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[JamesV6CDX]

So I have lapped all of the 24 valves in my cylinder head. And have refitted them all.

To test that they are seating correctly, I have filled the ports with paraffin, and have left it some time.

All of the valves are sealed correctly, apart from the no1 exhaust valve. I've tried a couple of times now carefully lapping again with some fine paste, but when I refit it and fill the port, the fluid gently drips out from the valve seat.

There is a nice clean ring around the valve from lapping as expected. There is also one in the seat, although less so - the seat is more shiny.

I can't refit it in this condition, as it would lose compression (and being a diesel it relies on this more than a petrol) - and also might cause it to burn out early.

Any ideas? I'm just off to Halfords to buy some more paste 

I guess in reality I could take it to the machine shop, I doubt it'd be too expensive just to fit one new seat.... but I've got 23 of them to seat properly... surely I can sort the last one?

Had to walk away for a bit, back aches from leaning over it and I'm getting fed up with it 

[Bigron]

Is it possible that you might have got a slightly larger particle of carborundum in the first coarse grind and the fine paste hasn't yet polished it out? You would need an eyemaker's watch glass to inspect it closely, to check.....

Ron.

[X30XE]

Are you testing it with the valve spring in place?

[Doctor Gollum]

Good point well presented...

[Shackeng]

Are you testing it with the valve spring in place?

I can see James' point, if the others, spring loaded or not, seal OK, why doesn't this one?
Knowing James, he will have numbered the valves and used the same ones. Just a thought James, could there be any possible distortion in either the valve or guide, allowing the valve to sit slightly askew on its seat, and yet, because of rotation while lapping, both valve and seat have the correct polished ring?

[zirk]

could be the vaive itself is very slightly bent, only takes a few thou, grinding it in gives the impression all is well due to the circular motion, proof of the pudding would be to fit the valve on another position and retest.

[JamesV6CDX]

To answer the questions

- yes, testing with valve spring installed

- i would always number valves during a rebuild. But I'm this instance (I won't bore you with why) the valves being installed in this head are all known good valves from my old head. So they are all "foreign" which I know is why it's taken a while to seat some.

Coarse paste is usually a no no on modern heads. I tried it on this valve and it made it WORSE.  So fine paste only......

[X30XE]

Then the options I can think of are :
- Valve stem is bent
- Valve guide is misaligned (unlikely I would suspect)
- Valve head isn't perfectly circular
- Valve seat isn't perfectly circular
- Valve seat isn't flat
- You haven't ground it far enough

- any combination of the above

[JamesV6CDX]

Is "ground too far" an option?

[X30XE]

Is "ground too far" an option?

I doubt it. Unless you have the patience of a saint.

Seriously though, unless you've worn completely through the seating areas to find a piece of metal that is no longer round, or even more unlikely, ground it to the point that something else binds up before the surfaces mate... then I very much doubt it. 

Edit : Oh yeah, the other one I missed is cracked valve seat/head

[JamesV6CDX]

I did another careful grind with fine paste for a bit.

So far ten minutes and drip free.

Trying to decide if I can see a slight shine of fluid around the circumference but you could go around the bend looking too closely.

I think if it's still drip free in an hour I will take the "fit and forget" approach with this head

[JamesV6CDX]

To be fair when I first tested it, before starting work, it resembled a sprinkler system - and still ran on all 6 

[Bigron]

James, I do know what a perfectionist you are, but there comes a time when even you have to stop! 

Ron.

[Marks DTM Calib]

You can use coarse paste, no issues but the valves need to seal properly

[JamesV6CDX]

Still fluid tight