Morris Minor Owners Club

I'm in the process of replacing the gasket on the tappet chest cover on my 1969 traveller. The engine is a recon which I fitted back in the late 90's.When ordering the new gasket I noticed that the cover, which has a concave surface, (see pic) was not the same as illustrated in the Haynes manual/ESM graphic. I also noticed that the pipe with a filter is connected directly to the top of the manifold see pic 2, with a flat disc containing a filter.

So this looks like the pressure from the tappet chest is relieved by allowing the air to pass out through the pipe, gets filtered before being expelled through the manifold. I'd appreciate it if someone can confirm if this is correct and if this is an old design which was superceded by the simple crankcase vent pipe shown on the Haynes graphic?

Thanks in advance

You have something of a rarity there! I see from your post that this is a replacement engine. Can you confirm the first part of the engine serial number please. Is it 10ME?

That type of manifold is designed for a Smiths PCV valve. You have the spigot and the bracket for the valve.

The later tappet chest covers are concave, earlier ones (948cc) are convex. The concave type uses a neoprene gasket and a cup washer and seal under the head of the bolt that secures the cover.

My car has exactly this system and it would look like this.......

See this very recent thread which list the relevant gasket and seal part numbers: viewtopic.php?p=697951&hilit=tappet+chest#p697951

Be aware that the chimney oil separator attached the tappet chest cover is often blocked. It contains a type of wire wool that corrodes and gets totally blocked making the engine breathing system inoperative. See if you can blow easily through the hole in the top of the chimney. If not or if there is resistance, you need to clean it out. This involves pulling out the corroded wire wool with long forceps or pushing it out with a screwdriver and then refilling the chimney canister with stainless steel pot scourer. It must be stainless steel and definitely not a Brillo pad with soap! viewtopic.php?p=697912&hilit=oil+separator#p697912

Stephen

You have the later cam follower (tappet) access covers which use a neoprene/rubber gasket.
The canister is a oil separator and has a gauze element inside to separate the oil from the crankcase fumes.
The disc on top of the manifold is a Pollution Control Valve (PCV) which allows the fumes from the engine to be drawn into the manifold and consumed in the combustion chamber.

philthehill wrote: ↑Fri Apr 19, 2024 9:33 am You have the later cam follower (tappet) access covers which use a neoprene/rubber gasket.
The canister is a oil separator and has a gauze element inside to separate the oil from the crankcase fumes.
The disc on top of the manifold is a Pollution Control Valve (PCV) which allows the fumes from the engine to be drawn into the manifold and consumed in the combustion chamber.

I would argue Phil that PCV stands for "positive crankcase ventilation".......

https://en.wikipedia.org/wiki/Crankcase ... ion_system

https://mgaguru.com/mgtech/engine/cv103 ... 20valve%22.

You can call the valve what you like but the valve was fitted for the control of pollution caused by piston blow past escaping from the crankcase.
It has been called a pollution control valve for many years without dissent.
The valve is designed to creates a negative pressure in the crankcase.

philthehill wrote: ↑Fri Apr 19, 2024 9:53 am You can call the valve what you like but the valve was fitted for the control of pollution caused by piston blow past escaping from the crankcase.
It has been called a pollution control valve for many years without dissent.
The valve is designed to creates a negative pressure in the crankcase.

Yes Phil, you know I am well aware what it is for! Never mind.

Stephen

According to the Parts List, it wasn't a PCV, it was a VBC.... Valve - breather control ...

For some reason, the pdf I have of the AKD 3541 doesn't have the illustration to go with the list, I guess that page had been lost, but the parts are listed.....

So as Phil suggests, we can call it what we want then!

Thanks all for the valuable information. The engine doesn't have a number on it, the plate was ground off when I bought it. Thanks for the info on the set up and the advice on cleaning out the oil separator. I'm happy to use the 3 letter acronym, at least I now know it has a useful purpose.

If I've understood things correctly I can assume that the engine is of a later type, is there any way of identifying exactly when the PCV/VBC was introduced into the engine design??
This info is really helpful so thanks everyone. Bob.

For many years, it has been referred to as a pollution control valve without any objections.

TomBrooks wrote: ↑Wed Jan 21, 2026 8:02 am For many years, it has been referred to as a pollution control valve without any objections.

Yes I've heard it called that but that is not its purpose really unless oil leaks are pollution which I suppose they are! By reducing the crankcase pressure the engine is less likely to leak oil especially from the rear scroll and water is removed effectively from the oil. There were various different engine breather arrangements for the A-series engine in the Minor. The most well known is the pipe from the rocker cover to the air cleaner and a swan-neck breather tube on the tappet chest cover with an extension pipe on the stud that would be where a mechanical fuel pump was fitted if a Minor had one (which it doesn't because it has an electric pump). In that system the tappet cover pipe is an inlet for fresh air (very often blocked) and the fumes are drawn from rocker cover to air cleaner. Some engines of the era did vent crankcase fumes to atmosphere which creates unpleasant smells and does pollute air so I suppose in certain cars it could be considered a pollution control valve. The Smiths PCV valve was used on numerous British cars of the era but is a rarity in the Minor as it was only used for a short time on engines with serial numbers 10MEU. The trouble is, these cars are now rather old and the breather parts are interchangeable so often a car ends up with bits of one system and bits of another or a different engine entirely. Symptoms of a blocked breather system are oil leaks combined with mayonnaise-like deposits in the rocker cover (an emulsion of oil and water where the water vapour has not been vented by the breather system water vapour being a product of combustion).

Stephen

" The most well known is the pipe from the rocker cover to the air cleaner and a swan-neck breather tube on the rocker cover with an extension pipe on the stud that would be where a mechanical fuel pump was fitted"

I think you meant a swan-neck tube from tappet chest. Stephen
Also worth mentioning this system uses a non- vented oil filler cap

Bill_qaz wrote: ↑Wed Jan 21, 2026 10:41 am " The most well known is the pipe from the rocker cover to the air cleaner and a swan-neck breather tube on the rocker cover with an extension pipe on the stud that would be where a mechanical fuel pump was fitted"

I think you meant a swan-neck tube from tappet chest. Stephen
Also worth mentioning this system uses a non- vented oil filler cap

Yes Bill I did mean that. I actually spotted that error and corrected it but I did not save the edit. I have corrected it now.

Stephen

Just to add to the confusion - if your engine is in good condition it does not matter if you have a vented or non vented oil filler cap.
If your engine is in poor condition then it does matter what oil filler cap you have fitted and which must be commensurate with the breathing system fitted.
Also the various breather systems are there to compensate for engines in poor condition or for more importantly when they get to a poor condition.
Engines in good condition and set up right do not pollute to any degree of concern.

Just to be different my breather exits the tappet chest cover, goes through the cylindrical oil separator and then in to the air filter. There is no provision for a PCV on the inlet manifold and I think the oil cap is of the vented type.

Mayonnaise has all but gone after cleaning out the oil separator.

michael4 wrote: ↑Wed Jan 21, 2026 4:19 pm Just to be different my breather exits the tappet chest cover, goes through the cylindrical oil separator and then in to the air filter. There is no provision for a PCV on the inlet manifold and I think the oil cap is of the vented type.

Mayonnaise has all but gone after cleaning out the oil separator.

Some of the very late Minors had a version of the HS2 carburettor with an inlet stub pipe. The breather pipe was connected from oil separator to carburettor breather inlet.

Stephen

I agree with Stephen, the PCV was originally designed to reduce or stop oil leaks from engines which were past their best through a positive crankcase ventilation. In the pre-polution era