How to Assemble Cylinder Heads

February, 2009

Cylinder heads have long been recognized as a critical component of horsepower, and today we're fortunate to have a vast selection of OE and aftermarket offerings to choose from. However, while many aftermarket heads come as complete assemblies ready to bolt to your engine, there are still many manufacturers that sell bare castings, requiring the end user to procure and assemble the necessary parts and pieces to create functional heads. Some manufacturers offer bare castings as an alternative for consumers who want to create a custom valvetrain, but in some instances, a particular head may only be available as a bare casting.

Whatever the case, there are a number of factors to consider when purchasing and assembling bare cylinder heads. We encountered this recently when we obtained a set of bare iron castings from Pro Topline to test. The iron heads have nice big ports, modern combustion chambers, and are machined for big valves, but we still had needed hardware to get them together. Fortunately, Powerhouse in Bakersfield, California, offers complete valve kits specifically for these heads, as they carry Pro Topline products. We took everything to JMS Racing Engines in Monrovia, California, to get professional input on the process of getting our heads together.

Merging valves and head castings... read full caption Merging valves and head castings from different sources can be tricky business, as the relationship between the two is intimate, leaving little margin for error. The first fitment issue to check is the valveguides. This is a precise fit, which has to be correct to avoid either excessive oil burning (too loose) or damage to the guides (too tight). For typical pushrod-type cylinder heads, JMS likes to see 0.001-0.0015-inch clearance for the intakes and 0.0015-0.0020-inch for the exhausts. Experienced cylinder-head guys like JMS's Oscar Alvarez can simply feel when it's right. Without any oil, you should be able to wiggle the valve just slightly in the guide with the head of the valve about a half-inch off the seat. Any binding is an indication of a fit that's too tight, requiring the guides to be reamed slightly. Our Powerhouse valves fit just right in the Pro Topline heads.	If the bare heads are shipped... read full caption If the bare heads are shipped with a finished valveseat, as is the case with these Pro Topline castings, the next step is to trial-fit the valves to the seats to see how they mate. Mike Johnson of JMS showed us a good trick to illustrate the contact between the valve and seat. First, he uses a marking pen intended for a dry-erase board to coat the seating surface of the valve with ink.	Next, the valve is inserted... read full caption Next, the valve is inserted in the corresponding valveguide and then seated with a swift jab of the hand so the contact point between the valve and seat leaves a ring of bare metal in the pen ink. The valve can also be gently twisted against the seat to create the witness mark in the ink, but twisting too hard can mask problem areas.
This is what you should wind... read full caption This is what you should wind up with: A nice clear ring in the ink, indicating a positive seal around the perimeter of the valve seat. The ring should fall somewhere in the middle of the seating surface of the valve, preferably toward the outer edge. Our ring was slightly toward the inside, which is still acceptable. If the sealing ring falls right at the inner edge or partially off of the outer edge of the valve, further machining is necessary.	The fitment we found between... read full caption The fitment we found between our valves and seats was nearly perfect, which would allow us to assemble the heads, but JMS recommended that we take some extra time to lap the valves to the seats. This process isn't considered mandatory, but does provide added assurance that the valves are sealing to the seats when closed. The first step is to coat the seats with blue machinist's layout die.	Next, Alvarez dabs a little... read full caption Next, Alvarez dabs a little valve-grinding compound on the seat of the valve. He normally uses two grades of compound, starting with fine and only moving to coarse if the fine grade fails to establish a clear seat. Even when coarse grade is necessary, Alvarez finishes with fine.
With the fine compound on... read full caption With the fine compound on the valve, the valve is set in the guide, seated, and then a suction cup handle is stuck to the face. The handle is rolled back and forth quickly while slight downward pressure is applied. After a couple seconds of turning the valve back and forth in one spot, it is rotated and the process is repeated.	Every few seconds, the valve... read full caption Every few seconds, the valve is pulled from the guide and checked. The goal is to establish a consistent gray band around the valve, indicating where the seat actually is. The gray band will fall in the same place as the ring previously made in the pen ink, though the distinct gray indicates a positive mating, and therefore sealing, between the valve and seat.	The gray band should be even... read full caption The gray band should be even more distinct on the valve seat in the head, thanks to the blue die. Like the seat on the valve, the gray band should fall right around the middle of the seat. With multi-angle valve jobs, as shown here, it is particularly important to verify where the valve is actually seating, as the width of the center 45-degree angle cut of the seat is usually fairly narrow as a result of the surrounding angle cuts. Our valves lapped in with minimal effort using fine compound.

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