Blowing oil in Shetland

[Z320]

David,

some photos of your PCV valve could be usefull.

On my photo you see the rubber membran.

The coned valve pin is fixed on the steel disc and may glue there by oil without problem.

But the rubber membran must not glue in the steel disc cover.

 

[stuart]

When I properly fitted the PCV to my 250 (It was there but not actually doing anything) it worked really well and stopped oil being ejected from the filler cap etc.

Stuart.

 

[Lebro]

Just checked mine, all well, but gave it a good clean anyway.

Bob

[qkingston]

Hi Rich, no the diaphragm is there (and fairly new - can't see any splits in it). The plastic I'm referring to is like when you buy a sheet of metal and it has a protective plastic film on it. When I got the new metal disc it had a protective film on the top surface which I took off, but I didn't notice one on the underside. When I took the disc off to have a look inside the PCV it was partially loose, and maybe, just maybe it had been blocking the wee vent hole....

David

[qkingston]

A couple of pics of my PCV, in the 1st one, the metal disc I was referring to is on the rocker cover. Does that help at all?

David

[Z320]

Hi David,

on the 2nd photo, why does the steel shim with the valve pin not flip out?

There must be a spring between. I could not make such a photo.

And you have an aluminium cover fitted, very likely without oil seperator baffle, not at all like on the original steel cover.

This allows more oil going to the PCV valve (to be seperated there), perhaps too much?

Ciao, Marco

Edited June 22 by Z320

[mark canaday]

IMHO there is no way oil exits the exhaust. It must be coolant. 

On the idea of valve stem seals, they cause excessive wear of the guides in time. The solution is to

knurl the old guides when fitting new valves. This has the effect of holding the oil in the guide and 

making 12 to 15 hundred miles /qt consumption a reality.

MD

[qkingston]

On 6/22/2026 at 5:09 PM, Z320 said:

Hi David,

on the 2nd photo, why does the steel shim with the valve pin not flip out?

There must be a spring between. I could not make such a photo.

And you have an aluminium cover fitted, very likely without oil seperator baffle, not at all like on the original steel cover.

This allows more oil going to the PCV valve (to be seperated there), perhaps too much?

Ciao, Marco

Hi Marco, yes there is a spring underneath the Valve pin. The cover plate is the only one I could find when I fitted the PCV (mine was missing - removed by PO), does that make a difference? Also I have fitted a replacement diaphragm and the previous symptoms seem to have disappeared!! Would that make sense? Also the vented oil filler cap (as seen in the photos above) is the only one I could find that fitted the Triumphtune rocker cover. I did get a refurbished original filler cap from Rich C-R, but the fitting was different and I had to return it  . I assume the vent hole in the filler cap I have is adequate to allow the crank breathing to work properly??

Regards

David

[Lebro]

25 minutes ago, qkingston said:

Hi Marco, yes there is a spring underneath the Valve pin. The cover plate is the only one I could find when I fitted the PCV (mine was missing - removed by PO), does that make a difference? Also I have fitted a replacement diaphragm and the previous symptoms seem to have disappeared!! Would that make sense? Also the vented oil filler cap (as seen in the photos above) is the only one I could find that fitted the Triumphtune rocker cover. I did get a refurbished original filler cap from Rich C-R, but the fitting was different and I had to return it  . I assume the vent hole in the filler cap I have is adequate to allow the crank breathing to work properly??

Regards

David

The cover plate for the PCV looks correct, with the cross in the center, 

Also, a vented oil filler cap is correct, it's to let fresh air into the engine. Only works as it should with no snorkle  breather.

Bob

[Dale Moore]

The hole in your cap is not as big as an original one, it's better than nothing

Dale

[Z320]

Hi David,

the PCV valve reduces the vacuum of the inlet manifold to suck moderate the vapors out of the engine.

With a not vented oil filler cap the vacuum in the rocker cover was always about 60 mm water column with my repro PCV valve.

This is not much, just enough to suck a slack oil filler cap on the valve cover.

Try this on your engine, what happens?

I drove long time a not vented oil filler cap, until I was able to buy an original vented one.

With the vented cap the engine runs better on idle, this may meen the carbs are adjusted too rich?

I hope this helps.

Ciao, Marco

[Lebro]

2 hours ago, Dale  Moore said:

The hole in your cap is not as big as an original one, it's better than nothing

Dale

It looks to be the same size as in my valve - perhaps yours has been opened up ?

Bob

[Dale Moore]

Supplied courtesy of Richard last year  Not with the car ATM, but I guess the hole is 3mm or thereabouts 

Edit  Ah Are we talking about the pcv valve cap Bob?

Edited June 24 by Dale  Moore

[Lebro]

I thought we were !

Bob

[Z320]

Diamater of the hole in my original vented oil filler cap is 3.0 mm,

of the hole in the PCV top cover (repro) is 2.1 mm.

The size of the hole in the PCV top cover IMO has influence on how it works.

It is the resistance to let the athmosphere / air in on top of the membran.

I made a test mit a d = 8 or 10 mm center hole some years ago, to see how it works and to lock it manual to see the infuence on the carbs.

With the  big hole it makes ugly noises.

The video is on youTube

 

Edited June 25 by Z320

[qkingston]

Thank you for all your replies. It seems the PCV set up is correct, particulary noting Marco's helpful videos. The vented oil filler cap also seems ok; as I said, I would have fitted the original from Rich except the fitting doesn't match on the Triumphtune rocker cover. I'll run with what I've got, it's been ok for 4000 or so miles, it was only during the longer Shetlands trip that I started to notice this issue. With a replacement diaphragm (even tho I can't see any damage to the one being replaced), things seem to be ok

One to monitor

Regards

David