This valve is from my LS1 (Exhaust #3). It's suffered from a lot of carbon build-up due to a history of fueling/spark problems.

I've tried cooking it in ethylene glycol. I've tried using abrasion with a drill-mounted brass wheel brush, and it hasn't improved the situation much.

Can I just start lapping this valve by hand or would that damage the valve seat?

Valve Face 1

Valve Face 2

Valve Face 3

Valve Face 4

Valve Face 5

  • have you tried media blasting it? something like walnut shells should work pretty good.
    – Ben
    Commented Mar 29, 2017 at 13:38

1 Answer 1


Do not try to lap this (or any of your valves which may look like this) without getting them cleaned up first. You must know carbon is a very tough substance (remember what diamonds are made of, right??). Given that, if you tried to start lapping this you will cause some major scoring on both the valve lip and the seat. It will be just plain ugly.

I'd highly suggest you do what Jafromobile showed to do in this video. For the uninitiated, he suggests you get a brass wire wheel on a grinder, then put masking tape on the stem of the valve, secure the valve stem in a drill, then using both the rotation of the drill and the wire wheel, clean the heck out of them. The dual action of both the valve spinning and the brass wire wheel should do the trick, as well as prevent a single area from getting hammered too much. Here's a still as he works from the side to clean the backside of the valve.

enter image description here

I realize the carbon is going to be a bit tough, but if you want to reuse the valves, you'll have to get these clean before you can lap them and hope they'll seal.

  • Update: I let the valve soak in fuel injector for a couple of days, then revisited it with a brass wire wheel mounted on a cordless drill. It's starting to clean up nicely. Also, there's no way a valve lapping handle would stay suctioned to the bottom of the valve without removing all of the carbon first.
    – Zaid
    Commented Apr 3, 2017 at 2:46
  • @Zaid - Good point about the lapping handle! Still, people find crazy ways of making things work. The point here is, you need a clean valve from the get-go. Without the clean valve, you won't get clean air flow. Get it cleaned up before you even start reconditioning. Commented Apr 3, 2017 at 13:34
  • Carbon is actually very soft and porous. It takes extreme heat and pressure to turn carbon into diamonds (nothing that a car engine can even hope to touch). Pencil lead is also made or carbon. That said, I have used lapping compound to clean carbon from seats on lawn and garden equipment. The specific one that comes to mind is a Honda lawnmower. This was over 10 years ago, still use it to this day. Originally was going to do a full valve job but the kit did not support valves that small.
    – vini_i
    Commented Sep 19, 2017 at 13:53

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