G'day,
Have now got Minnie running and ready for rego in a couple of weeks. I have a question about how much oil coming from a breather is "normal".

The engine has been fully rebuild. An 850, 40 thou oversize pistons, reco head. It's one of the early 850's that had 2 breathers. One in the main rocker cover and the other is in the push rod covers on the back of the engine under the manifolds. On my engine, this breather faces directly down pointing towards the diff and it an open tube. This is how it was originally and the engine had never been previously out or worked on.

The breather on the rocker cover is clear and hooked into the air cleaner. The breather on the side cover was initially just open to atmosphere. I've done about 200 miles on the motor so far and have been varying speeds / revs etc during the run in. Bit of running up hills etc to help bed rings in. Motor runs fine with no signs of significant back pressure out of rocker cover when I unscrew the oil fill cap. I also can't feel any air coming out of the breather on the side cover although I can't test for long as the exhaust gets a bit warm.

What I've noticed is a fairly significant oil leak on the back of the engine and I've traced this down to oil coming out of the side cover breather. I connected a bit of 5/8" heater hose to the breather outlet and isolated where the oil is coming from. On this 1st test, I used some clear tube in the lower part of the hose so I could see if there was any oil in the hose. I drove it for about 15km and took it up to around 90kph at times. On checking, there was some oil and the clear tube was kinking so I disconnected the hoses in case it blocked and drove back home with the breather open. Only did around 50 - 60 kph to try and limit the amount of oil coming out. Still quite a covering on the diff when I got home so it appears as though the oil is coming out regardless of high revs.

I've since made up a very basic 'çatch can' which consists of a piece of 5/8" hose connected to the breather then going to a Y junction with the downwards arm of the Y having a 8" piece of hose on it and a tap on the end and the other branch of the Y connected to the air filter. I hooked it up like this as if I just connected the hose directly from the breather to the air filter, it has a large downward bend in it and I thought the oil would build up in the bend and possibly block the breather.

I went for another run of about 40km to test the system and no oil leaks anywhere. I've now drained the hose and got about 35ml of oil which is quite a lot I reckon for only a short drive. This amount of oil pretty much filled up the 'drain' hose so any drives much longer would see the oil build up in the rest of the hose.

I know later models had the breather pointing upwards on a 45 degree angle and some also had a metal cannister on them with an outlet to connect to the air filter. With these breathers, the oil would be able to drain back into the motor once you stop. I will fit one of these breathers once I get hold of one.

I have a few questions please:

1/. Why am I getting so much oil out the breather? Given Minnie was on the road for 26 years with an open breather, I'm guessing the old motor didn't push out as much oil as I'm getting now.

2/. Given I can't feel much back pressure from the rocker cover, why is the oil coming out the breather? Is it because the oil can't drain back into the sump quick enough and therefore getting splashed out?

3/. Do you reckon one of the later breathers with the large cannister will do the trick for a long term solution?

Thanks Rocky

that's too much... they did go to the cannister type breather for a reason - I think it would be a smart addition

the rocker cover isn't filling up with oil is it? if so the front cam bearing is upside down - but I reckon it'd be throwing out a lot more oil than you're getting

_________________
did I tell you that I won a trophy?

Thanks Simon. I have checked the rocker cover for oil as I've read about that issue on here but it's fine. I gave it a fairly quick run and checked and also checked while stationary after a few mins at around 3,000 rpm and it's actually hard to see much oil in the rocker cover.

One thing that I've wondered about is the size of the hole in the metal air filter unit I have where the rocker cover breather connects into. I've got an 1 1/2 SU and got hold of a metal air filter housing instead of the plastic ones. On the plastic one, the bit where you connect the breather hose to is about 1/2" diameter and the hole is nearly that ID. With the metal housing, the hole in the connecting bit was only around 1/8" but I've drilled it out a bit more to around 1/4". I was thinking it wouldn't hurt if I drilled it right out to give maximum flow from the rocker cover. Not sure why they made it with such a small hole in it.

Cheers, Rocky

There was a discussion about 850 crankcase venting on Mk1-forum in the UK, if you have access:

http://mk1-forum.net/viewtopic.php?f=3& ... er#p227712

Basically same issue you are having.
Early A series motors just vented to atmosphere through rocker cover and tappet chest. In Morris Minors the oil went down the side of the block onto the road; in minis it ended up over the rear of the power unit!
Mini Cooper tappet chest vents had a rubber tube and metal pipe as standard to stop from dribbling over the gearbox. It attached to that weird, lonely stud sticking out of the tapped hole where later minis had the fuel pump mounted.
I've never owned an 850 but suspect your issues might resolve with the motor bedding in.

Later minis (De Luxe and K) had the rocker cover vent to the air cleaner like the 850, but they had a small oil trap built into the rocker cover to condense the oil before going to the air cleaner so that less oil passed through.

I suspect I might have the same engine as you, Rocky;

Except that mine hasn't been rebuilt. That I know of.
The rear breather behind the exhaust manifold is dry on my engine. The inside of that cover obviously gets oil splashing onto it, but not 'flooded' enough that it comes out the tube.

It might not be a permanent solution, but could you run with that cover upside down, so the tube is pointing at the carby?

Thanks Bill. The old Holdens had much the same thing as the Morris Minors with the breather from the rocker cover going down a pipe that ran down the side of the block to about sump level.
At least they didn't dribble it over the diff housing like mine does.
So you think it might take up a bit once the motor has done a few miles? Hopefully that's the case.

Here's a pic of the sort of cover I'm looking to find and put on. If I had known I'd have oil issues, it would have been easier to fit this before I put the motor in. The extractors look like they'll be in the way a bit. Nothing like a little challenge and standing on my head while I take some bark off my hands while I tackle it.

The Flying Squirrel

That's exactly the same setup as mine Soldar.
I've got a set of C-STR816 extractors on mine instead of the original manifolds that you have and if I turned the cover upside down, the breather tube would foul on the extractors I think. By the looks of it, with the original manifolds I could turn it upside down.
As far as I can tell, the cover with the large cannister on it should fit in ok as the cannister is set off from the cover itself and is on a bit of an angle.

If all else fails, I might have to grab one of the blank covers and make up something to suit.

Either that or run a long length of hose under the car and hook it onto the back bumper and let it dribble out as I go along

That oil trap is used on S models which also use the positive crankcase valve on the inlet manifold (available but expensive new or used) to draw crankcase gases into the inlet fuel mix under vacuum. It also uses a filtered oil filler cap.

I would have thought that you should get away with: a) what you have now; or (b) a mini K type set up with a rocker cover incorporating an oil trap and connected to the air cleaner. Both with non-vented oil filler cap.

Thanks Bill.
So do you reckon the Cooper S type one wouldn't be suitable? A bloke I know who used to be into minis is hunting around in his shed looking for one. Thinks he might have one but not sure.

I haven't seen what the mini K setup looks like. I'll hunt around online and see what I can find. Easier if I can see what I'm after.

Here's a pic of my motor before I had everything bolted up on it so you can see what setup I've got.

Hey Bill,

Is this it? The rocker cover has a large cannister bit on top.

Yes. That is mini K but mine was an early model and the oil trap looked the same but faced towards the radiator - but basically the same concept. They both had a hose going to the air filter canister.
I just thought it might be easier to find a cheap rocker cover with an oil trap (regardless which way it faced) rather than the cooper style side plate with oil trap, which I think is fairly rare/desirable = expensive.

My basic point is that an 850 motor should require about the same crankcase venting that a mini K motor would need: a rocker cover with inbuilt oil trap venting to the air cleaner cannister and a sealed oil filler cap. This setup avoids outlet spouts dribbling oil down the power unit onto the gearbox.
While the compression and oil control rings are bedding in, they probably allow some extra gases to pass into the sump so the crankcase pressure will be slightly higher for a period.

That looks like a heavy duty tow bar on the ride on. Maybe used to tow the Mini around.

Thanks for the help Bill. I'll see what I can hunt down. I didn't know the side cover one I was thinking of was off a Cooper.

Good to hear also that things may settle down after I've done some miles. I was thinking that maybe something was wrong if I was getting higher crankcase pressures. Sounds fairly normal though so that's good.

Nah mate - she's got a turbo fitted and I use it to tow the van

Made it up originally to hook the garden cart on to tow the grandkids around the yard on. Then one day I needed to shift a 6 x 4 and the cook was out in the car so whacked the towball onto it.

Mind you, if Minnie keeps wetting her pants and making the oily mess, I might just tow her around. That'll solve the problem.

Modern materials in rings, bearings, etc don't need any special running-in. Just drive 'normally' without excess high speeds or low speed slogging.