17 replies to this topic

[1976 clubamn]

does anyone have a diagram of the breather system? i am having trouble finding what all the pipe work is for and where they all go.

i have got all the basics put some of it just isnt clear. as my mini has been in bits for so long now, it is all a little hazy. if anyone acan help that would be great.

cheers

[Guess-Works.com]

there isn't a breather system as such, depends realy where you breathers are on the engine...

998's there's normally just the one on the tappet cover, and sometime on the timing cover, technicaly the oil cap is also a breather. On 1300's there could be one on the flywheel housing, and the timing cover. Essentiall if there is only one, then it is piped directly into the carb, two are usually connected with a "Y" piece and into the carb. You can vent to atmosphere, but put one of those little K&N type filters on the end...

The alternative is to build a bespoke breather system ( including the rocker cover ) and vent to an external collector tank ( ala racing vehicles )

[998dave]

Following from guessworks

Car's all used to vent to atmosphere, but this was outlawed on new cars as it's emissions, However you can modify the vehicle ignoring this regulation and breath to atmosphere.

The normal breather is on the right hand cam-follower cover going up that side of the engine through a filter element, and into the carb inlet.

I'm planning on building a 1275 with two blank cam-follower covers, and instead put a breather pipe and filter to atmosphere of the clutch housing end of the engine to simplify the bay and alloy easier fitment of an Ultimate Head Steady,

Dave

[1976 clubamn]

thanks for the input guys.

im going to build my own system with a catch tank.

[998dave]

You'll forget to empty the catch tank!

Just put a tube upwards above the head gasket level and fit a small filter at the top to breath to atmosphere. Oil residue will cool enough and go back down the pipe, or get caught int he filter. And a small amount may dissapear, but will vent out nicely, rather then collecting and going mingy...

This type of pipe is what u want to make.....



Note pic on ebay, so may dissapear within a week or two.

Dave

[Jammy]

Ok, call me nieve but why do you need breathers?! And why do race cars need a catch tank?!

[Pavel]

I believe race cars require them to stop oil going out and onto the track..

[Jammy]

Thought it might be that! And do engines need breathers to stop pressure building up too much or for cooling or what?

[Pavel]

Basically it's too prevent pressurizing of the engine which would cause all sorts of problems...

[Jammy]

Again, thought it might be something like that, I think i should get round to building my own engine to really understand how everything works! (I do have an old 850 next to my house!!)

[998dave]

Breathers:

Contrary to what everyone gets told the combustion chamber isn't sealed, infact you get what's known as blow-by when combustion gases escape past the piston down the cylinder, into the crank case.
This is 10-20 litres per minute... seems a lot? at 4000rpm your 998 mini will transfer 40000 litres. 20 isn't a lot...
Now this gets in the crankcase and pressurises i, which isn't good, so we have a breather normally into the vacuum of the inlet manifold through a PCV (positive crankcase ventillation) valve (effectively a one way valve).
Now instead of doing that we can breathe to ambient, which is also lower pressure then the crankcase.

Dave

[1976 clubamn]

again some great feedback on this. will go and asess the situation and see what would be best for me.

cheers mates

[Dan]

Dave, most 1275's don't have tappet covers anyway. Only Cooper S 1275 blocks do. The breathing on 1275 blocks is from the timing cover and the clutch housing and you will need to vent the timing cover when you build a 1275, as well as the other end. If you don't the timing chest pressurizes and the crank oil seal will fail very early. I run with both the tappet covers blanked off on my 998 and a breather in the timing cover and clutch housing as 1275's have. Keeps it all nice and oil tight.

PCV valves haven't been in use on Mini's for decades.

The oil filler cap is also part of the breathing system, as that's where the fresh air comes into the engine from. That's why you have to change it as part of the service schedule.

[Guess-Works.com]

If you're not using the mechanical fuel pump, you could also use that as breather, you need to modify a blanking plate with a pipe and bring that up the back of the engine alongside the number 1 exhaust pipe. There's a breather on the 1300 Maestros and Montegos which does not take much mudification to fit...

[Jammy]

What is there in or on the oil filler cap that deteriorates or whatever that makes it part of the service schedule.