Okay, you’ve already cut or ground your valve seats to the correct angles; you’ve ground the valve face in your valve refacer. Are you ready for final assembly of the cylinder head? Maybe, maybe not. The next step in many cases is to lap the valve to the valve seat for a final, perfect fit.
Contact us to discuss your requirements of Globe Valve Lapping. Our experienced sales team can help you identify the options that best suit your needs.
Lapping has been around for as long as engine building has been around. It’s a very simple, straightforward procedure.
All lapping tools work in the same manner. This means the tool is attached to the valve head, lapping compound is applied to the valve seat or the valve face and the tool is rotated left and right to lap the valve to the seat. It’s kind of like trying to start a campfire by spinning a stick fast enough to create enough heat to ignite your kindling. Of course, with valve lapping you’re not going to even try to start a fire, but the motion is the similar.
First, select the type of lapping tool you prefer. Goodson offers a variety of types and sizes including:
Let’s take a look at each of them.
The traditional and extra-large lapping sticks are operated entirely by hand. They include a suction cup on one or both ends that you’ll use to attach it to the valve head. Sometimes a little spit will help to keep the suction cup attached. Of course, it’s always best to make sure all oils have been removed from the valve surface to ensure the suction cup mates to the valve. Suction cups are available in a variety of sizes to fit a range of valve heads.
Another type of valve lapping tool incorporates a pump to create vacuum to ensure the tool stays attached to the valve head. Don’t play with these unless you want to give yourself one heck of a hickie. They generate a lot of vacuum!
If you’re looking for a powered lapping tool, you’re in luck. Goodson offers two of them. First is the Powered Lapping Tool that you drive with a power drill. The tool is designed to change the rotary action into an effective oscillating motion.
Last, but not least is the top shelf unit that most NHRA Top Fuel teams (and other race teams) use. The Air Powered Valve Lapping Tool. This heavy duty unit operates on 90 PSI of shop air and makes quick work of valve lapping.
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The only thing left to talk about is Lapping Compound – a silicon-carbide, grease-based paste.
Selecting the correct lapping compound is generally a matter of personal taste. Goodson offers several grits; from 120 to 1200 so you have lots to choose from. If you’re just getting started, you may want to experiment with different grits until you find what works best for you.
There are pros and cons to valve lapping and over time, you’ll find out which applications need to be lapped and which ones don’t. Practice makes perfect, but keep one thing in mind:
Lapping is a finishing step and should NOT be used to correct a bad seat, or worse yet, a valve that is improperly ground.
As always, if you have any questions about Valve Lapping or any other engine building topic, contact the Goodson Tech Services Department at 1-800-533-8010.
Valve Seat Reconditioning
This job is best left to your dealer or local
machine shop. They have the special equip-
ment and knowledge for this exacting job. You
can still save considerable money by removing
the cylinder head and taking just the head to
the shop. The following procedure is provided
in the event that you are not near a dealer and
the local machine shop is not familiar with the
seat reconditioning specifications.
1. With a 15° valve seat cutter, remove just
enough metal to make bottom of seat concen-
tric. See Figure 77.
2. With a 75" valve seat cutter, remove just
enough metal from top of seat to make it
concentric.
3. With a 45° valve seat cutter, cut a seat that is
1.0-1.2 mm (0.039-0.047 in.) wide.
I can't speak to the specifics of your particular engine without the service manual in front of me.That little bit of surface pitting that you had on the valve face is pretty normal, and it may have been seating just fine. The best test is to squirt some carb cleaner into the port with the valve installed, and see if any leaks past the valve.Having a wide contact area between valve and seat can actually cause that pitting that you saw. The exhaust valve runs VERY hot, and the hot valve hits the seat and transfers heat when in contact with it. If the contact patch is too big, it can cause the seat to get hot enough to cause micro-welds to the valve, and that is what causes the pitting.I sometimes forget that on this forum, we are not always talking about modern engines. Modern engine design has hardened valve seats, and they are ground to three angles. The multiangle valve job allows better flow through the port because it makes a more rounded path for the gasses to flow past.Some motorcycle heads and valves do not tolerate regrinding, because there ain't enough meat there. I am a little more used to Harley engines. They have automotive type valves that can be reground, and the seats can be reground or replaced. The 3-angle valve job is de rigueur.Here is what the service manual for my '81 Suzuki GS450 says about reconditioning the valve seats.Now, a word about valve grinding compound.The smallest traces of it in your engine is highly destructive. It doesn't just float around and eventually find its way to the oil filter or get drained out in an oil change. It embeds into engine parts and stays there to cause wear forever. After you are done lapping the valves, be totally anal/compulsive about cleaning them. Use hot water and detergent. Valve grinding compound is water borne, so don't try to clean it out with things like carb cleaner, use water and detergent. Get in there with soapy brushes and be VERY thorough.
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