Date: Sun, 22 Dec 1996 23:34:55 -0800 (PST)
From: Mike West <mwest@cdsnet.net>
Subject: Lapping the Valves

>Mike:   
>
>
>     One last question (for now! :-)) What exactly is lapping the 
>valves.  And for new heads, what do I have to do to the valves?  You 
>mentioned a valve job was required even for new heads.
>
>Thanks 
>Mariano
>
>

 OK my man we will lap some valves.  :-)

 I keep meaning to save this post and don't so I have to do again,

 First some cautions: you have to disassemble the valves and springs
and keepers etc.Make sure that every valve is kept with the seat it
came out of, they may not seat so well in the other seats.

 The new exhaust valves tho, will need this lapping to get them to seat
properly.

 Test your springs by squeezing them all with your hand, you should barely
be able to move them and they should all be about the same
stiffness. If they're not then you replace.

 That's not a scientific way to check but it's better than no check at all.

 Now you need to go to the shop and get some "lapping compound" and 
a lapping tool.

 Lapping compound is a medium grit grinding compound, like rubbing
compound only coarser. Some is water based and some is grease based.
I like grease but it's your choice.

 The lapping tool is a stick with a suction cup on it.

 You also may need some "prussian blue" or machinists lay-out blue.

 The first comes in a little tube and I'd pass if the price were too
high. The second should come in a spray can or small can with a brush.

 You set the head up-side down and take the valve that is going in a 
particular seat and put a little lapping compound on the seating area.

 Don't get in the stem guide.

 Lower the valve into the valve seat and put the lapping tool on the 
head. Then with a light pressure, put the stick between your palms
and twirl the stick/valve back and forth in the seat.

 Pick the valve up by the lapping tool and turn backwards a few times.

 This pulls the lapping compound back into the valve seat.

 Set it back down and repeat the lapping again.  You see?

 We are making this valve fit this seat exactly.

 Now pull it out and wipe off the lapping compound on both the seat 
and the valve.

 Examine both, you're looking for a line where the lapping compound 
ground them and the line should go all the way around on both parts.

 Repeat the lapping until it does go all the way around.

 When you think you have it, you use the bluing.

 If lay-out blue, spray or paint the valve and let dry.
If prussian blue put a light film of blue all the way around on the 
valve seat of the valve. This won't dry so you can get right to it.

 Slide the valve back in the guide and lightly twirl it in the seat.

 Take it back out and examine the seats on both parts.

 On the valve, it will show a line where it rubbed off, thats your 
seal.
On the seat in the head, it will show blue that was rubbed on, and 
that's your seal.

 The lay-out blue will just show on the seat it was rubbed off of.

 A shiny line all the way around.

 This line should be at least 1/32" wide.

 You have just lapped a valve.

 Get all the lapping compound cleaned up and go on to the next one.

 When you have done them all and re-assembled the valves,springs etc.
(don't forget the stem seals), then you can tip the heads up on end
or side and fill the inlet or exhaust port clear full of gasoline or 
some other solvent and check for leaks around the valve seats in the
combustion chamber.

 Some people let them set overnight that way and check the next day 
for weeping.

 It is relatively important they make a good seal each and every time.

 Now we talk new heads: new heads are ground with a stone with a 
guide thru the valve guide. The new valves are ground in a lathe type
setup. They never see each other until assembled.

 Maybe they're seating and maybe they're not.

 You'll never know until it's too late.

 If you feel it's too much trouble, at least do the leak test with the
solvent in the inlet/exhaust.

 What will still happen is that the new seats are ground to two 
different angles and form a knife edge seat.

 They will need adjusting 10 minutes after you start the engine up 
and keep right on needing adjustment until they have pounded themselves a
nice wide seat in there. That 1/32" or more, remember?

 So much for the quick question hey?  :-)

 It reads a lot faster than doing the valve job tho.  

 You'll be on the road in no time! (stolen)  

 west