6 replies to this topic

[Boycie]

Hi all.

 

I'm working on an unleaded head to go on my 998 City.

 

It's a standard CAM4810 one.

 

My problem concerns the exhaust valves.  All seem to have a grey/ green finish to them on the head, which extends onto the seat angle.  This finish is very hard but has chipped away in places, see photo-

 

20180718_145745 by David James, on Flickr

 

This is going to take a hell of a lot of lapping to get smooth!  Is it a problem and are the valves scrap?

 

The inlets don't seem to have this finish/ coating and will lap in correctly.

 

Thanks in advance :)

[cal844]

Could be some form of corrosion or oxidisation?

Edited by cal844, 18 July 2018 - 06:10 PM.

[Spider]

It looks like a coating from leaded fuel.

 

You can have the seats on the valves re-dressed and really, that should be your port of call, not just for these but also the Inlets. I'd also suggest having the tips re-dressed too as the wear from the rockers.

 

You probably should also have the seats in the head re-cut too as they maybe out of shape.

[Boycie]

Thanks both. As I removed further valves, I noticed one seat had flippin great chunk out of it, so the head needs a full recon anyway. No quick 'lap and go' for this one!

[DeadSquare]

It looks like Hammerite to me.

[ACDodd]

That grey simply looks like the last owner had a good with some lapping paste.

Ac

[Boycie]

To be honest, the head is a total 'unknown quantity' to me so anything could have happened to it in the past! It'll stay on the shelf for now I think.