LAPPING VALVES

You grind the valves on the proper angle and you grind the seats on the proper angle and then you lap them to see if the width of the seat is correct and in the proper place on the valve. If it isn't then you have to use different angle stones to move the seating area up or down or to narrow the seat width. Modern machine shops have cutters that will do a 3 step valve job basically all in one operation. If you want a good valve job take it to one of these places. If you want a half azz job lap them.
 
It assures that the seal is even all around.

While grinding should allow a perfect seal there are variables that make lapping the best way to go.
 
lapping valves is so obsolete. it was to get the valve seated because the seat and valve face angle were both ground with the same angle (45 degree's ).
valve grinding now has an interference angle of 1/2 degree. the seat is 45 degree's the valve is ground 44 1/2 degree's. this gives a faster seating and if a tiny piece of carbon ever got between it will work its way out.
lapping valves is just not done anymore. that's why in the old days you ended up with a seat as wide as the valve face. the seat has to be positioned in the correct spot on the valve and has a spec for the width. all this is done after you have the valve stems and guides in spec. also.
 
When valve seats are ground they are rough. Lapping smooths them out to seal better. Machining seats and valves is more common now and seats that have been machined seal better and they would suffer if lapped. Neway sells cutters at their website.
 
Automotive machine shops are getting hard to find,and more expensive. They used to be on every other corner,and did good work at good prices. I think many of these old timers are getting out of the business. lha
 
(quoted from post at 14:40:31 10/26/14) When valve seats are ground they are rough. Lapping smooths them out to seal better. Machining seats and valves is more common now and seats that have been machined seal better and they would suffer if lapped. Neway sells cutters at their website.

I don't think so. In 1972 I took my first valve job to a NAPA machinist in Blacksburg VA. He was incensed at the idea that his valve refacing would need lapping to make it seal. He told me to take the valves and heads home, turn them upside down, drop the valves in, and fill the combustion chamber with raw gas. If thy were dry in the morning he would redo the job for free. Come morning they were still full of gas and I have never lapped valves again. Lesson learned. A properly done valve grind does not need to be lapped in.

TOH
 
yes you are 100 percent correct. lapping is from the 1920's and 30's. it is not done today. those that do it are not doing a correct valve job first.
 
I would never hand lap valves when doing a full rebuild. In that case I have the machine shop grind the seats and valves. However, I have done a few in frame rebuilds consisting of just rings and bearings. I do not have access to valve grinding equipment. In that case I hand lap the valves to get a better seal. If you can't get the valves ground then lapping is better than nothing.
 
(quoted from post at 04:49:40 10/27/14)
(quoted from post at 14:40:31 10/26/14) When valve seats are ground they are rough. Lapping smooths them out to seal better. Machining seats and valves is more common now and seats that have been machined seal better and they would suffer if lapped. Neway sells cutters at their website.

I don't think so. In 1972 I took my first valve job to a NAPA machinist in Blacksburg VA. He was incensed at the idea that his valve refacing would need lapping to make it seal. He told me to take the valves and heads home, turn them upside down, drop the valves in, and fill the combustion chamber with raw gas. If thy were dry in the morning he would redo the job for free. Come morning they were still full of gas and I have never lapped valves again. Lesson learned. A properly done valve grind does not need to be lapped in.

TOH

The moral of the story is to check for a seal Lapper-lubber are not...
 

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