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MG Midget and Sprite Technical - Blocked Breather - Have I got one?

I appear to have a blocked breather - canister type on the timing chain cover of a 1275. Blowing back down the tube from the carbs to the breather (oil filler cap off) is very hard work.

I have been advised to change it. Before I do how essential is it to change it/clean it out and how do I know if it is breathing well enough? Are there any other symptoms?

I have had enough user induced maintenance failures over the years to err on the side of caution for non-essential 'repairs', do I need to un-block it?

Mike
Mike Dixon

A subject close to my heart !

You may want to look at the MED Engineering Videos on yout tube as they cover breathers for the A series very thoroughly. It is fair to point out that their applications are perhaps more aimed at the race or modifed engine, but the principle of breathing is nicley covered and worth a look.
To complete my story, I opted for their mechanical fuel take off 'breather' on my mini engine, as the timing chain cover was the closed style, and after i machined a spacer, all i did was connect the pipework to the rocker cover and there we go. This means that the mini now has two breathers into the rocker cover, and the standard one that vents from the clutch cover.
The midget i have vents as yours does, and on my engine there isnt a take off for the fuel pump, whether thats the same for all in line A series, i wouldnt know.
P Bentley

just re read my comment, and it should say. . .
i opted for the breather that uses the take off for the mechanical fuel pump.
P Bentley

Mike,
disconnect the the 1/2" hose from the canister and end of plastic y-piece and then you can straighten it out and look down it for any blockage or partial blockage. Same for two 1/4" pipes to carbs and y-piece.

The 1/2" pipe wants to be thick solid wall type, vacuum hose is often used, not flimsy walled type.

Also there's been a lot of piss-poor rubber about so check the hoses haven't fell apart or shredded themselves internally.

If you have a chrome bling type oil filler cap they don't breather as well as the £3 proper plastic type, you can also check if the plastic type is bunged up (see photo).

If anything is bunged up it'd be best to know what with and why.



Nigel Atkins

Just be aware that although the mini and the Midget both run A series engines, the logic applied to the breather system differs as Minis don't have to deal with the issue (letteraly) of oil and the crankshaft scroll seal.
GuyW

Do you have a link to the MED videos? I have looked on their website, but cannot find them.

Richard
Richard Wale

Mike,
The breather canister itself is unlikely to get so bunged up that you cannot blow through it, though it may still benefit from cleaning. But the most likely explanation from what you have said is that the hose between the canister and the carb Y connector is blocked or has collapsed internally.

Take it off, poke someting through it or thread a string through it and use this to drag a small piece of rag back and forth through it a few times to clean it out. Or just replace with a new length of suitable thick walled hose.
GuyW

The point i was making was that breathing is covered in a useful video, and here it is, i hope :)
https://www.youtube.com/watch?v=U4Flmn9fIhI


P Bentley

Well explained video but that system demonstrated by MED is a passive to atmosphere system. Fine for a mini race engine, but the direct opposite of the active vacuum system used on a 1275 Spridget.
GuyW

On that vid only about the first 30 seconds relates to our systems - and where's the breather at the back?

I think there is/was(?) a University Motors (John Twist) video that showed the breather system but perhaps it was on a MGB, or I might have imagined it, or it's no longer listed(?).

I've seen an explanation somewhere, perhaps on here in the Archives or one of Norm's articles but as Guy and I have put first the pipes want checking for blockage. As we're not told otherwise we assume the system is factory standard for a '71.




Nigel Atkins

My understanding of the breathers on any engine is that they are there to deal with the pressure build up and therefore the aleviate the internal pressure on the seals there in. . .
Are we saying the the original set up cannot be improved upon by additional breathing ? or its not necessary ?
Always happy to learn
The Breather at the back is covered in the dying minute of the video.
P Bentley

Nothing wrong with progress and I'm certainly not knocking you for offering help but I think the basics need dealing with first - if the current system blocked, what with and why.

By Mike's original post he sounds, like me, he's not the best at mechanics and technical matters so the issue is best dealt with one step at a time - well it would with me.

I didn't go much more than the first 30 seconds of that vid as I didn't want to confuse myself or the matter, to me a very non-technical person the vid at that point suggested there was something at the back which I knew wasn't on the factory standard system, unfortunately the camera was pointing elsewhere at the time it was mentioned.

I posted the last photo as an illustration of standard giving the opportunity for Mike to perhaps see or say if his system is different to that for some reason. It also shows an alloy rover cover but with a plastic better vented oil filler cap fitted rather than the usual bling ones.

Nigel Atkins

I completely follow what you are saying Nigel, i didn't take offence or any where near it, so no drama there, we are two guys trying to help the OP. . . .aint he lucky !

So i am clear, if the original system is blocked, then easy peasy issue to resolve as you have pointed out, what i wonder is if a better system is available to run in conjunction with the original, thats all.

Given my recent experience it seems the transverse set up loves more breathing (the hose diamter for the MED kit is something like 15-16mm) so thats what prompted me to think it may help.


P Bentley

PB, there are two radically different types of breather system. The principle idea of that Mini one is to get as much free movement of air out of the crankcase, rocker cover etc as easily and freely as possible. So the system has lots of openings, and generally the larger the better. As an addition he then has an oil catch tank as required for race entry cars.

The Spridget 1275 system aims to achieve the same breathing of the engine, but in a controlled manner so that suction applied (in this case by the carb manifold depression) produces a negative (i.e less than atmospheric) pressure in the engine to prevent oil being forced out of the rear crank 'seal'. This is achieved by having an essentially sealed crankcase with one extraction point and a limited entry via the ventilated oil filler cap. The result is air is drawn through to get rid of crankcase fumes but the restricted entry results in negative crank pressure.

You cannot mix the two principles as additional air entry to the 1275 type will prevent it maintaining that negative pressure in the crankcase and it will then leak oil
GuyW

thanks for the info Guy, i love a bit of learning and your explanation makes sense, thanks for sharing it.
P Bentley

Guy beat me to it, word for word it was what I was going to put ...

yeah right! :)

... actually I was going to direct you to a couple of threads in the Archive. (evil laugh)
Nigel Atkins

Thanks for the input, I do have a bit of a leak from the rear seal but that's fairly common?

I will have a look at the pipe and report back. Here's hoping it could be that simple..

Mike
Mike Dixon

Tube removed - all clear so it's not that. The breather looks very oily, from what little I can see but I would expect that.

I did have another go at blowing through it before I took it off , oil filler cap removed and its possible, but I have no idea how much required pressure is too much. My local mechanic reckoned it was not as free flowing as it should be.

If I leave it on the principle the car seems to be running fine are there any implications? I could not find much in the archives here.

Could be a busy couple of days coming up?

Mike
Interesting video by the way - I note they remove the mesh !)
Mike Dixon

I would leave well alone Mike.
I have never tried blowing into mine but l would expect a fair amount of resistance. You are blowing into a confined space, or series of spaces with no exit other than the oil filler cap. So your puff has to find its way into the crankcase and then up the push rod drainage holes to the rocker cover. Quite a challenge! You could take the dipstick out and try again?
GuyW

Quick thought - I can't remember the exact details but if you have the engine running at idle after fully warmed up and remove the oil filler cap you should notice a (slight?) difference in idling, if so that might be enough reassurance.

ETA: IIRC when I tried blowing down the hose and at the same time holding my hand over the open oil filler tube the air movement I felt on my palm was very slight.


Nigel Atkins

Just tried it with no dipstick - I can feel the the air coming out then I blow so I will take Guy's advice and leave well alone and just change the coolant.

Thanks for all the advice


Mike
Mike Dixon

Mike,
if you're changing your coolant don't forget to remove the engine block drain plug (11/16" IIRC) and rod clean the aperture whilst it's draining, a lot of debris can be there - and follow the refill instructions in the Driver's Handbook for an easy trouble-free refill.



Nigel Atkins

Nigel

Thanks - I think it is a Whitworth one for some reason? Whatever - I have something that fits!

Thanks for the scan

Mike
Mike Dixon

Mike,
that might explain why the spanners I use aren't a great fit, luckily with the copper washer I used the nip to fully tighten, or to loosen, is next to nothings as there's not a lot of space there.
Nigel Atkins

Discovered my 18mm spanner today which reminded me.

Original drain plug was 3/8" Whitworth head (1/4"bsp thread) so I had to buy an 18mm spanner to get a fit.

When I replaced the drain plug the new one seem to fit a 11/16" spanner better.
Nigel Atkins

If you can easily blow back down the breather tube I would be concerned because that means that when the engine is running the suction from the carbs is not effective at preventing rear-end seal leaks because air is flowing so easily through the system.
Graeme Williams

Graeme, Mike said it was quite hard blowing through the vent tube - just as you say it should be. It was slightly easier with the dipstick removed as I had suggested as a test against actual blockage. I would think the system is probably ok.

Incidentally, when measured, the actual suction on the Y piece connection to the carbs with engine running at 3500rpm is barely 2 bar, so pretty slight really. That is with the correct vented oil filler cap and sealing washer on the dipstick tube. If either of these were to leak air in too freely, that suction would drop even lower which is when oil leakage at the rear scroll seal starts being a problem.
GuyW

This thread was discussed between 25/09/2018 and 11/10/2018

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