Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Workshop Note - GDI Oil Breather

Hi,

A question about the merits of simply venting the PCV to air versus an Oil Catch Can.

From what I can determine the Intake Manifold sucks air from the crankcase, so simply venting via a filter would not work unless there is enough pressure in the crankcase to push the gases/oil out. Even with some pressure in the crankcase it will not be as effective without the suction from the manifold.

So......
- is my understanding correct?
And if so....
- could simply venting cause a build up of oil/water in the crankcase? Which I would assume to b
e bad.

I'm not a mechanic, and have been putting off the job of removing the intake manifold to inspect/clean the valves for some time but given the findings in this thread and Roberts video I think it's time I did. The car has done 39k miles and I used a GDI valve cleaner through the intake at 29k and 34k miles, it will be interesting to see if this has had any effect at all.

Regards

my understanding as yours Mark i.e. fit a catch tank & don't simply vent to atmosphere.

The intake Manifold is now off and its not good news, using Intake Valve cleaner via the air intake doesn't work, they are a mess.



Will clean them manually in the next few days (waiting on Amazon delivery) and put back together.

They are that bad I'm having trouble detecting any movement of the valves to determine when they are open or closed, I'll have to figure it out before squirting the cleaning fluid in, suggestions welcome.


Regards

Bloody hell they look like you are using 2 stroke. Not such a good idea then GDI.
But surely all those Fords & Masdas etc out there would be equally affected & doing more miles there would be a big press on this ?

I did easily find this talking about catch cans & spray cleaners here

Mark, Take the plugs out and set a piston to TDC, well two pistons will be at TDC. You should then be able to see which cylinder has the inlets just open and which has them closed. If you still cannot tel then we'll have to use plan B. But try plan A first.

JohnV6 As I said in the other thread on this subject some (all?) manufacturers now use port and direct injectors.
Cheers
John

I agree with John re finding TDC. Having seen it done in one of the videos during my online research, I used a fairly long screwdriver down the plug hole while carefully and very slowly turning the crank with a ratchet on the front pulley. As long as you make sure the screwdriver is not getting jammed, by checking it is always loose, then it is a good visual way of seeing where a piston is in the cycle.

I appreciate that your valves seem worse than mine were, but looking down the tract while slowly turning the crank as above, I was able to see the valves open and close fairly clearly.

Good luck! And lots of patience...

Keith, You do right to fill in on the bits I missed out. I just assume that eveyone has had a screwdriver trapped between the piston and the plug hole. LoL.

One thing about Mark's photo is how wet the backs of the valves look when compared to your pic?

And I've got all this to do this winter!!!
Cheers
John

Thanks John & Keith

Good tip re TDC that should work fine, I'll try it today.

The valves are not wet, the deposits are just shiny, might be how I took the picture. I poked a dry tissue in and it came out covered in black soot not oily.

Still waiting on a cleaning brush set similar to Keith's, so today I'll remove the PCV short pipe, measure up for the hoses and Catch Can and get them ordered.

Thanks

The system is effectively sealed Mark, and negative crankcase pressure became "a thing" years ago, to contain crankcase oil droplets and arguably to inhibit leaks through the crank seals.My 1967 Midget had a primitive valve set above the inlet manifild, which was a shallow pan shaped metal casing which contained a rubber diaphragm. A pipe came direct from the crankcase into the edge of the valve, which fed vertically down into the inlet manifold between the twin SUs. The valve was kept open by a light spring, but when the manifild depression increased with throttle opening, the valve closed so that no vapours were drawn through. When the diaphragm got a pinhole, the valve fluttered, and it actually sucked oil into the inlet manifold and made a spectacular smoke screen.

The GDi system sucks from the crankcase into the inlet manifold via the narrow bore pipe, and from the cam cover into the inlet tract upstream of the throttle body via a wide bore tube. By disconnecting the pipes, the crankcase will not have negative pressure, but I really don't see this affecting the function of the engine.I tried a catch tank on the cam breather but it stayed clean. On the inlet manifold, space is difficult. Whatever you decide, I don't think it will make much difference, and as John mentioned, some of the deposits will come down the valve stems anyway.

TDC tip works fine and wire brushes delivered early, so have made a start on cleaning 2 sets of valves. It's hard going, been at it all afternoon and just beginning to see the valves. Have left some cleaning fluid in to soak overnight.

A note for anyone else attempting this.
The Inlet Manifold connection was a real pain to disconnect, but on the bench it's easier to see how it comes off, Press in the tabs at the side and Twist the connector Anti Clockwise.

I decided to install a Catch Can, I know it won't solve the inlet valve issue altogether but will help, after this clean I'll leave it about 20k miles and probably have someone else clean them with walnut blasting. I won't bother with any cleaner via the air intake. I don't want to risk a future problem from the crankcase retaining oil & water, I know it's probably a small/very small risk but that's me.

I removed the pipe from the PCV Valve, (Inlet manifold end already off). Have a Catch Can and hoses now ordered to be delivered tomorrow. Looks like it will mount nicely beside the washer bottle.