Morris Minor Owners Club

The air filter has always tended to become very oily (drips out the bottom) when the breather hose from the rocker cover is connected to the air filter casing.
A few years ago I fitted new rings/big ends and a replaced a couple of sloppy valve guides and expected oiliness this to stop. I was disappointed! So I ran the hose down to the road and the air filter was of course now clean.
Since I fitted 8 new valve guides I reconnected the rocker cover hose to the air filter - it is very oily again and a pool has gathered on the engine bay floor. Very good at stopping rust but very messy. Over 250 miles the oil level has dropped from max to 2 mm above min. Oil was just changed.
I am sure that this loss is all from the breather.
Compression is 11.5 bar - I think roughly 160 psi.
I cleaned the crankcase breather too. I doubt if it is the oil filler cap even 'though I haven't changed it for several oil changes.
This cannot be normal! Any ideas ?
Looking at the size of this post I haven't been very succinct have I !

Do you have a normal rocker cover?
Inside it, there should be a baffle to stop oil splashes getting to the breather hose.Other than that, with new rings and a rebuilt head I'm not sure what else could cause excessive oil to come out of the breather.

If you take the filler cap off during engine running, do you get a big blow out of air? On heavily worn engines (bad rings) you can get gases blowing out of the filler cap almost like the exhaust flow!

If that's not it, you could consider making a bigger baffle in the rocker cover with some aluminium sheet riveted to the old baffle, but that would only be tackling the symptom, not the cause.

When you changed the oil, did you prefill the filter? A dry filter housing can account for something like half a pint of oil, (though you seem to have lost more than that).

One ,RARE,condition you can check for is that the air filter
is the correct Minor one. An identical looking type was fitted
to other,unknown, cars. The difference is in the size of
the hole in the metal tube on to which the rubber pipe from the
rocker cover fits. This hole is about 1/8" diameter only
on the the Minor. The one I had aquired was about 3/8"
diameter and sucked oil into the filter in large quantities!!
Worth a quick look?

Ray : It is a normal rocker cover. No big vent of gas when opened during running - although will check again! Didn't prefill the filter, but always run it for a while and recheck oil level and refill to allow for filter capacity.
Willie : I did replace the filter housing because the original housing was badly damaged and had been even more badly repaired! A 1/2" length of garden hose fits the spigots on the rocker cover and housing - I think that the ID of the rocker spigot and the housing is about 3/8". I will check today and let you know.
This has been bugging me for several years - and after all this time I can't remember whether oily filter started after the housing change. If the hole is > 1/8" I can sleeve it down.
What I did do on Sunday was to drill a 1/8" hole in the oil filler cap (I remember that my old Minis always had a vent hole in the cap) as there wasn't one - the theory being that this would relieve pressure. I then spent the afternoon driving around and didn't have a large pool of oil - a drop or so was forming on the housing. But that wasn't a good test!
Thanks for the response - I will be back!

yes, the rocker pipe is approx 3/8" bore,that is standard,
the filter inlet is definitely not! (I sleeved my over large
one down too and it is still on the car with no problems.
I wonder what year your car is?? does it have the breather
pipe on the tappet cover. Does it have a SOLID oil filler
cap or one with a wire mesh in it?? Does it have a mushroom
like contraption on the inlet manifold??

Willie: the car is a 1964 2dr, 1098 (may be a gold seal engine????)..
It does have the breather pipe on the tappet cover. The oil filler
cap has been changed in previous services. All including the he current one have had a wire mesh in - the top of the curret one was not pierced but I have pierced it (I remember on my 69 and 85 Minis that the cap was pierecd).
Manifold has been changed and has no "mushroom" on top nor did the previous one.
I wonder .... Minis/1100s had a similar air cleaner. Did older Mini's have this air cleaner type (cut off conical paper element) with the large (3/8") bore spigot on the housing and a vented oil filler cap? and did Minors have a non vented oil filler cap with the smaller (1/8") bore spigot on the housing? The point of the vent in the Mini cap being to reduce suction effect?
So far, no oil dripping from the air cleaner .... will be a couple of longer drives before I expect evidence but I am pretty confident of it being fixed!

Well, if you have a tappet chest breather pipe and your
rocker cover pipe feeds in to the AIR FILTER(NOT straight
into the CARB) then you should NOT have an oil filler cap
with wire mesh in it! it should be the solid type! This makes
it even more important that you only have the 1/8" hole in
the air filter inlet pipe. Since you have the wrong filler cap
I can only surmise that you have too large a bore in the
air filter inlet.

I would add that drilling a hole in the wire mesh type of
oil filler cap is a pointless exercise as that is why the
mesh is there....to let air IN. On this type of breather
system the OUTLET is via a pipe to the CARB.
On your type the INLET is the tappet chest pipe and
the OUTLET is the top of the rocker cover to the air
filter.

OK. Picked up daughter from Gatwick last night, probably round trip of 150 miles. Checked this morning and no oil dripping from air cleaner.
So I think that sleeving the rocker cover to air filter pipe down to 1/8" has fixed the problem.
Will fit solid oil filler cap when I next go to motor factors/Minor supplier.
Thanks very much - I have been confused by this problem for a long time and have probably changed valve guides needlessly! Although they probably would have needed doing some time!
I see that if a pipe ran from the rocker cover to the carb it presumably is subject to less induction/suction (or is automatically sleeved)? So if I change carbs at any point I need to make sure I get one without a fitting for the pipe!
One thing does puzzle me 'though.... the oil filler cap with the mesh fits snugly into the rocker cover and was solid before I drilled it. How does the air get in? I accept that this is irrelevant in my engines case but it puzzles me!
Thanks again..... Paul

It has two slits just below the grip which let the air out. If you blow into the hole in the bottom of it you will feel where it comes out of.

Well done Dr.Willie for a successful diagnosis!
And now I know the difference between carb breathers and the air filter breather hose.
I shall check my cars to see what mixed up combinations of both / niether that they have!!
One minor point on sleeving the hole down to 1/8"... If the sleeve is long then you'll need a hole a bit bigger than 1/8" to get enough flow as the restriction from a tube is higher than a hole in thin plate of equal diameter.
(easiest solution is to something like a washer, or if your sleeve is between half an inch and an inch, I'd guess you'd want around 3/16th"? If you want to calculate the hole size for a long sleeve you'll need to know various things including the pressures on both sides etc.. and it would become rather tedious)

Thanks Ray, I thought that was a rather good diagnosis too!
You make a good point re the 1/8" hole but I have been
running a sleeved 1/8" for about five years now and have
suffered no apparent side effects. I would imagine that if
it wasn't creating enough of a breathing outlet there would
be problems with leaks around the rocker cover?

yes and no.
pressure relief: If there was significant blow past the piston rings, you could get higher crankcase pressure but otherwise it would be fine.
suction: If the rings are good, the link to the filter will cause some forced breathing. This air circulation is needed to clear condensation from inside the engine, especially the rocker housing. Without regular servicing you could get creamy oil deposits if there isn't enough air flow.
I'm sure your car is well serviced, so it'll be unlikely to get creamy oil. Also the reduction in air flow may well not be big enough to cause a problem anyway.
And also I reckon if you'd had any creamy oil deposits, you'd already have diagnoised it.
On another engine, (like Paul's) the reduced flow may be more of an issue, but it is hard to be sure.

I will check for creamy deposits/blocked breather and update if I get any!
The sleeve is about 5/8" long and probably slightly over 1/8", at the air cleaner end.
I haven't had any problems with creamy deposits before, I change the oil/filter every year on about 2500-6000 miles.
I thought it was a pretty sharp diagnosis too!

regarding the mayonnaise in the filler cap, I was running
two 1098 Minors simultaneously for about eight years and
one, the saloon, always produced mayonnaise. The other,
convertible never did. Since they were cared for identically
I decided that the only difference was that the saloon was
used as my every day car whereas the convertible was,
and still is, used for long runs in good (warm) weather. In
other words it never does a short run and always gets good
and hot. It is the convertible which has the sleeved filter inlet.

Yes, I used to get emulsion in my Rover when I was not using it much during the winter months. I thought it was head gasket trouble but it cleared up when I started using it more.

This sort of mayonnaise is caused by condensation (unlike normal mayonnaise which is caused by eggs and milk ).
Short journeys and the repeated heating and cooling of the air in the engine cause condensation to form. Longer journeys would allow this water vapour more time to escape.

Yes, mine was definately condensation, unlike my old Fiesta that I had in '92 that WAS the head gasket but that was probably the car's best part!!

unlike my old Fiesta that I had in '92

Yeurggg. I've never seen one of the old pushrod Fiestas that didn't leak oil like there's no tomorrow. My sister had two Fiestas and both were a black sticky mess under the bonnet and always came out of thier services feeling like a new car. But only because they had deteriorated so badly in the mean time.

There's been many few fiestas in my family over the years and apart from one miserable non-starting autochoke (early 80's) they all had pretty good drivetrains.
In 96 I bought a cheap 70's fiesta for my sister and it needed much less TLC than my 70's minor (which leaks from the engine, gearbox and diff, similar to many minors). That fiesta cost me £140 and nothing needed replacing in the 2 years we had it, before being sold on for £200. They're not all bad!

Oil leaks are a touchy subject for me - my Minors have ruined my drive despite being parked over big hardboard sheets.
I'm just refitting a gearbox to my 71 saloon with new rear seal and a modified front plate that has a lip seal. After that I have a good donor engine to rebuild - needs no mechanical repairs, it just leaks a lot.