Instruction Manual for Installation of 4-Valve® Heads on Harley-Davidson EVO Engines


Congratulations, you have purchased a piece of 21st century technology for your Harley-Davidson! This is precision-made equipment that requires unhurried, careful assembly. Installation of the 4-VALVE® heads must be done by a person who has a working knowledge of the Harley-Davidson Evolution Big-Twin engine. This installation also requires a basic set of mechanic’s hand tools and some precision measuring tools. For obvious reasons, the installation instructions must be followed diligently and carefully. PLEASE DO NOT DO ANYTHING UNTIL YOU HAVE READ AND UNDERSTOOD ALL OF THE FOLLOWING INSTRUCTIONS!

The increased power obtained from the 4-Valve® will subject the drivetrain components to increased loads and stress. The condition of the flywheel assembly, clutch, transmission, chains and/or belts should be checked prior to installation of the kit. If assistance is necessary, contact your local Harley-Davidson dealer. These components may alter vehicle emissions and noise. Local and Federal laws should be observed. These components are for off-road use only.


Remove stock top end components in usual manner. Take care when transferring gasoline from gas tank to container. Only the rocker boxes and cylinder heads need to be removed. Retain cylinders to crankcases using one short stock head bolt and several spacers. If care is taken not to break seal of cylinder base gaskets, they will not need to be changed at this time. When installing 4-Valve® heads on 1984-85 Evolution Big-Twin engines you must use LATE STYLE 1986-up cylinder base studs, HD part number 16837-85 using care to set all at proper height.

Set up dial-indicator on front piston and find TDC. Set the indicator to read Zero at TDC. Now rotate engine backwards until the piston is down .248-in. Remove timing plug and stamp a new timing mark on the flywheel at this point. Use two dots or a (F). Do not use excessive pounding. This new mark is 25°.

Set up the dial indicator on rear piston and find TDC. Now rotate the engine backwards until the piston is down .248-in. Stamp a new timing mark on the flywheel at this point. Use three dots or a (F). This new mark is also 25°.

Remove dial indicator and re-install timing plug.

Using new head gaskets and ring dowel 0-rings, the 4-Valve® cylinder heads can now be installed. Rotate engine so that the rear cylinder is at TDC. on the compression stroke. If stock gaskets are used, they should first be sprayed with High-Temp aluminum paint. James head gaskets are highly recommended. Place new 0-rings on dowels first, then head gasket. Now place the rear 4-Valve® head on the rear cylinders ring dowels. If the fit of the new heads is tight on the ring dowels, care must be taken so that no damage is done to the gasket surface. An anti-seize compound should be used on head bolt threads and washers. Using a 3/8” ratchet and allen socket, get the two head bolts that come in the head started first. Next, install the other two head bolts and washers ensuring that washers are positioned correctly (flat down). Tighten bolts evenly using torque pattern shown later in this document. Take care that head goes on to ring dowels evenly.

Before torquing the heads, the intake manifold runners must be installed in the intake port counterbores. Each manifold runner has two 0-ring grooves and must have the 0-rings fully seated in each groove before it is pushed into the head. An 0-ring lubricant must be used so that no damage is done to the 0rings as the manifold runner is pushed into its counter bore. Once both manifold runners are in their proper locations, the intake plenum can be installed. Install the 0-rings in the manifold runner faces to be sure that they are retained in their grooves. The 0-ring groove is larger than the 0-ring to accommodate the material displaced under compression. Lubricate these 0-rings before you attempt to install the plenum. Now the intake plenum can be slid in between the runners. Take care not to shear off the 0-ring when the plenum is going in. The plenum is retained with two retaining rings.

Using a large pair of retaining-ring pliers, install one of the retaining rings in the grooves on the ends of the manifolds. Install the other retaining ring in the same manner on the other side of the plenum. If the heads are already torqued in place before the intake is installed, there is a good chance the 0-rings can be sheared off due to tight tolerances, causing vacuum leaks. For this reason, we recommend installing the intake first, then torquing down the heads, which gives the intake plenum a leakproof, tight fit.

Taking care that the heads are on the dowel pins, tighten both heads in the torque pattern. Pulling down evenly until they make contact with cylinders. Using a torque wrench, tighten both heads in sequence to 15 ft. lbs. Repeat procedure at 25, 30 and 40 ft. lbs. torque. Recheck all bolts at 40 ft. lbs.

Rocker Boxes

Rocker boxes are pre-set at the factory, but it is recommended that you double check swivel foot height (See diagram, page @ @ @). You will notice that the swivel foot closest to the pushrod end of the rocker arm is set and jam nut is tight. Remove the other adjuster and install adjusting tool (consisting of spacer-gauge bar and gauge mounting bolt.) Using a wrench, tighten bolt securely with the bar positioned over other swivel foot. Bar should just touch with no deflection or space between the two. If adjuster is not correct, loosen jam nut and adjust accordingly. Re-tighten jam nut. Remove tool, reinstall other swivel foot and run it in as far as it will go.

Install jam nut, but do not tighten at this time. Repeat procedure on all rocker shafts. Temporarily place out of the way.

Lubricate rocker box and spark plug 0-rings and install them into grooves on top of cylinder head. Take your time and make sure they seat fully.

IMPORTANT: Pushrod length is critical to operation of the 4-Valve® heads and will vary from engine to engine. It is highly recommended that you follow one of the below procedures exactly and make a set of pushrods for your engine. Adjustable pushrods are admittedly easier to use, but they can not compare to a solid pushrod for strength and durability.

It is recommended that you use an adjustable pushrod kit which includes two adjustable push rods and four unfinished rods and ends.

If your engine is basically stock and you want to retain your hydraulic lifters, we suggest you start with a good set of hydraulics such as Jims #2456.

If you are going to be using hydraulic lifters and they are already installed in the engine, proceed to installing rocker boxes.

If you have modifications done to your engine or plan to run it above 5000 rpm, a set of semi-solid rev ring lifters are highly recommended.

Remove lifter blocks from engine. Disassemble lifters as previously described. Add a little Type “A” automatic transmission fluid to bottom of rev, ring. Put back parts #2, 3, 4 and 5. NOTE: There must be fluid in the cavity below the piston. The reason for using Type “A” automatic transmission fluid is to get a quick drain down, and purge any air from under the piston. The purpose of keeping the rev ring and adjustment set tight is to prevent the lifter blocks from collapsing more than 1/32”, or the amount the cylinders have grown. Thus, valve timing will remain accurate.

Install the lifter blocks back in the engine, lubricating cam and lifters as you do so.

Installing Rocker Box

Start by turning adjustable pushrods to their lowest point. Lubricate ends with oil and install in lifters without pushrod covers. Carefully place rocker box onto head, taking care not to damage 0-rings and making sure pushrods are in rocker arms. Check to make sure swivel feet are flat on valve stems. Using liquid Teflon on the threads, install three center 5/16-18 x 1 1/2 allen cap screws and special washers into their respective holes (note that, in some cases, these bolts need to be in position before rear rocker box is installed). Next, install two 5/16-18 x 1 3/4 bolts and washers on cam side and three 5/16-18-3/4 washers on primary side. (Note that on final assembly, stainless bolt goes in center. Check length to ensure that the bolt is not confused with exhaust bolts.)

Re-check to make sure swivel feet are flat on valve stems and tighten bolts in sequence shown elsewhere in this manual. Draw down evenly to 15-18 ft. lbs. or 240 inch lbs. Record the torque you are using as you will want to use it on final assembly.

Procedure 1 — for semi-solid lifters

Turn engine over until one of the cam lobes for the cylinder you are working on is at its lowest point. Turn pushrod adjuster out until it takes two fingers and light force to turn the pushrod. Lock adjustment with lock nut. Repeat procedure for all pushrods. This is basically the procedure to adjust solid lifter and is the method we recommend. Loosen rocker box. If bolts are removed completely, make sure that the washers are also removed. Measure pushrods with a micrometer and record measurement and which valve it activates.

Procedure 2 — for hydraulic lifters

Turn pushrod adjuster out until it touches lifter and rocker arm securely with no “up and down” play. Mark flat part adjusters. Holding the bottom section, turn out the pushrod exactly three full turns (18 flat sides). Tighten lock nut to hold adjustment. Wait until you can spin pushrod freely before turning engine. Repeat for other valve. Loosen rocker box. If bolts are removed completely, make sure that the washers are also removed.

Measure pushrod with a micrometer and record measurement with which valve it activates. Repeat for other cylinder. Note that the previous information is for Stage I kits only.

NOTE: What makes this procedure work is that by pre-setting the valve adjuster in the rocker arm and locking it in place, the rocker now functions as if it had no adjustment. The adjustable pushrod is used only for measuring purposes to give us the proper length for the custom solid pushrod.

Cutting Pushrods

Using the measurements you have recorded for pushrods, deduct .500 from each total determined length to obtain desired lengths. Cut the pushrod with one end already installed to the desired length.

1) Using a metal lathe, shorten the pushrod the proper amount. Be sure that the reamed section is

still deep enough to accommodate the pushrod ball end. If it is not, ream it deeper using a 19/64”


2) Before installing the ball end, de-burr the pushrod. Also double check that you have cut it to the

correct length.

3) The ball end can be installed by holding the pushrod lightly between soft jaws in a vise. You can

provide a good solid base for the pushrod to stand on by using the pushrod socket piece from an

old hydraulic lifter. Place this on the vise center bar--the part that moves with the outer jaw. Hold

the pushrod up and down the installed ball sitting on the lifter socket. You can now install the

other ball end by gently tapping it with a hammer.

It may be helpful to use another lifter socket held with vice grips to drive the ball end in. This will protect the end from damage. Once the ball end is bottomed, don’t continue to pound on it. Damage to the pushrod and/or ball end may occur. Finally, check to be sure that both oil holes are open and that there is no debris in the pushrod. You should now be at your desired length.

Install o-ring in lifter block and rocker cover. Install new pushrods in covers--lubricate ends and install in engine following the same procedure you used for the adjustables. Torque rocker boxes.

If you are using hydraulic lifters, turn engine until any lifter is at its lowest point. Turn pushrod with your fingers making sure it spins freely. Carefully adjust swivel foot furthest from pushrod until it just touches the top of the valve stem and lock it in that position. Follow the same procedure for the rest of the pushrods.

When finished modifying the hydraulic lifter, you will be very close to a solid lifter running on a cushion of oil at start up. An as the engine warms up and grows taller, the oil fills the lifter to keep the adjustment consistent, producing the benefit of a solid lifter without the inherent problem of noise when hot.


The front rocker cover can be installed using the gasket supplied and the bolts tightened 6-8 ft. lbs. To install the rear rocker cover, the engine will have to be turned over until the intake valves are fully opened. Then the proper position of the rear intake valves can be obtained by blocking up the bike so that the rear wheel is off the ground, shifting the transmission to high gear, and turning the rear wheel by hand. The pushrod cover clips can now be installed.

The carburetor can now be installed along with the appropriate brackets. The cutout towards the front of the motorcycle is for the choke cable used with a 38mm Keihin carb. The cutout to the rear is for the 40mm CV carb. Install the top motor mount and torque the bolts 35-40 ft. lbs. Install the choke cable and make sure that the lock nut is tight. The ignition coil can now be installed in its place on the top motor mount (Stage II installations require a coil relocation bracket to clear the left carburetor).

The centrally-located spark plugs require that the spark plug wires have extra long boots on them. The silicone boots must be lubricated with a silicone dielectric grease so that they will go down fully over the spark plug. This will also prevent the boot from sticking to the spark plug insulator, making removal much easier. Stock Harley-Davidson spark plugs are fine for most types of street riding. If the engine is going to be run aggressively on the street, use Harley plug 5R6A or Autolite 4265.

Install spark plugs using an anti-seize compound on the threads. A length of rubber hose is helpful in getting the spark plug threads started. Care must be taken not to cross thread the spark plugs. You can visually observe this through the spark plug air cooling port using a flashlight. A piece of heavy wire is helpful in getting the plug straightened up. Once you are sure that the spark plug is started straight, the final tightening can be done with a universal type spark plug socket and a 3/8-drive ratchet. The universal action is needed so that the ratchet will clear the rocker cover. Using needlenose pliers, the spark plug boots can be pushed on down onto the plugs. Be sure you feel a click indicating proper engagement of the terminal end with the spark plug.

Install the gas tank. 1/4-inch spacers may be needed under the rear gas tank mount. This will give the additional clearance needed for the gasoline petcock to clear the rear cylinder head casting fins. A longer-than stock fuel line can now be installed. Next, install the special Anti-Reversion® exhaust head pipes. Apply a small amount of high-temp silicone to the exhaust pipe flange and gaskets. Also use anti-seize on bolt threads. Bolt pipes to heads. Mufflers can now be installed.


Installation of the 4-Valve® on the Softail is basically the same as for the FXR. There are a few extra things to be aware of. The rear exhaust pipe is a lot easier to install if it is bolted to the head before the head is installed. The rear exhaust pipe can still be removed and replaced on the assembled engine, but it is more difficult. The rear brake master cylinder reservoir must be relocated using the bracket provided. It needs to be moved to the left slightly so that front exhaust pipe will clear.

The clutch cable needs to be re-routed under the spin-on oil filter so that it will clear the exhaust pipe. The special muffler mount supplied must be used. The ignition coil must be relocated using the special bracket provided for this purpose. Long-boot spark plug wires must be used, but are a different length than those used on the FXR. Gas tanks fit with no extra hardware. A button head 1/4 x 20 allen screw must be used on rear cover so that the gas tank won’t hit it.



Proper engine tuning is very important and necessary to obtain the performance one expects from the 4Valve® heads. Performance gains can vary considerably from subtle changes in tuning. What types of carburetors, exhaust systems and ignition timing are used all have a profound effect on the amount of performance obtained. We have tested several combinations and feel that the information provided below satisfies these general tuning requirements. Special applications such as Big Bore and Strokers need to be dealt with on an individual basis. Direct all questions to


There are several different kinds of ignitions to choose from today. All of them will work satisfactorily with the 4-Valve® heads. They all have their advantages and disadvantages, depending upon the applications. Our recommendations are for stock application but will still be fine for racing. The Stage I application was developed to optimize the low-rpm torque most riders prefer. The stock Harley-Davidson ignition is well suited to this type of performance. Our recommended ignition timing is 25°. A Stage I engine can run safely from time to time at 5500 rpm. If this is desired, then the stock ignition will need to be replaced. The Dyna S Single-Fire Ignition was tested with excellent results. Also available is a Dyna RPM Limiter that is adjustable. The Single-Fire ignition had superior starting characteristics. These ignitions will work well for Stage II and above applications. If race gas is used, ignition timing can be advanced to 30°.


The 4-Valve® heads were designed to accommodate almost every carburetor on the market. Special adaptors and manifolds are available upon request. For Street performance the stock carburetors are fine. The Stage II version which has a dual-carb plenum intake, really allows the 4-Valve® heads to breathe, and with two stock carburetors has excellent driveability. Again, depending upon the application, the tuning requirements may change. All of our testing was done at sea level. If the motorcycle is going to be operated at higher elevations, leaner mixtures will be required. All of the carburetors tested were for street use. Dual 40mm Keihin constant-velocity carbs are the best choice for Stage II applications. They provide the greatest amount of legroom, and retain almost-stock appearance. They have been tested on engines up to 98 cu. in. with excellent results.


Peak power is achieved at 5500 rpm with any Stage I combination. If a vehicle is equipped with an ignition that will allow 5500 rpm, a set of S&S semi-solid “Rev-Ring” is highly recommended. Running a Stage I engine at 5000 rpm will work fine with unmodified hydraulic lifters. 4-Valve® heads are designed to accommodate cams up to .500 lift. Using cams that are not compatible with the 4-Valve® heads will result in poor performance and WILL CAUSE SEVERE ENGINE DAMAGE.

A Stage II combination begins with a dual carburetor conversion. The dual carburetors are necessary for anyone wishing to obtain the maximum potential of the 4-Valve® heads. Dual carburetors used in conjunction with the other Stage I components allow the engine to make peak power at 6000 rpm. Again, semisolid adapters are necessary for this engine speed. The 4-Valve® will work fine at this performance level without other modifications.


All testing and tuning was carried out using the Anti-Reversion® exhaust system. This system consists of independent header pipes that have the patented ANTI-REVERSION® balls in them, and special low-restriction mufflers. This system works best with the high flow blunt-taper mufflers. Traditional long taper mufflers are also available. These mufflers are quieter, but are slightly more restrictive.


4-Valve® heads and exhaust systems are designed for RACING purposes only. As the laws differ from state to state with regards to emissions and noise, local and Federal laws should be observed.


All 4-Valve® heads are warranted to be free from defects in material and workmanship under normal use and installed, as per installation instructions included, for 90 days from actual date of purchase to the original purchaser. Any modifications performed to the heads by purchaser will void this warranty. If any parts other than recommended camshafts and pushrods are used, the warranty is void.

Seller further warrants that products that were designed for a specific purpose shall perform for that purpose when installed exactly as defined in the installation instructions that accompany the products. Seller’s liability shall be limited to repair or replacement of any part found to be defective, free of charge at its plant. This warranty shall not apply to any product which has been repaired or modified by any person not authorized in writing by the manufacturer.

In no event shall the seller be liable for consequential or special damages to be from improper installation of purchased components.


Purchasers understand and recognize that RACING parts and accessories such as 4-Valve® heads sold by American Quantum are exposed to many and varied conditions due to the manner in which they are installed and used. Purchasers expressly affirm that they are relying upon their own skill or judgment to select and purchase suitable products and install them correctly according to instructions supplied.

Head Bolt Tightening Procedure:

Torque the bolts in the front head following this procedure, then repeat for the rear head.


Piston-Top Valve Reliefs


Crankcase Venting For ‘93 And Later EVO

The rocker box covers must be modified to provide for crankcase venting. 1) Drill and tap both rocker box covers for 1/8 x 27 NPT between the triangle webbing as shown in

the drawing. 2) Install 900 1/8 x 27 nipple style fittings for 1/4 minimum hose (you can use larger if you wish). 3) Vent both lines overboard and do not connect them together. 4) In the event of an engine with extreme blow-by, you can add some filter material in the triangular

area of the rocker box cover.