Valve lapping question

[gregaba]

Reading on some of the engine building sites [Ford Muscle-engine labs etc] and have found some of these builders say not to lap the valves.
I have all ways lapped in my valves.
Does anyone have a good solid reason for not lapping in the valve's?
Greg

[GerryP]

It's because the cutting and grinding machines do a much better job with valve and seat dimensions and lapping isn't necessary.  I'm not sure that it hurts, though.  Some say introducing fine abrasives into the mix is a failure point that doesn't need to be there.  I guess if you really trust the machine work, it becomes unnecessary.  I'm surprised you could find articles taking the position of not doing -a change from best practice- it but they don't explain why.  I still have my cups and lapping compound.

[blykins]

I do. 

For one, after a valve job, it's a good way of seeing the contact margin on the valve and seat so that you know what's going on.   I even lap the valves in on head/valve packages that I receive in from other companies, such as TFS, AFR, etc. 

I know a couple of the head porters I work with always mark/etch the valves from what seat they came out of. 

[Joe-JDC]

It depends on the valve job.  If you use a 46* seat and 45* valve angle, then just ping the valves to see if they fit.  Same for other valve angles if one is different from the valve face then just simply tap/ping the valve against the seat and you are good to go.  The interference angles are very common in current valve jobs.   Joe-JDC

[gregaba]

I guess if you trust machines not lapping would be ok.
I asked brcause I bought a nice set of heads and had to replace some valves.
I gave all the valves a 30 second lap and then filled the heads with liquid and let them sit for a couple of days.
Even though the valves looked good I still had 3 of the old valves seep out some liquid.
I have all ways keep my valves in the same hole they came out of as taught to me by my dad in the 60's when I first started working on engines.
As to the compound in the heads I have a heated solvent washer that really does a great job cleaning parts, more the likely banned by the epa now.
Any way i just needed to know about this new theory.
Greg

[Falcon67]

I swipe of Blue Dykem on a Q-Tip and a little grinding compound gives a good indication of contact patch.  Can't hurt, that's for sure. 

[Barry_R]

I will lap them every so often - especially if I am looking for something or suspect an issue.  I do not believe that it hurts anything as long as you clean up after.  On new work I will usually just check contact by painting the valve & seat with a Sharpie & giving them a spin....

[wowens]

I lap em, then spray the seats with brake cleaner through the straw one at a time and immediately blow dry with high pressure air. Same with valves. Then the normal cleaning process before assy.