Valve grinding question

[aww999]

Rebuilding/refurbing a 100k+ mile cylinder head for my car. I noticed on strip down that the exhaust seats in the head were quite badly pitted so when I got the head skimmed I them to reface the exhaust valve seats slightly, intake seats are untouched. So now all the seats have a nice shiny finish, and the original valves are pretty much unmarked.

Do I still need to grind each valve in with paste? I have done a couple, and I am a bit concerned that the nice shiny finish on the seat is now a grey looking ridged finish, ie with my fingernail I can feel very slight ridges on the seat surface (the 45deg face of it where the valve actually contacts and the grinding is occurring). Each valve is going back in its original position, and they all need reshimming anyway so that is not a concern.

[dilbert]

The polished surace would have been very smooth and regular, but your existing valves would also have been so. When you bring them together the seat would be matched to the mandrel that made it, and the valve matched to the old seat. As the valve was closed it may only have had minimal contact.

By lapping the valves in, the finish would become poorer, and initially you may have seen a thin grey band representing the contact patch. Ideally the band should be the 90% of the seat width.

If you want a polished seat, then you will need to use finer and finer grades of paste. a smooth seat is possibly better, but not if it's not matched to the valve. The only reason I can think of for a finely polished seat is if you are worried about oxide buildup. Although I'd have thought that the valve action would prevent this to a reasonable degree.

[rev-erend]

I'm not a huge expert in this area but while you have the head apart - check each valve for side play .. indicating a worn guide.

Edited by rev-erend on Monday 21st August 16:08

[Pigeon]

Yes, you do need to grind them in. As Dilbert says, if you don't the chances are they'll only be making contact along a very narrow and possibly discontinuous band. Don't bother with the "coarse" end of the tin, just use the "fine".

For a diesel engine, after reassembling the valves and springs back into the head I prop it up with the manifold face facing upwards and fill the ports with diesel; if any leaks out round the valves I pop that valve out and have another go at it. Don't really need to be so perfectionist with a petrol engine.

[aww999]

Thanks for the responses, that regular grey band is what I'm seeing so it's all good, just wanted to check before I did all 24 . . . !

I've checked all the valves for sideplay in the guide and they are all in spec so new stem seals should be all thats required.

[eliot]

aww999 said:

that regular grey band is what I'm seeing so it's all good, .

Yep, Grey band is what your'e looking for.

[Boosted LS1]

eliot said:

aww999 said:

that regular grey band is what I'm seeing so it's all good, .

Yep, Grey band is what your'e looking for.

Seems hard to achieve with titanium valves.

Boosted.

[rev-erend]

Boosted LS1 said:

eliot said:

aww999 said:

that regular grey band is what I'm seeing so it's all good, .

Yep, Grey band is what your'e looking for.

Seems hard to achieve with titanium valves.

Boosted.

SHOWOFF !

[wedg1e]

Bit late on this one, but a dodge I use is to smear grinding paste on the valve, drop it into place and then fit a cordless drill to the top end of the stem
Keyless chuck obviously, few spins forward, few reverse, and yer Uncle Bob's yer Auntie's Fanny

[GavinPearson]

If you are reusing valves you need to lap them in.

After you have achieved the grey ring, lap using paraffin, but no paste, and keep doing so until the paraffin comes away clean.

Failure to do so will result in you needing to repeat the repair.