PCV

[les]

What one have I got ? I think I read here once, that there are two types, diaphragm not available for one of them.

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[geoberni]

Have a look at this: viewtopic.php?t=69311

[philthehill]

Les
Your PCV is the later type with the replaceable diaphragm which is still available.
https://www.somerfordmini.co.uk/diaphragm-pcv-valve
Phil

[les]

Thank you both for your helpful replies. I’m trying, with little success so far, to dismantle the central mechanism, it is not sealing properly. There is, what appears to be a shallow circlip of sorts, holding the thing together. I can’t seem to get the clip out.
Incidentally from the picture, the diaphragm has a few bulges but no holes or damage.

[philthehill]

Les
If I remember correctly there is nothing under the plate held in place by the shallow circlip. The separate centre is there because of the manufacturing process. If you do manage to get the circlip out you may not get the thing back together.
The centre pin is not an absolutely precision sealing item all you can hope for is a modicum of sealing. You could replace the plate & pin (available from Somerford Mini) or try lapping the pin to the seat to give a better seal.
Phil

[svenedin]

There's a valve in the base which (so I have read) is called a check valve. It only opens one way and is supposed to stop a backfire from igniting the blow-by gases. I don't believe it is meant to come out and I have never attempted to remove it (as you know, my car has a Smiths PCV). What I have done is squirted carburettor cleaner in, given it a good shake and repeated until the cleaner came out clear and not filthy oil colour.

Les: buy a new diaphragm and always carry a spare in the car. If it develops a pinhole the car will suddenly and inexplicably (or so it seems at the time) run lean. This has happened to me and I won't get caught out again. It takes seconds to change the diaphragm and off you go again. I didn't make it to an MoT test due a hole in the diaphragm!

Described in this article: https://mgaguru.com/mgtech/engine/cv103.htm

Stephen

Smiths PCV Assembly.jpg (51.07 KiB) Viewed 2974 times

[les]

There appears to be a moving part under the plate, the check valve ? It does not seal very well, this is my concern. Yes Phil, I’m thinking I might not get things back, it’s probably is not designed to come apart, although I’d like to try. I might give it another flush through before hand. Perhaps I will buy another diaphragm then Stephen.

[svenedin]

The check valve doesn't have to seal perfectly I wouldn't have thought, it just has to restrict a backfire event. It may seal better if the oily stuff is washed out. It's also possible that you blowing through it in no way recreates that kind of pressure that would close it in a backfire!

Stephen

[les]

Thanks, yes Phil and now yourself have mentioned the seal is not perfect, so it’s looking to be a better plan to just give the part another flush through.

[les]

Just as an update, valve flushed again with carb cleaner, ready to fit. The breather system at the moment is from canister to carb.
What would the effect be if I left the arrangement as it is but with the addition of the PCV ? As sketch.

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[svenedin]

I think use either the PCV or the breather inlet at the carb but not both. I didn't realise you had a breather type carb already.

Stephen

[les]

Yes probably a silly idea, it was just a thought that crossed my mind.

[svenedin]

What some people do is use a Y-piece to join two engine "outlets" to one breather pipe going to PCV or carb. E.g. a tappet chest breather AND a rocker cover breather or a tappet chest breather and a timing cover breather. This is of course non-standard on a Minor and I have no idea whether it is effective or useful!

Stephen

[philthehill]

Les
You can always try the two point breather solution. If it does not work out as expected you can always revert to either the carb or PCV solution.
Phil

[les]

Thanks Phil and Stephen, i assume that would be more sensible than the idea I dreamt up ! My aim is as much negative pressure as possible.

[svenedin]

I think what will happen is that the vacuum will be stronger in the pipe connecting to the carb inlet and it will try to pull gases backwards through the PCV to manifold connection. The vacuum in the carb inlet is affected by the the throttle position and engine load but the PCV is more sophisticated and tries to keep a constant small vacuum.

Stephen

[svenedin]

Understood. Is your engine leaking oil badly?

Stephen

[les]

Well yes there is an oil leak but not bad, just annoying. I have been thinking the scroll seal may be the culprit as the leak exits at the bottom of the engine backplate, the gearbox front cover, on inspection with an endoscope appears ok. However whilst changing the manifold the other day, I noticed oil from one of the tappet covers, which perhaps may well have worked its way round to the bottom of the said backplate. I have replaced the gaskets so will see, I did replace the sump gaskets etc a while back in searching for the solution, so again hopefully eliminating that. In desperation I even had a sump guard made as a last resort but would much prefer not to fit it. I’d like an oil free engine like Phil’s, I reckon he must have a Japanese engine in his Minor !!!

[philthehill]

No Japanese engines in my Minor just a very carefully built 'A' Series .
I do not have a crankshaft rear seal just the scroll and there are no devices to lower the crankcase pressure. The crankcase just naturally breathes into a catch tank (with sight glass) that has remained relatively dry ever since it was fitted many years ago.
Greasing the gaskets and cutting the rear cork seal correctly helps considerably. I do have a set of plastic/neoprene rear sump seals but have not fitted them as I find that they are not as flexible or adaptive as the original cork type.
Having the Quaife gearbox with a first motion shaft seal stops the oil coming from the gearbox unlike the Minor gearbox which has return scroll for the first motion shaft - so oil is stopped both ways from entering the bell housing.
Phil

[les]

I wish I had stripped and rebuilt my engine before refitting it. I naively assumed though, being a recently bought Gold seal unit by previous owner, that it would be good. So after the restoration simply refitted it. Lesson learnt !