How To: Lapping Valves on LS Heads At Home

[01ssreda4]

For the most part LS heads are very good quality, you find that most (even higher mileage units) do not require a valve job. If you are swapping on a used set, and want to save some $$$ at the machine shop, here is an alternative for you. I hope this gives you an understanding of valve sealing, and saves you some money.

These heads were taken to a machine shop. They were cleaned and milled lightly but no other work was performed. The bill was around $80.



Here's an intake valve. Notice the silver streak around the lower edge. That's where it seals to the valve seat in the head. We are gonna freshen that surface and hopefully widen it some for a better seal.



Take your compound, and spread it like so. Doesn't have to be perfect.



Stick it into its hole and clamp your drill onto the stem so you can use the drill to spin the valve in the head.



Use the slow speed setting on your drill, and move it in and out (on and off the seat). Wow what a difference 20 seconds makes.



Comparison.



The sealing surface in the head.



Exhaust valve comparison. A little pitting on them is normal and nothing to worry about. Once i mate a valve to a hole, it stays there. I dont move it around once its been ground in. Also make sure you wipe as much of the compound off the head and valve as you can when youre done and hit the valve stem with some wd40 to help it slide in the valve guide easier.



Thats it, repeat the procedure for all 16 valves, makes sure you have a nice even band around each valve and you're good. If one looks off or not even all the way around check the valve and see if its bent slightly. Any questions just ask.

 

[retiredsparky]

Steve, very well done with the pic's. There is no doubt that valve lapping extends valve life and makes the engine more efficient. Thanks for the tutorial!

 

[zraffz]

While I generally won't correct somebody, this should be addressed to prevent others from doing this. I'm not saying he meets the criteria for the following post but this information should be aired out.

Im not the oldest or most experienced guy but I do have a drag racing background and have been building motors as a hobby since I was 17.

Their is a reason you are told to lap valves by hand rather than a drill; if you need to remove that much material for a smooth finish, it requires a valve job. The other issue is you don't get the correct motion with a drill (we will cover this later).

The clearances on the valve seat width is:
Intake .060-.075"
Exhaust .045-.080"

Your seat widths look like they beyond these clearances (again this is speculation but I have been doing this long enough to have a descent idea without a micrometer but that intake valve in the first picture already looks too wide before you lapped it). The issue with this is that you are destroying how the air flows past both the intake and exhaust valve (if you have any doubt that this width hurts air flow have you ever heard how a 5 angle valve makes more power than a 3 angle?) I'd bet you those heads flow significantly worse than factory castings.
Those seats being so wide will spend a very short period of time sealing properly (if they are sealed properly already; another reason you don't use a drill is because the "rolling" back and forth motion in short spurts and frequently pushing downward to break valve/seat contact prevents "lapping lines" that leave grooves around the entire valve seat area; ultimately compromising a proper seal.
Another issue I'd like to point out with the seats that wide is that it is going to encourage heat (which encourages pitting on the exhaust valves).

The other thing I hate is how abrasive that valve lapping compound is. Clean those heads very well to avoid that crap from doing any damage to an assembled motor.

This will in turn negate any gains you are expecting and actually hurt both longevity and performance.


Best of luck with your build.

 

[undy]

In addition, if you've not checked valve guide clearances (a known LS head problem) you'll lack valve-to-seat concentricity with the lapping process. I would expect to see this lapping process in a funny meme on Facebook, nothing derogatory to OP either...

 

[01ssreda4]

I appreciate constructive criticism. Let me first start by saying it doesn't bother me you disagree......but, the pairs of heads Ive done this with I couldn't count on 2 hands and every single one ran fantastic. I wouldn't have posted this otherwise. That being said you can understand why i take internet corrections with a grain of salt. Also, "valve guide clearance is an issue on LS heads" I would wholeheartedly disagree. I have never once had a set of heads in my hand with that issue, or know anyone personally either, I know have A LOT of LS buddies.