Moparts Tech Archive
First time valve lappingWhat am I looking for?
I'm just trying to clean up a set of low mileage heads that have been sitting a couple of years, I'm NOT trying to cut new seats!
If it makes a difference, the heads are 346's.
Are you grinding or lapping??
Lapping is ussaully done with a 'lapping' compound.
And you just need to lap untill you see a nice pattern around the seat and valve head.
on a street motor about an 1/8th inch wide.
What I've always done is to use 'Clover' brand compound. The can has 2 ends, 1 for course and 1 for fine. Just like sanding,start with the course and sort of half rotate the valve with the suction cup tool you bought with the round wood handle. 1/2 or so turn 1 way then 1/2 or so the other. When you are starting to see pattern .100 inch mininum, start useing the fine stuff the same way. How long? Until it's done, some of the valves may work in faster than others.
So, do you lap them after they are ground, or is it even necessary after a grind ??
Now with the new style valve machines that are out and the cutters they use it's not really necessry to lap them now, esp when using new valves.
I will still usully lap them just to see the seat area on the valve and check the width of it.
A sunnen machine like below makes valve jobs a breeze!!!
i always used a cordless drill set on the lowest speed and just chuck the valve up like you would a drill bit and hold it against the seat then pull the trigger and let the drill do the work.
I always use the drill too.
It's reciprocating and progressive if it's like mine. ZIM is the name that comes to mind. Good as long as heads haven't been run very long. I always prussian blue, then lap everytime, but then I have an old sioux valve and seat refacer also. Older than sin but works great. On the valve face I look for uniform width about 1/3 the size of the valve face, favoring the chamber side but leaving a distinct ring below the contact mark. Don't run the seat too close to the edge or you'll burn and split an exhaust valve from lack of cooling. Believe it or not the valve seat tends to help cool the valve by pulling heat off it into the head.