Learning Curve - Understanding the Evolution of Cylinder Head Seat and Guide Machines - Engine Builder Magazine

Learning Curve – Understanding the Evolution of Cylinder Head Seat and Guide Machines

Like many of you, I’ve been watching the transition in head machines for the engine machinist industry with great interest. And you and I both are looking at how changes in equipment will impact your business.

You see, I teach in an engine machinist program and when I took over the program in 1993 our teaching shop was set up great for a shop right out of the ’70s. Today, our students need to know about machines capable of working in the future!

Before coming to Northwest Technical College to teach I had owned a shop. Looking back now, I realize just how unaware I was of the quality of work I was producing. I just didn’t know any better – I was just trying to get by.

Boy, have things changed! Do you remember the many generations of three-angle seat cutters and what we used to get by with? Grinding seats is still needed, but just 10 years ago we were grinding 80 percent of the seats. Though we still grind when necessary, today we cut 90 percent of the seats in the heads. In addition, we also need a good indicator for measuring valve seat runout after we cut the seats. Yes, we use a vacuum tester, but we still need to know what we are cutting for runout when machining seats.

We just purchased a new head machine this year for the college. Though I have always been worried about getting into carbide pilots, now I would never go back to high-speed steel pilots. Everything is just so much easier to machine when using carbide pilots.

As for the machines themselves, each has some features and benefits; it just depends on your price point and what you can afford. You might have to consider the Chevrolet not the Cadillac, but you might be able to get the previously owned Cadillac. There are a lot of great machines out there that have plenty of life left in them, but you need to test drive them before you commit to the quality of the ride.

A valve seat and guide machine is an essential piece of equipment for any shop that does cylinder head work. Of course, there are a number of important factors to consider as you make your decision.

Equipment suppliers and users alike say the machine’s versatility is very important. What are the capabilities of the machine? Can it handle longer or wider cylinder heads? Does the machine have enough vertical travel and fore and aft travel to do what you want it to do? Is a dedicated valve guide and seat machine all you need for head work or would a multi-purpose machining center provide additional capabilities that would better serve your needs?

Most of the newer machines have a floating head that makes head repositioning fast and easy. A tilting head allows you to align the spindle with the guide in the cylinder head rather than having to align the head to the spindle. An older used machine with a fixed head can’t provide that kind of versatility. It’s the same story for the fixturing. Can the fixturing handle the kind of heads that you work on most? If not, what will it cost to replace or upgrade the fixturing so it can handle such heads?

Guide and seat machines have evolved over the years. Constant refinements have been made to improve speed, accuracy, flexibility, ease of setup and operation. Some of the newer machines are available with digital or computer numeric controls (CNC). Maybe you don’t think you need such bells and whistles on a valve guide and seat machine. But once you make the transition from manual equipment to digital or automated equipment, there’s no going back.

Ten years ago I was teaching my students that they needed to be producing a dollar per minute of work, $60 per hour, today we need to be over $120 per hour. If not we cannot even consider the purchase of a new machine and to pay the employees who run it.  If we do not have the volume to keep your investment busy you have to make the hard decision to keep doing it the same old way and try to pick up the quality that is required to be competitive in today’s engine machinist industry to increase your bottom line.

So the question is, what will make a difference in the kind of head machine you consider? Are you doing heavy-duty work, or doing smaller heads with less than one inch valves? If you are doing the latter, you will need to consider the small three-angle seat cutter system. In a performance engine shop you might spend upwards of $125,000 to get the quality you need to compete in your market. I know of a NHRA shop that has two different head machines, one for doing canted valves and the other one for doing in-line heads. I know most shops can’t consider two head machines, but it depends on the quality and the volume of heads you are running through your operation.

So what is the right head machine for you? Well. . .  I don’t know. I do know that quality matters, carbide pilots are a must have and have enough of them. I do know a lot of older machines cannot hold the tolerances that are required to work on today’s heads. Did I say quality matters?

I know of a dirt track shop that uses a CNC touch screen head machine that sells for over $125K, and what a great job that machine can do. I know of another shop that has two self-leveling head machines and one new style manual leveling machine, both are great machines but each has features and benefits that may or may not fit your needs.

Several years ago, I purchased a gauge to check valve run out when grinding valves. WOW! I can measure in tenths! I have another gauge, that if I look real hard, I can pick out .005˝ runout on a valve. What a mistake to purchase the wrong runout gauge. This changed everything on the valve refacers I use. Now I am finding more uses for the better runout gauge. I have found some of the high-speed steel pilots for the head machines to have .010˝ bend in them, which is another reason I like my new carbide pilots. I found some expandable pilots we use for grinding seats to be bent as much as .020˝.


Accuracy is absolutely essential regardless of the brand, other features or age of the equipment. Valve seat to guide concentricity is the number one criteria for any valve guide and seat machine. Many factors can affect concentricity and accuracy. Most experts recommend using dead pilots (fixed pilots) rather than live pilots. Live pilots leave room between the pilot shaft and the inside diameter of the valve guide so they can spin freely. Even if that is only .0001˝, it still adds up to .0001˝ on each side of the shaft. Depending on the length and size of the pilot, that may allow as much as .001˝ of tolerance runout at the valve seat.

Too much runout in the seat will cause a valve to flex every time it closes, and over time this can lead to valve fatigue and possible valve failure. The most accurate method for making sure the valve seat is concentric with the guide is to use a concentricity gauge. A simple vacuum check can be misleading because a valve can still seat even if the seat is slightly off-center with respect to the centerline of the guide.

Fixed pilots have a gradual taper that centers off the middle of the valve guide (which is important when you are working on heads with high mileage valve guides that are typically worn at the top and bottom). The other benefit of fixed pilots is that you don’t have to have as many sizes, so your investment in pilots can be 30% lower than if you were using a live pilot system. Whether you choose to use fixed or live pilots, you should always use carbide pilots.

Other factors that affect accuracy include the type of seat material you are cutting, the rpms of the machine and the sharpness of your cutter blades. Seat concentricity can also be affected by how the spindle is driven. Some machines have belts that connect the main spindle quill to a motor in the back of the machine. This may cause vibration which translates into runout that affects the concentricity of the valve seats.

For machines that do have the motor mounted directly on the quill, it is important to have adequate power since torque affects performance. If a machine lacks sufficient power to cut a seat properly, you get chatter. Always look at the type of motor (bearing motors vs. servo-motors that have higher vibration frequency), and compare the power rating of the motor.

Probably one of the most overlooked aspects of achieving the best valve seat concentricity is leveling. Many people are using bubble levels, or simple 1-axis digital levels. The problem with the bubble level is that there is no way to get the accuracy needed. With a simple 1-axis level, the reading is not taken at the spindle quill but from a post on the side of the machine. To align the post to the quill, you must put an adapter in the quill, test it, then test the post.

But there’s no guarantee the alignment will remain the same. If you accidentally hit the post too hard, or didn’t tighten it down enough, you can move your “0” on the level. As a result, your post will not be aligned properly with the quill. If you then level your valve guide to the “0” on the post, the valve guide and spindle quill will not be aligned. The most accurate approach is to consistently check the location of the quill directly so you know it is lined up with the valve guide.

The rigidity of the machine is also important. The more rigid the equipment, the better it can hold accurate alignment and resist vibration. Consider the strength of the base casting, column and head stands. Can it withstand an earthquake or will it quiver and shake with every tremor?

Something else you may not know is that valve guide and seat machines built for the U.S. market are not the same as those that are built for the European market. In Europe all of the guides and seats are replaceable so the only machining operation is to profile the seats and occasionally counterbore for oversize seats.

In the U.S., we do the same kind of jobs but also reclaim spring pockets, drill for replacement guides, drill out broken studs and re-thread the holes, counterbore the castings for seat inserts, replace spark-plug threads, drill for screw-in studs and guide plates, and then profile the seats to perfect geometry as well. So the machine has to have the power and versatility to handle all of these jobs well.


Speed is important, but not at the cost of accuracy. Since dead pilot systems are capable of producing higher tolerances, using a dead pilot system is preferable to a live pilot system even if it is somewhat slower. There are new tools on machines like “spring-less ball heads” that allow the worker to move from one guide to the next without having to pull off all the previous tooling. It makes the work faster and easier on the operator without sacrificing accuracy.

Of course, the most accurate valve guide and seat machine in the world won’t do much to boost your productivity and profitability if it is a pain to set up and use. That’s why equipment suppliers have continued to refine and improve the setup and operation of their machines so they are quick and easy to use. Mounting a cylinder head in a cradle is fairly simple on most machines today.

Automated digital or CNC controls now make it possible for almost anybody to operate a valve guide and seat machine. With a manual machine, the operator has to mechanically move the quill down. No matter how good the machinist is, it is nearly impossible to be absolutely consistent with every repetition that they do. On top of that, some machinists are more skilled than others. You have good, better and best employees. With an automated valve guide and seat machine, the variability and inconsistencies between employees is eliminated. You get consistent high-quality results no matter who is operating the machine.

In my position as an instructor, I feel I have the responsibility to educate without favoring one brand over another. Each has features and benefits that other machines may not have so you need to consider what your needs are. It takes being a professional businessperson to know how to make your shop profitable and to keep quality employees to get the job done with the ever-changing standards that are expected in our field of expertise.  As you consider purchasing a head machine just remember that a machine that works for one type of application may not work best for the type of heads you are working on, talk to people and look for the best machine for the work you are doing. If you want to know how good a machine really is or what kind of customer service you can expect when the need arises, talk to someone who is using similar equipment. Your equipment salesman should be able to provide you with some reference contacts in your area you can call for more details. Do call them and ask them if they are satisfied with their equipment, if they have run into any problems with it, and if so how the equipment company handled it. A red flag before the sale is better than an unpleasant surprise after a sale.

Other Considerations

A list of other things you should consider when looking at valve guide and seat machines includes the following:

Tooling: Is there adequate onboard tool storage? What are the tooling capabilities of the machine? How easy is it to change the tooling? Is there an onboard sharpener to restore the cutting edges?

Ease of Use: Changing tooling aside, how quickly can you set up and cut a seat? Ease and accuracy of leveling the machine? If the machine has an airfloat machine work head, it can provide ease of floating and locking.

Convenience: A vacuum for keeping work area clean, extensive front-to-back and side-to-side travel of the work head and adequate work lighting (this one can’t be stressed enough!) will make it easier to get the job done.

Accuracy: Can the cutting head tilt +/- 15 degrees for canted valve guide work? Is there a built-in vacuum tester (To test your work before you take it off the machine)?

Motor: Is the motor power, motor type, motor location and RPM variation adequate for your shop’s needs.

With a lot of technical information to consider, you may have noticed that “price” isn’t on the list. That’s because the cost of the equipment should be the LAST thing you look at when choosing a new piece of equipment. Don’t let the high cost of some machines scare you off. Yes, everybody has to operate within a budget, and no piece of equipment is worth the price if it can’t pay for itself one way or another. However, we need to make sure we are doing quality work and to measure what we are doing. Your investment should deliver a higher level of quality, allow you to work on a wider variety of heads or to do jobs your current machine can’t do, and it should give you a measurable improvement in productivity and profitability.

The price of the equipment doesn’t always reflect the true capabilities of the equipment, but as a rule you should expect to pay more for digital or CNC controls, additional features and tooling. Many equipment suppliers offer a variety of models and options, and can often customize a machine to match your specific requirements and finances. Communication is important here to make sure that what you are buying is what you actually need and that you fully understand the capabilities of the equipment.

So, I hope this will get you thinking of the quality of the work you are doing. This is the bottom line, if you have out dated equipment that cannot cut a seat correctly you must consider upgrading your head machine to improve productively and prevent warranty situations.

The students coming out of my program (and the other quality programs across the country) will expect nothing less from their future employers. n

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