Valvetrain Facts

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A pushrod is an eccentrically loaded column due to angularity load and arc motion throughout pushrod travel. Pushrods want to deflect most toward the bottom of the column near the lifter side of the pushrod. This is because of the angularity load. In most cases it is best to use the largest diameter pushrod that will fit in the engine. The increased diameter will lessen deflection and allow better valve train control.

 

When checking and fitting for pushrod diameter it may be necessary to use a single taper or dual offset taper design, with the large end being toward the bottom. This places the larger diameter and increased mass properly to stiffen the pushrod where it wants to flex the most. The added clearance that the tapered design gives through the head and near the rockerarm can really be helpful. The taper on the tube can also help dampen harmonics in the valvetrain.

With a stiffer pushrod column, increased valvelift should be able to be measured statically in applications using a lot of spring pressure. The higher the engine speed the greater the increase will be at running speed. Keep in mind that by increasing wall thickness to a pushrod column does add strength, the percentage of increase is very small. The large gain in column strength comes from increasing the pushrod diameter.

Do not be overly concerned about pushrod weight. The pushrod is on the slow moving side of the valve train. The additional weight of a heavy wall pushrod usually provides a much needed increase in valve train stability.

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Note: In this simplified illustration, you can see that pushrod deflection and compression can cause reduced net valve lift, the result of a foreshortened pushrod. Valve timing (duration and timing) can also be affected by inadequate pushrod stiffness.
Note: Adding to the complexity of pushrod loading are compound angles resulting from offset pushrod cups (in lifters) and angularity relationships among the pushrod, valve lifter and rockerarm. Oblique angles contribute to side-loading and complex load patterns placed on the pushrod. Although some degree of pushrod “shock absorbing” is virtually unavoidable, minimizing such deflection and compression is critical for maintaining proper valve timing.
 
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Before we explain why we manufacture only modular pushrods, we must first stop and describe the function of a pushrod. In simple terms, pushrods transfers energy from the lifter to the rockerarm. If a pushrod is not correctly matched to the application, incorrect valve lift and valve timing can cause engine failure. With a properly matched pushrod you will achieve maximum horsepower and ultimate valve train wear.
To achieve the proper pushrod for an engine, you must decide the pushrod length, diameter, wall thickness, materials, heat treating and end configurations to match the specific engine components and application. This may seem like a fairly easy process but to accomplish this there are several things that must be considered. This is why we only manufacture custom modular pushrods.

 

  • 1. Each end in a pushrod must be compatible with its mating components. This requires the use of material that can function as a bearing and at the same time be as impact resistant as possible. As an additional benefit, this also allows for an unlimited amount of tip designs.
  • 2. With a modular pushrod it allows the flexibility to choose “unique” tapers for clearance issues. Also changing the wall thickness, diameter and tapering the tube will change the natural frequency.
  • 3. The column of the pushrod must be made out of a different material and heat treated differently than the tips. It must provide the strength to withstand the combined abuse of high engine speeds and cylinder pressure. By using a dissimilar material from the pushrod end we are able to utilize any heat treat we desire. In most applications we use a material that is commonly available 4130/4135 tubing. In our series 2 & 4 we use a MeloniteTM process for durability and wear resistance for guide plate use. In our series 5 we use a proprietary heat treating process to increase the material value to a Rockwell of approximately 46 “C”. This is critical to the function of a pushrod column and 4130/4135 is very tough, forgiving and durable when used at approximately 46 Rockwell “C”. We also offer a proprietary heat treated solid bar S-7 tool steel pushrod which is the same material used to produce quality chisels and hammers. It is very impact resistant and is the perfect material for extreme applications.

In our estimation the only reason to ever produce a one piece pushrod would be because of the reduced cost to manufacture. We are here to produce the highest quality pushrods available and for the reasons listed here we DO NOT manufacture one piece pushrods.

 
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Proper Pushrod Diameter

When checking for pushrod diameter you need to first establish the length needed. Then you must turn the engine over manually to check for tight clearance areas by the Cylinder Head, Lifer Bar and other close tolerance areas. We prefer .010 thousands at the Cylinder Head and .020 at the Lifter and Lifter Bar.

We prefer you to fit the largest pushrod you can in the area you have to work with. Sometimes small modifications need to be made.

Manton offers different size sleeves that fit over a pushrod tool to help assure proper clearance. The sleeve is used by sliding up and down the length checking tool with 0-rings holding the sleeve in proper position to assure clearance in these areas as needed.

 length checking tool with 0-rings holding the sleeve in proper position to assure clearance in these areas as needed.
 

Rockerarm Geometry and Proper Pushrod Length

 

Many variables directly affect determing proper pushrod length. Pushrod length is affected by all of the variables listed below.
• Block deck height
• Head deck height
• Cam base circle diameter
• Head stud boss height / rockerarm stand mounting pad
• Rockerarm design
• Lifter receiver cup height
• Valve stem height
 
Remember that every engine is different because the combination of these variables change from one engine to another. Take the time necessary to determine proper pushrod length with each engine you build. Do not assume that your pushrod length is the same as your friends engine. We have given some guidelines in this section to help you determine proper pushrod length for both roller rockerarms and shoe rockerarms. Each type of rockerarm style has different instructions.With shaft mounted rockerarms, raising or lowering the stands to change the rockerarm shaft height is usually necessary to obtain proper rockerarm geometry. With stud mounted rockerarms, changing the pushrod length achieves the same effect.

 

  • 1. Obtain an adjustable checking pushrod (available from Manton)
  • 2. Light duty checking springs must be used in place of valve springs to allow you to rotate the valve train and check for proper contact pattern on the valve stem.
  • 3. You will need an accurate measuring device to measure your adjustable pushrod once you have locked your adjustable pushrod at the correct length.
  • 4. Ball/Ball designs are to be ordered by overall length measurement. (The standard flat diameter on the ends of the pushrods is .100).
  • 5. Ball/Cup designs are most properly ordered by the effective length. This length is measured from the bottom of the cup radius to the tip of the ball. Overall length can also be given but tell us how deep the cup depth is. Make sure when ordering ball/cup pushrods that you specify effective or overall length.
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Proper Pushrod Length With a Shoe Rockerarm

See “Diagram A” for Shoe Rockerarm
When using your adjustable pushrod checking tool and checking springs you want the contact spot to start on the intake side of the valve tip with the lifter on the base of the camshaft (position #1). At approximately 1/3 lift the contact spot should be in the center of the valve tip (position #2). At full lift the contact spot should be the same distance past the center of the valve tip toward the exhaust side as it was when the lifter was on the base of the camshaft (position #3). Fully closed is back to position #1.

Proper Pushrod Length With Roller Rockerarms

See “Diagram B” for Roller Rockerarm
As in diagram A you should use a checking spring during this procedure. This allows you to rotate the valve train without damaging the checking pushrod and eliminates the unwanted deflection that would occur from spring pressure.

To obtain the roller positions listed below you will be re-locating the rocker arm pivot point (rocker shaft). By moving the shaft up or down the roller contact position on the valve will change.

With the valve completely closed and the lifter on the base circle of the camshaft, the roller should contact the valve at position #1 as shown in the diagram. As the valve train is rotated to 1/2 lift the roller will have traveled as far as it can and will stop at position #2. Continue to rotate the engine and at full lift the roller contact will be at its starting point. We will call this position #3. If the roller is not in exactly the same position at full lift as it was when the valve was completely closed, the rocker shaft must be moved. If the roller stops early the shaft must be shimmed up. If the roller stops late the shaft must be moved down. As you continue to rotate the valve train the roller will move back to position #4 when the valve is at half lift on the closing side and will finish at position #5 when the valve is completely closed.

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We offer many wall thicknesses which allows you to vary the frequency and column strength of the pushrod.
This provides a unique tunable valve train tool.