure" designed crankcase evacuation system.
Guy W

Ah yes, I remember now Guy.
Lawrence Slater

'I thought the Mini 1275 ones would fit using a different gasket? If not why not, does anyone know for sure?'


Early Mini 1275 will fit using same gasket.

Later version with tensioner 'bulge' can be made to fit.
Dave O'Neill2

thanks Dave, thought so - a simple solution for Pete then.
David Smith

Jonathan, you have mail....
Pete Ottewell

Jonatan has let me have his spare mini timing cover. So i'm going to chop the canister of and attach it to the timing cover I have. I will post the results. I've tried everywhere I can think of to get the pucker part without success. There must be one outhere somewhere but hey if this works it will be a problem forgoten.
Pete Ottewell

Pete why not just fit the Mini one?
David Smith

I think it's a different shape.
Pete Ottewell

Pete
If you don't know the history of the cannister it would be a good idea to get it soaked in a reconditioner's cleaning tank overnight as the excessive fumes from a very tired engine can clag up the gauze and reduce the cannister's efficiency.
Paul Walbran

Pete have you not been following this thread you started? Early ones are a straight fit and late ones can be made to fit, need a different gasket.
David Smith

David, yes I have been following the thread, but I'm not sure how the cover can fit even with a different gasket. I'll wait until I have the cover from Jonathan and see if I can get it to fit. But with the tentioner bridge it may look a bit odd. We'll see, I'll keep you posted.
Pete Ottewell

I've not done it myself but seen them fitted on race Midgets; Dave O might know the details.
David Smith

Update on the timing chain cover. I managed to get a MOWOG cover with a breather from Evil Bay. Fitted it today.
Pete Ottewell

IF it's got the front oil separator/cannister/thingy/whatsit attached to the front of it and IF you're going to connect up the carb y-pipe to it instead of your present can then you can -

a) remove fitted additional can and the other hose pipe to rocker cover and put a filter on the metal rocker cover attachment pipe

b) remove can and other hose pipe to rocker cover and block off the metal rocker cover attachment pipe and fit a vented/filtered oil filler cap so that it's the same as standard
Nigel Atkins

Yes, Nigel , that's pretty much what I intend to do today. However, I've replaced the rocker cover and am using a vented filler cap. You were up late last night, was the nurse late.
Pete Ottewell

Nigel: you forgot:

c) open up new thread "oil sucked up from timing cover breather into intake manifold"
G Williams (Graeme)

Pete'll be OK cos he's copying the way the factory did it and it seems to work :)

Pete,
to answer your question - no wet bed !
Nigel Atkins

Nigel: so did I, but it didn't work (but mine use the pancake psv unit).
Where's Lawrence? Still reading Front Wheel Bearings?
G Williams (Graeme)

No not reading/posting on wheel bearings, until JL answers David's question about supplying the shim pack and also maybe the 1mm - 2mm shim in case 2mm bearings can't be obtained.

And until the next reply comes in from Firstline.

Does this count as thread leak, drift, or crossover?

btw. Congrat's on the new timing cover with breather Pete. Just to be on topic at least somewhere in this post :)
Lawrence Slater

Not sure if this will help.

The later Metro timing cover with the bulge will fit early Midget crankcases/front plates without any mod but the later 1275-ish front plates with the reinforcing channel under the dynamo pulley adjuster will need a little of the reinforcer cut back. Also, inside the cover there is a small ring of metal that MAY foul the duplex timing gears, if fitted. I used a Metro cover, an 'adjusted' 1275 front plate, duplex gears and the Metro tensioner assembly on all of the engines I built over a 10 year period.

Has anyone thought about putting the hole for the small 'canister' through the rear of the front plate? It would then be just forwards of the fuel pump hole and in a good place to meet up with any other vents. Just a thought.
r thomas

This thread was discussed between 04/08/2012 and 31/03/2013

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