Budget Rebuilding Street Cylinder Heads

We started this rebuild with a basic set of iron 318 castings, but the process is the same for virtually any cylinder head, regardless of whose name is embossed on the valve cover.

We started this rebuild with a basic set of iron 318 castings, but the process is the same

Car crafting is all about power-enough to run 12s in the quarter-mile and spin the tires at will. But not everybody can afford a shiny new set of aftermarket aluminum cylinder heads. The next best thing if you can't afford a trick set of alloy castings is to lay a little TLC on the heads you have. Last month, we introduced you to Steve Strope and his stepson Seth's '66 Mopar Coronet. While the resurrection bodywork continues on that somewhat abused B-Body, the pair also opened up the 318 Mopar engine that will eventually find its way into the engine compartment. The Coronet's original powerplant was an ancient polyspherical 318 that only the most diehard Mopar fan could learn to love. Instead, the pair chose a '70 LA version that promised to be in better shape. At first, the Strope plan was to perform a quickie Krylon rebuild by just cleaning and painting the low-mileage donor motor while adding an intake and a cam. That's when the, "Well, as long as we've got it apart" song started. Before the final note had played out, the heads fell off in anticipation of a quick valve job. We took the heads to Jim Grubbs Motorsports where ace machinist Ryan Peart transformed the greasy leakers into like-new castings.

Most guys don't have machine shops in their garages, so the focus of this exercise is to point out areas where a couple of simple and inexpensive machining steps can improve airflow for cheap and to illustrate just what goes into a quality rebuild on even stock iron cylinder heads. Check it out.

Guide Rebuilding
The biggest issue with used cylinder heads is valve stem and guide wear. Generally, used heads will have loose guides that allow the valves to move laterally relative to the valve seat. This movement tends to beat up the seats, deteriorating their condition, which also diminishes the seal under cylinder pressure. If this isn't bad enough, loose guides allow the valves more room to move around, which trashes the valveguide seals. From this short description, it should be clear that a set of properly installed and clearanced valveguides is essential in the build process. So that's where we will start.

After disassembling the heads, the first thing Peart did was degrease the castings. These are 2843675 castings with 1.78/1.50-inch valves that use rocker shafts instead of individual studs. The center two exhaust ports are siamesed and employ an odd dogleg design that can best be described as weak. The intake ports measure a small 119 cc, while the chamber measures 68 cc.
After disassembling the heads, the first thing Peart did was degrease the castings. These
To accurately establish valveguide clearance, Peart first measured the existing valves and then used that spec to establish a guide for a dial bore gauge. The original valves were in surprisingly good shape, so we decided to reuse them. The clearance turned out to be 0.004 inch on the intake and 0.006 inch on the exhaust. This demanded new guides.
To accurately establish valveguide clearance, Peart first measured the existing valves and
The first step in rebuilding the guides is to ream the original cast-iron guides to make way for the replacement inserts. This is a critical step, since the guide should be maintained perpendicular to the seat as much as possible.
The first step in rebuilding the guides is to ream the original cast-iron guides to make w

As an option, it is possible to purchase stock replacement valves with oversized stems that are designed to compensate for guide wear and bypass the guide work. This is an option you might consider, especially if you have to replace the valves due to excessive stem wear.
As an option, it is possible to purchase stock replacement valves with oversized stems tha
While entire replacement guides can be used, bronze wall guide inserts retain cylinder head integrity yet produce an excellent foundation. These bronze K-Line guide liners also improve lubricity, allowing a tighter valve stem clearance that improves durability.
While entire replacement guides can be used, bronze wall guide inserts retain cylinder hea
The guides are chosen in an attempt to create as close to the desired inside diameter as possible. Pressing them in from the bottom collapses the opening in the guide, creating a slightly undersized inside diameter.
The guides are chosen in an attempt to create as close to the desired inside diameter as p

With all the guides in place, Peart pressed a broach through the guide from the top to bond the guide to the head, which improves heat transfer characteristics.
With all the guides in place, Peart pressed a broach through the guide from the top to bon
Peart then passed a hone through each guide to establish the ideal inside diameter. This is somewhat time consuming since it requires quite a bit of honing and then measuring. This is one area where the money you pay for good machining pays off.
Peart then passed a hone through each guide to establish the ideal inside diameter. This i
The last step with the guides is to spot-face the top of the guide to eliminate a sharp edge caused by the broach. Note the spiral oil path that improves lubrication, keeping the valves cooler.
The last step with the guides is to spot-face the top of the guide to eliminate a sharp ed

Valve Grinding

Besides guide wear, it's also a good idea to check the valve face margin. The margin (arrow) is the portion of the valve between the face and the outside diameter of the sealing face. A wide margin is essential especially for exhaust valves. Valve margins often become very thin if subjected to excessive valve face grinding. A thin exhaust valve margin not only decreases flow but can also overheat, which can contribute to detonation or pre-ignition problems.
Besides guide wear, it's also a good idea to check the valve face margin. The margin (arro
Since valve stem wear on the OE valves was acceptable, Peart first subjected them to a quick stem honing to ensure a square surface from which to work.
Since valve stem wear on the OE valves was acceptable, Peart first subjected them to a qui
Virtually all performance valve jobs use a 45-degree angle on the valve. Some Pontiacs did experiment with 30-degree seats, which improves low-lift flow but at the cost of flow at higher valve lifts. The key to grinding the valves is to remove as little material as possible to establish a concentric sealing surface.
Virtually all performance valve jobs use a 45-degree angle on the valve. Some Pontiacs did

We elected to reuse the stock valves to save a little cash (that Coronet is gonna need a lot of bodywork). However, we did try a simple 30-degree back-cut (arrow) on the intake valve to see if that would help the flow. This additional angle generally helps low- and mid-lift flow. It's a simple trick that your machinist can perform during the valve-grinding step.
We elected to reuse the stock valves to save a little cash (that Coronet is gonna need a l
The advantage of a performance aftermarket valve like a Manley, for example (left), is not just in the stainless material. Most factory valves employ a sharp radius from the stem to the valve seat. Worse yet, many exhibit a ditch or undercut directly behind the seat that decreases flow. Depending on the application, new performance valves are only slightly more expensive than stock replacement pieces. Note the swirl polish and gentle radius from the stem to the seat in the aftermarket valve on the left.
The advantage of a performance aftermarket valve like a Manley, for example (left), is not

Seat Work
In ancient times (about 20 years ago), seat preparation was performed using a series of grinding stones to establish the seat angles. Generally, this involved three stones that were dressed at the specific angle required. The accepted standard valve seat for a typical performance intake and exhaust valve seat uses 30-, 45-, and 60-degree angles. The 45-degree seat matches the angle ground on the valve. The 60-degree angle is also often referred to the throat angle that directs the air (on the intake side) from the port toward the seat. Then the 30-degree top angle helps radius the flow into the chamber. Different cylinder heads can and do respond to different combinations of angles, but the classic 30-45-60 is tough to beat.

With the advent of the dedicated valve-cutting tool machines such as the Serdi, Sunnen, and others, the machinist can specify a custom-made cutter that machines all three seat angles and widths simultaneously. Not only is this faster and far more consistent through all 16 valve seats, but it also ensures far more seat concentricity, which also helps flow.

This is the stock chamber after cleaning. You can see that if there are three angles on the intake seat, they are very thin. Oddly, before and after flow testing revealed that we did not improve airflow even with a performance-oriented valve job.
This is the stock chamber after cleaning. You can see that if there are three angles on th
Peart set up the heads in JGM's Sunnen SGM-1500 machine and efficiently cut all the intake and exhaust seat angles using a specific cutter for each of the two different seats. In this case, JGM chose a slightly different 38-degree top cut along with the standard 45-degree seat, followed by a radius in the throat as opposed to the typical 60-degree angle.
Peart set up the heads in JGM's Sunnen SGM-1500 machine and efficiently cut all the intake
This photo illustrates the three angles on the intake and exhaust valve seats. A very minor amount of grinding just beneath the throat cut would help the flow. The stock throat diameter on this Mopar exhaust port measures almost 85 percent of the valve diameter (1.270 versus 1.500). The rule of thumb is the throat diameter should not exceed 88 percent for the exhaust, which in this case means there is very little room for modification. On the intake side, the recommended percentage is a maximum of 90 percent. This Mopar intake measured 1.48 inches, which calcs out to 83 percent on a 1.78-inch valve.
This photo illustrates the three angles on the intake and exhaust valve seats. A very mino

Head Assembly
With the machining complete, all that's left to do is assemble the heads. We went with an Edelbrock valvespring to match the camshaft, since the springs were really inexpensive. There are a couple more steps that include choosing the right valveguide seals and valvesprings and ensuring that we have plenty of clearance for our new cam. The cam is a mild Edelbrock Performer-Plus with only 0.420-inch valve lift, so coil bind and retainer-to-seal clearance aren't issues. We also upgraded the intake seals to Viton-style positive seals that mount on the outside of the guide. Once the spring clearances were verified, Peart assembled the heads with a little lube on the stems, and we carried them back to Strope's shop to bolt them on the engine.

While the cam we decided to use in the 318 is very mild, it doesn't hurt to check for installed height, which is the distance from the spring seat to the bottom side of the retainer. As you can see, with a 0.030-inch-thick spacer, the height measures 1.630 inches. The spec is 1.650, so we're slightly tighter, which should bump up the seat pressure to around 95 pounds.
While the cam we decided to use in the 318 is very mild, it doesn't hurt to check for inst
There are several types of valve seals. We decided to use a positive-style seal (left) instead of an umbrella seal (middle) that was on the heads. Another style of umbrella is the hard-plastic style (right). On the exhaust side, we used new O-rings that are placed on the valve in a groove just under the retainer. This directs a little more oil to the exhaust side.
There are several types of valve seals. We decided to use a positive-style seal (left) ins
Here is the finished head with the springs installed and ready to be painted Mopar orange and bolted back on the engine.
Here is the finished head with the springs installed and ready to be painted Mopar orange

CLEARANCES
COMPONENT	CLEARANCE (INCHES)
Valve stem to guide	Intake, 0.001 Exhaust, 0.0015
Valve seal to retainer	0.050
Coil bind	0.050
Installed height	1.650

MACHINE COSTS
OPERATION	COST
Clean and Magnaflux	$88.00
Install new guides	170.00
Back-cut valves (8)	32.00
Surface heads	56.00

These are JGM prices that may not be typical of other machine shop prices, but they will give you an idea of what the operations cost.

FLOW TESTING
VALVE	STOCK	VALVE JOB	BACK-CUT	CHANGE	INTAKE	CFM	(PERCENT)
LIFT	INTAKE	EXHAUST	INTAKE	EXHAUST	INTAKE	CFM	(PERCENT)
0.100	52	54	54	47	55	1	2%
0.200	108	97	107	90	118	11	10%
0.300	157	119	156	116	163	7	4%
0.400	172	128	177	126	164	-7	- 4%
0.500	166	135	167	132	168	1	0.5%

Note that our new valve job really didn't improve the flow, which is not unusual. The change that really helped was the 30-degree back-cut to the intake valve. Note how this improved the flow at 0.200-inch valve lift the most and then fell off, actually hurting flow slightly at 0.400 inch. Since our cam's max lift is only 0.420 inch, this should be worth a little torque if nothing else.

SOURCES
Edelbrock 2700 California St. Torrance CA 90503 310-781-2222 www.edelbrock.com	Jim Grubbs Motorsports 28130 Avenue Crocker # 331 Valencia CA 91355 661-257-0101