Is what the machine shop told me true?

Putting on the rubber valve stem seals is a piece of cake.

If you are going to try to lap the valves yourself, put them back in the same hole you took them out of. (This does not mean I recommend you trying to do the valves yourself....do what you want....)

Well he's partly correct. If you just pulled the valves and didn't tag them as to which head and what valve position they were from you would need to do a full valve job.

As long as you keep them in the same holes you won't have a problem. Make SURE you clean up ALL the lapping compound on each valve and clean the stem area as well. Remove the valve stem seals BEFORE you do the lapping step. For a V6 an egg carton works real well to keep the springs, keepers, and other bit in as you take them off.

Sort of. There are two types of valve stem seals used. There is the lower seal that looks like an umbrella. There is also an upper seal on some vehicles, it is a simple O-Ring that goes at the base of the keepers inside the spring retainer.

If you are going to remove the valves yourself, get a cardboard box, on the bottom of the box, poke some holes and let the valve stems drop into the holes.Be sure to draw a sketch on the box so you will know which valves are which.Best to let the shop remove and replace the valve seats, if you want new valve seats. cuhulin

Why should I not lap the valves?

I doubt that engine has replaceable seats. Everything lately has integral induction hardened seats to deal with leadfree gasoline.

Now, a machine shop can cut, or grind and lap in seats that are pretty damaged and that you cannot touch with lapping alone.

Why should I not lap the valves?

************ Lapping is a slow process, using various grades of abrasive. It can help to mate the valve face to the seat.

If, however, you have extensive erosion to the valve face or seat, it can be a slow go.

At the machine shop, they can use a cutter or grinder to face the valves and to clear up the valve seat area. Usually, they will grind the valve and seat at slightly different angles to get a better seal. Even then, they may lap it in a little bit.

Sometimes they will make a three angle cut on the valve face, which was at one time considered state of the art. They can also narrow or widen the valve seating area if need be.

BUT, if your valves and seats look pretty clean, go ahead and lap them with your choice of abrasive... Just be sure to clean it well.

As long as they go back in the same hole, there is no problem. Maybe there is a misunderstanding somwhere, as this is not in the least contrversial. Of course, it may or my not need a valve job, which is a different question altogether. Lapping valves probably doesn't do much one way or another. I do it because I am old, and old-fashioned but I doubt it serve much of a purpose. Can't see it hurting though. As already posted, be sure to clean the abrasive thoroughly.