Do I need to replace the valve guides when doing a valve job

[sd_iconoclast]

I am taking an automotive machining class and I am finding it impossible to get some straight answers out of our instructor. I am doing a valve job on two sets of 4.3 DOHC heads. I have measured the inside diameter of the valve guides (at top, bottom, and middle) and found them to be well within specs. One set of heads has 100k miles on them and the other set has 150K on them. Should I leave them alone? Should I replace them? Should I knurl them?
I have yet to grind the seats, and I want to get the guides right before moving on.
Can anyone recommend a good book on automotive machining?
I would appreciate any advice from you machinists out there.

[Streetrodder83]

As long as they are within spec. and show no signs of taper, or excessive wear you should be ok. Did you check to see if there was any deflection in the vlave stem. if everything checks out just leave it alone. You are most concerned with the alignment arbor being straigh in the valve guide when you are grinding the seats. Really, this is a matter of preference and budget. Me I would replace them, I like to start with everything new.

[sd_iconoclast]

If I buy new guides, do they come with the correct bore size, or do I have to ream them to fit my valves?
Also, I do not know what you mean by deflection in the valve stem.

[Streetrodder83]

What I mean by deflection is, can you move the valve stem at all from side to side. Usually they are hone to fit.

[sd_iconoclast]

I can move the valves slightly when they are open. Of course they will not move side to side when they are closed. How far should they move (max) at what distance off the seat? My factory manual says to test them at 3mm off the seat, but I cannot find the spec for how far they should move max. The only specification that might be it is the one called "runout" and it is listed as .002". That seems way too little and I cannot get an instrument on the side of the valve at 3mm off the seat.

[Lyle's GTP]

Can you get your hands on a 8mm guide? If so just put it gently into a vice and put the valve into it and wiggle it around a bit. That will be your stock clearance. Now try it on your heads. If there is more than a couple thou. of play, change it. I would avoid changing your guides though. It justs increases the possiblitly of one dropping out, when that happens consider your motor completely fucked. (I've seen this happen to countless motors, it's kind of like a chain reaction to inevitable destruction.) What I would do is (if your original guides are alright). First, ream the top and bottom of the valve guide to give the inside edge a little canfure. Then use a 8mm flex hone and hone them to give nice crosshatch pattern for better oil retention. Then you should be fine. By the way I've done the valve guides on 4-5 of these motors and have never had to change a guide, so you will probably be alright.

Lyle