Morris Minor Owners Club

Exactly, there were several different systems used on the Minors, depending on air pollution awareness which grew over the years. For each type there is only one way to be 'correct to factory specification.'
Any Minor with the tappet chest cover breathing in to the CARB should have the filtered type of oil filler cap.
BMC, my cap hasn't 'worn out' but the retaining strap has long gone.

Isn't the vented filler cap supposed to replaced during a main service (12,000 miles?). I guess it was expected it would get clogged up after a while.

Yes, it should have 'replace after 12000 miles' on it which seems totally
unecessary to me since it is there to prevent harmful items being sucked into the engine and can be washed quite easily in white spirit etc.

Dragging this kicking and screaming by the hair back to my problem... Had the swan neck off today and it's clear as a bell! Makes no difference taking the cap off although engine slows a little if I plug either the rocker cover or swan neck breathers. I've also noticed a tiny bit of pinking under heavy load and it's started coughing when cold and again heavy under load, once it's hot no problems apart frm the pink and the smell of burning oil! Could it be a valve seat giving out?

I am getting confused here, earlier in this discussion you said that your
breather came from the timing chain cover. Now you are mentioning the tappet chest pipe. Which do you have? If there is a timing chain breather then it should go to the CARB not the air filter. Regardless of which type you have, since you say the pipes are all clear and assuming
that you only have the 1/8" hole in the air filter inlet pipe i would suggest that you need to do a compression check to see if one or more of your cylinder is pumping straight into the crankcase.

I corrected myself Willie if you read back, it's the swan neck from the chest cover.

Excessive oil fume in the inlet tract will cause 'pinking' because it seriously lowers the octane rating of the ingoing charge. Don't let it pink - retard the ignition timing slightly.

Ok I know this has been gone over loads of times, but please be patient with me.

My 70 1098 had a can on the tappet cover pointing up wards connected to the carb and a vented cap on the rocker box. It worked very well and no gunge in the rocker cover.

However, my 948 has an open pipe on the tappet cover pointing down, a vent on the rocker cover connected to the carb and a sealed cap. And the rocker cover was already showing signs of mayonaise after 500 miles!

Can I improve the breathing? How about a vented cap to improve the airflow in the rocker cover? Or is it due to the oil I'm using at the moment. Running in this engine I have used Comma 20/50. In the last car I used proper Castrol 20/50.

The engine runs at a good temp and most of my runs have been more than 20 miles so it is warming up properly.

Any suggestions as to how to stop the build up of mayonaise would be appreciated.

Roger.

Really shouldn't be a problem with that arrrangement - I wouldn't blame the comma oil - but you could try a change. May possibly point to a problem developing in the engine. Are the 20 miles 'hard driven' or just gentle motoring ?

RogerRust wrote:The engine runs at a good temp and most of my runs have been more than 20 miles so it is warming up properly.

Any suggestions as to how to stop the build up of mayonaise would be appreciated.

Roger.

What thermostat have you got? Mine used to suffer from bad mayonaise but have now fitted 82deg thermostat & no more probs - some recommend an 88 deg one; should also uprate the rad cap to 14lb

Rog

Ah, thats a thought when I first ran the engine it ran hot so I put a cooler 74 deg stat in. Now I have sorted the mixture and timing I can change it back to the 82deg stat.

Well done Rog

ROGER This is where you must be accurate. You say it has a solid oil filler cap, a
tappet chest pipe and a rocker pipe which feeds the CARB do you mean the AIR FILTER? because that is where it should breath to with your system. The mayonnaise is a problem with many Minors and does not mean that your head gasket has gone. I have said before that I owned two Minors,both 1098, both used for the same annual mileage, etc etc but one always produced mayonnaise and the other never did. This was over a ten year period and t here was nothing wrong with either car. There was a mod suggested which involved making a deflector plate which protected the front of the rocker box from incoming air, i made it and it made no difference whatsoever!

I too have seen same spec A series engines with and without gunge - I recall it used to be attributed to worn bores/rings and was used as an indicator of condition. I don't remember seeing it on new/moderateley new cars (referring to the mid-late 60's). Clearly it is important to get the right breathing set up however where previous owners have replaced/swapped parts about.