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First time valve lapping

What am I looking for?

Moparts Member
Posts: 3372
From: Somewhere between Houston & Galveston, TX
Registered: Nov 1999
posted 05-20-2002 06:24 PM

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!
I understand the basic principles, but what am I looking for in the way of a pattern when I'm done? For that matter, how much time should I spend on each valve doing this? A few quick spins with each grit, or a minute or so?

If it makes a difference, the heads are 346's.

Suggestions? Tips?



Posts: 8736
From: Ohio
Registered: Nov 1999
posted 05-20-2002 06:29 PM

Are you grinding or lapping??
Sounds like you're grinding.

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.


Moparts Member
Posts: 852
From: Casa Grande, Arizona, USA
Registered: Nov 1999
posted 05-20-2002 09:42 PM

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.


Moparts Member
Posts: 3593
From: Sicamous, B.C., CANADA
Registered: Sep 2001
posted 05-21-2002 03:41 AM

So, do you lap them after they are ground, or is it even necessary after a grind ??


Posts: 8736
From: Ohio
Registered: Nov 1999
posted 05-21-2002 03:58 AM
In the ole days !! LOL
On a standard type valve job when all we had was stones and sand paper they always got lapped on a valve job.

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!!!
This one is Kammers.


Moparts Member
Posts: 900
From: Ohio
Registered: Jul 2000
posted 05-21-2002 10:56 AM

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.


Moparts Member
Posts: 5689
From: Detroit suburbs MI USA
Registered: Jan 2000
posted 05-21-2002 11:21 AM

I always use the drill too.


New Member
Posts: 88
From: Findlay ,Ohio
Registered: Apr 2001
posted 05-21-2002 05:27 PM

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.


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