PCV valve

[les]

I’m checking this item, there seems to be what looks like a plunger in the centre of the valve, I think it should be free to move, am I right ? I can’t find an exploded view, which would be helpful.

[firedrake1942]

This is, I think. the Smiths PCV valve like the one on my 1957 948cc Minor.

[svenedin]

Yes, part 34 in the diagram above is a plunger that is free to move against a spring. It is important to note that there is an earlier type and a later type Smiths PCV valve. The later type has a replaceable diaphragm (part 33). The earlier type has a diaphragm that is fused to the top plate and replacements are not available.

Stephen

[les]

Many than thanks to both for the diagram and info. I’ve got no movement at the check valve No 5. Will need to investigate, there looks like a type of circlip holding the centre assembly to the main body. Not sure it’s dismantleable though.

[svenedin]

Many than thanks to both for the diagram and info. I’ve got no movement at the check valve No 5. Will need to investigate, there looks like a type of circlip holding the centre assembly to the main body. Not sure it’s dismantleable though.

That check valve tends to gum up with tarry oily fluid and if your valve has not been used for a long time this is what I would suspect. Carburettor cleaner dissolves this gunk very well. If that fails try soaking in fresh petrol.

Stephen

[les]

Sounds like a plan Stephen, that’s my next move then.

[svenedin]

By the way, the purpose of the check valve is to prevent an explosion if the car backfired into the inlet manifold AND there was no metal gauze/wire wool in the oil separator chimney. the gauze is not just to help separate out the oil but also acts as a flame front arrestor as in the Davy Lamp.

Stephen

[les]

[les]

As an update ——The check valve is now free to move, I’d still like to dismantle further to clean inside but I’ll see. I’ve blown down towards the valve and it seals pretty well, if I blown very hard air does seep past but I feel it’s functioning ok.

[svenedin]

Good job!

Stephen

[moggiethouable]

Just as a point of interest, I first discovered one of these in a MK111 Triumph Spitfire around 1978, the rubber diaphragm had the tiniest of splits in it.
Caused no end of trouble diagnosing it, I have never forgotten it and never forgiven it.

[svenedin]

Just as a point of interest, I first discovered one of these in a MK111 Triumph Spitfire around 1978, the rubber diaphragm had the tiniest of splits in it.
Caused no end of trouble diagnosing it, I have never forgotten it and never forgiven it.

Yes. I too have had a split in the diaphragm. It causes an air leak, a weak fuel mixture and very rough running. I suspected the diaphragm quite quickly but I could not see the split on first inspection. This caused a lot of confusion. Eventually, I held the diaphragm up against a bright light and I could see the split.

Stephen