Lapping valves

[Toddy415 1,292]

Does anyone know the correct amount to lap valves? I cant find consistant info or is it personal preference? Some i have found lap the entire face others just do a 2-3mm band around the face. Heads are cast iron off a big block chev. 

Cheers in advance

[piazzanoob 1,492]

just do them until there is a nice clean lap mark all the way round. but you may not get the whole face of the valve seat which is fine. 

another thing to do is put bearing blue on the valve face and let the valve drop on the seat and see how much is contacting.

also valves and seats may need refacing on a machine depending on the wear.

also check the valve guides aren't too worn too 

And make sure the head/valves gets a good clean after lapping them in too 

hope this helps

[Ghostchips 4,878]

If you're asking how much of the closing face needs to be lapped to fit.  It should have a minimum ring, if the seat is cut on 2 angles and the valve face would be lapped for maybe half a mill' or so?
Reason being that sharp edge cuts through carbon, but is still wide enough to dissipate heat.

Obviously i do 1-2 mm on my dinosaurs so maybe you shouldn't take my advice.

Or i answered a different question altogether.

[RUNAMUCK 20,046]

My advise is to draw vertical lines around the seat in vivid so you can see when you've got good contact.

And go easy with the coarse paste. It's quite easy to sink the valve quite deep into the seat. The deeper the valve sits, hurts flow.

 

[SOHC 7,552]

 should be in the manual for the engine