Valve head size

MikeT · Post by **MikeT** » Sun Nov 11, 2007 6:56 pm

I don't see it specified in the Haynes BoL. I'm interested to know what the standard exhaust valve head diameters are.

CitroXim · Post by **CitroXim** » Mon Nov 12, 2007 12:35 pm

Mike,

I can tell you when I get home...

How accurate do you need it?

MikeT · Post by **MikeT** » Mon Nov 12, 2007 4:04 pm

Hi Jim,

To the nearest 0.5mm please or better? Have you still got Andy's broken head in your garage?

CitroXim · Post by **CitroXim** » Mon Nov 12, 2007 4:56 pm

MikeT wrote:Hi Jim,

To the nearest 0.5mm please or better? Have you still got Andy's broken head in your garage?

Yes I have, both of them!

32.5mm is what I measure with my calipers.

Give me a bit more time to rummage in my stash and I'll get a micrometer on to it...

Tells us Mike..

What are you up to?

MikeT · Post by **MikeT** » Mon Nov 12, 2007 6:48 pm

Does the thought of xantia head removal/replacement make your blood run cold now Jim?

or are you chomping on the bit to do it again?

I'm thinking if it's worth servicing mine before I actually have to (or worse!), if you know what I mean?

CitroXim · Post by **CitroXim** » Mon Nov 12, 2007 9:14 pm

MikeT wrote:Does the thought of xantia head removal/replacement make your blood run cold now Jim? or are you chomping on the bit to do it again?

Nah, walk in the park....

Personally Mike, I see where you're coming from but my thought is to let sleeping dogs lie. If there is not a problem, then don't try to fix it.

I've pondered and debated this myself, knowing XUD head gaskets usually "go" around the 110,000 to 150,000 mark and thinking a pre-emptive strike may be a good idea but this is my plan.

Whlist the car is running well and using no water/not overheating/not showing any signs of coolant pressurisation, leave well alone. As soon as any of the above show up and the cause is irrefutable the HG beinnning to go (and I understand they give a good deal of warning) then go, do. That way you'll just need a light clean-up skim, a new gasket set and a days work, knowing all is still good and will be again for another 150,000 miles. Most important this is look after your cooling system. I'm convinced that a great proportion of HG failures are precipitated by poor cooling systems, either sick rads or cooling fan faults.

My old TD is on 190,000 still on its original HG. Touch wood....

MikeT · Post by **MikeT** » Mon Nov 12, 2007 9:39 pm

citrojim wrote:
MikeT wrote:... the thought of xantia head removal/replacement...
Nah, walk in the park....

Personally Mike, I see where you're coming from but my thought is to let sleeping dogs lie. If there is not a problem, then don't try to fix it.

But Jim, I think there is a problem - it's not breathing as well as it could.

but as long as I do get a fair warning of failure, I guess I could leave it.

CitroXim · Post by **CitroXim** » Mon Nov 12, 2007 10:04 pm

On the breathing side Mike, there is a bottleneckand it's not so much the head but the exhaust manifold I think.

The inlet tract is great, big valves, nice open ports, as smooth as silk all the way from the intercooler down to the valve. The exhaust ports themselves are OK but when you see what they exit into then the probelm becomes apparant.

As soon as the exhaust gas hits the manifold, it has to turn through a sharp 90 degree bend about 3/4" into the manifold and flow down to the turbo turbine. If you look into the manifold from the port-side, you literally face straight into a wall; the exhaust gas hits this head on, knocks itself out and has to then pick itself up and try to continue on to the turbine.

Then we come to the turbine itself. It is seriously tiny. I surmise that the small turbo and the cat do compromise flow and it is only made up for by the fact that the engine is turbocharged.

This compromise may be slightly deliberate as exhaust scavenging may not be optimum and as a result may even introduce a little EGR to help keep NOx emissions lower. Not forgetting also that the whole shooting-match is desigend to fit in rather a small space at the back of the engine bay. The engine being canted over does little to help in this respect. The engine sits well back in the bay, presumably to firstly help weight distribution and to go with the fact that the bay will take a V6 in there on the same mounts.

Rather than head mods, I reckon the best scheme would be a good tubular exhaust manifold to improve exhaust flow

There's a person over on the 205GTi forum who has tuned a 1.9TD to give massive (albeit unreliable) power. I'll try and see if he did anything special on the exhaust side of things.

MikeT · Post by **MikeT** » Tue Nov 13, 2007 9:27 am

Oh

That's not good. I wonder what alternatives others have come up with. There is a custom exhaust manufacturer nearby but I dont' know if they make manifolds. They'll surely know someone that does so would be worth popping in there for a chat.