Have always wondered why some minis have a breather plate on the back of the motr, some have a blank plate, and some have a breather that has been corimped. Just wondering what is best and why as I am rebuilding soon.
Thankyou

Good for letting the engine breath, the more the better it stop oil pushing out through your seals. Any type will do.

If by 'crimped' you mean some oil seperator cans have two rings around them, then that was the english made types I think but am not sure.


the more common ones don't have these rings around them. Some don't have the can at all, just the outlet from the cover.

Any will do, maybe consider pulling all the old steel wool out and re-stuffing it with stainless steel wool.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Thankyou.
So why do some just have a blank plate? Is that a design floor?

Some engines don't have these plates at all (I believe the 1275s didn't have them?). On mine one is a blank plate the other has a breather, but not the 'can' type. It is just the pipe which has been crimped at the end.

There is a couple of different systems fitted to our minis....
1) The "crimped" pipe type of side cover it supposed to be used with the "humped" rocker cover. The hump on the rocker cover has the oil seperator in it and it has a hose to the carby. The crimped end on the side cover is actually a very small slot which lets a small amount of air into the engine. This system has a sealed oil cap.

2) This system has the big can on the side cover (or on the clutch housing on 1275 engines) the big can is the oil separator. This system uses a PCV valve (smiths valve) and a vented oil cap.

The idea with both systems is to suck the bad stuff out of the engine without sucking the oil out and without sucking the gaskets in! THey let fresh air into the engine (either by the oil cap or the slot in the crimped pipe) and they both suck to the inlet of the engine.

Anyone got a photo of the crimped type? I'm a little confused..

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

What about the ones which just ahve a blank pipe, with nothing coming out

Was wondering about this recently, mine has the humped rocker cover with a hose running to the carby, this hose has a T piece with a hose joining from the breather on the side plate thingamy. Was this way when I bought it.

all piston engines must have some form of crank case breathing system, if you can imagine the pistons going up & down in their respective bores & with that , on their way on the "down" stroke they suck in all the air fuel mixture & then on the "up" stroke they squeeze all that up & compress it till the spark makes it all go "BANG" & pushes the piston back down again (basic principal but you get the idea) then just imagine all the air "UNDER" the piston getting shoved around too. yeah???

Now there`s very little time for all that air to actually move quick enough to even out, like 2 pistons on their way up & the other 2 on their way down well,,,you`d think that it would all even out right???,,,NOT!!! air has a specific mass & as such tends to take it`s good old lazy time to actually do what it`s being told by the pistons, therefore some "CrankCase" pressure is prevelant,,,ADD to that the fact that the piston rings don`t actually totally "SEAL" so there`s quite a bit of "Piston Ring Blow By" whish is compressed air fuel mixture seeping past the rings & into the lower area under the pistons which is then added to all that other "disurbed" air.

small bore A series engines have a small amount of all that crank case pressure, & the larger 1275s & bigger donks tend to creat very much more, so hence the bigger the A series engine, the more need for more & bigger crank case breathers

to me,,,the more the merrier & the bigger the better, just ask any woman

our big motha race donks have a whole series of huge motha breathers going to a big oil catch tank

the roady versions i build i allways recomend at least 3 breathers if they`re just atmospheric or at least 2 if they`re being sucked into the donk via PCV system or using the later type carb with breather attachment.

preferably the PCV system for road use,,,but if it`s all out power you want then best not to suck all that oil fume into the inlet system dilluting & dirtying up the fuel octane.

clean, cold beautiful wonderful air is best for power, not hot , gundgey oily fumes

But the Dept of transport have their own ideas about air pollution tho & don`t really like seeing engine breathers open to the atmosphere & hence why all the later model cars have wild designed anti polution systems & cat converters & such.

easy-peasy

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

So if I put a breather on the back, that is a good thing? Should I leave it open to the air or attach a hose from it to somewhere else

Forgot to say my motor will be a slightly worked 1100.

More breathing is better. You can just have the breather on the plate with a little pod type KN breather thingy. You can have another one on the flywheel and one on the rocker.

Best thing that we've found is to run a negative crank case breathing system by hooking the breather to a PCV and plumbing it back into the intake manifold. Mind you this is for a side draft carb setup. When I had a SU i just ran it into a oil bottle or KN breather.

Negative crank case makes it idle nice too...

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Lillee - 1969 Morris Mini K

And the A+ spec timing cover with a breather. My LS had one of these, too.

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Cheap, Fast, Reliable. Choose two.

Yep Stu, the LS had that one, but good luck fitting it into a roundnose. Not much room.....
Whatever type you have, do check they are not blocked. My boss's 1275LS had both the flywheel housing and timing cover ones, and both were so full of crud I binned the mesh inside and fitted a woven S/S pot scourer in there. They are just the right size...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Oh yeah. Also you can mod the mechanical fuel pump blanking plate to accept one as well but the Doc says this is no good

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Lillee - 1969 Morris Mini K