just curious......I always thought a valve job was getting the valve seats and head precision ground at a machine shop so they mate nicely so as to not lose compression.

However, recently someone was telling me you can use lapping compound, put it on the valve seats and then (after removing the springs etc) turn the valve (in its place in the head) with an electric drill. Has anyone ever heard of this. Will this actually do an effective job???

thoughts, comments????

 

Yes you can lap the valves if they are in good shape along with the seats. Infact you are supposed to lap the valves before you install the heads anyway to insure good valve seal.

 

lapping is more of a finishing operation, it doesn't replace valve grinding

 

A good vavle job should consist of a few things. working at a machine shop, I do this crap daily.

First- The heads should be degreased and magnafluxed. Heads from F-bodys are cracked more often then yor average car head since they get beat.

The valves should be checked for stem wear and replace as neccasary. The valves should be ground- only if there is enough vlavle left to grind

The guides should be knurled, or replaced if neccesary. Again heads from a sports car are more prone to wear in this area.

The springs should be tested, and are ussually weak from high rpm.

the seats should be ground, and replaced if sunk, or chewed up

the locks/retainers need to be evalulated. Locks take a fair beating.

The head should be surfaced as well.

the springs should be shimmed back to the correct installed height on a SBC 1.700 inches.

Lapping the valves is a process I don't reccomend. Its only good for a finish.

If your valves are not sealing or your burning oil YOu need to consult a professional. Joe

 

so I am assuming then that if the cylinders varied in compression (and it was due to valves not sealing perfectly) that this lapping would not really do much of anything and not improve the compressio at all???

Do you mean where the spring sits or where the valve meets the head?

 

always replace the valve guide if worn. no need to knurl them just replace them. if it worn it's worn.