[Brad.Jones]

I am sure you have seen videos like the following:
https://www.youtube.com/watch?v=TrKINFBsQD8

Just after peoples thoughts.

Has anyone done it? and what was the result? how long did it last?

Or am I just better off spending more money now at the machine shop instead of later down the track...

[Daves4wd]

Ya get what ya pay for I reckon...

[Mike57]

I have seen my grandfather doing this by hand when I was really young. It was very common to have to do this to cars in the 1920's and 30's but with modern fuels and especially computer controlled ignition and fuel controls it is not that common to see this being done. My guess is it works fine but I question whether you would need to do this to a modern engine much. I suppose if you had the head apart for some other reason you might give it a go.

[jdk81]

I lapped the valves on the head of my sierra.
I did it prior to swapping valve stem seals, initially started by hand, and moved to using the drill.

The valves weren't seating correctly, combination of bent valves, carbon and other contaminants on valve seats from use and being stored incorrectly.
I whacked in 2nd hand near new valves from a different head and lapped them in.

In my car now and works fine

[tonyevans]

What do you think they do in a engine shop that is different? They still lap in valves by using grinding paste and rotate the valves in the set just the method of rotating changes - If I have the head off an engine I clean the valves and ports then lap the valves as a matter of course.

[jdk81]

+1
Machine shop may cut the valves, but then still have to lap them in, and I doubt they lap them in by hand.

As I said previously, I tried lapping them in.
After lapping, I could inspect the seating the region, to ensure there will be a good seal.

If there is enough seating contact after the DIY lapping, getting the seats cut isnt required.

If valve seat cutting is required after a DIY lapping, you can save $ by lapping yourself.