Column Theory
Because a pushrod is an eccentrically loaded column due to angularity load and arc motion within the engines atmosphere, whenever possible, it is most proper to use either a single taper or offset dual taper design pushrod. It is also very important to use the largest diameter pushrod that you can fit in the engine. This will help lessen deflection in the pushrod by putting the major diameter and mass where it is needed the most. The greater the angularity, the greater the arc motion. As the pushrod encounters this, the high load area on the tube moves closer to the energy source. The energy source being the lifter, as it travels up the ramp of the camshaft. It makes it even more important to use these tapered designs when using large roller bearing diameters, increased valve lash, very high engine speeds, high rocker ratios, rapid valve train acceleration and high spring pressure. These tapered designs make it easier for the pushrod to do its job properly, and will enhance the performance of all the other valve train components, which will enable the engine to produce the maximum possible horsepower. The tapered designs and large diameters will also reduce valvetrain harmonics. Do not be over concerned about pushrod weight. The difference between a stock 5/16 diameter pushrod in a small block Chevrolet and a 7/16 to 3/8 tapered pushrod, represents a difference of approximately 2.5% of effective weight. This is because the pushrod is on the slow moving side of the valve train. The effective increase in weight between the two pushrods may be small but provides a huge increase in valve train stability. Remember the valve side of this valve train is the critical side where any weight savings will make marked improvements. No matter what we change, valve train stability is the goal.

Important Special Instructions & Suggestions
It is very important to determine proper pushrod length. Improper pushrod length can cause a number of problems including excessive valve guide wear, lessened valve lift, valve stem side thrust, coil bind, improper valve to piston clearance and also rockerarm to retainer interference (in some cases lash caps can be used to help correct rockerarm to retainer clearance problems).

Check the radius of the lifter receiver cup and rockerarm cup/ball before ordering to help prevent mistakes. Improper ordering may result in parts failure. Watch for variations from stock radius in aftermarket lifters.

Make sure significant oil volume reaches the rockerarm end of the pushrod to help prevent galling due to excessive heat generation and lack of lubrication. To prevent interrupted oil flow to the pushrod, it is very common and almost always necessary to modify the lifter body so oil flows through it no matter where it’s positioned in the lifter bore (call for details). Oil restriction in the engine block is not normally recommended.

When possible, try to use larger diameter pushrods to spread out the load and lower the stress on the tube. This will help lessen pushrod deflection. Heavy wall tubing is a good idea also, to minimize compression. Many problems occur when a pushrod is inadequate for the application.

In high RPM applications tapered pushrods are a must for the serious racers. Tapered designs help to dampen harmonics in the valve train; extended valve spring life and increased usable RPM will usually be noticed.

Do not allow over clearancing for the pushrod. This may cause the pushrod to move around or deflect more than needed. Clearance of .010 at the closest point, wherever that may be during its complete cycle is sufficient. The cylinder head and engine block can often be utilized like a big guide plate and dampening device, which stabilizes the pushrod. Just make sure that there is no interference problems when turning the engine over on the engine stand.

Tapered pushrods should not be used in guide plate applications. Improper clearance and interference problems are sure to occur. Use only straight tube pushrods, specifically surface hardened for guide plate use in this application. Note: See series #2 and #4 for guide plate applications.

If you are using a tool steel rockerarm adjusting screw, it is almost always suggested that a tool steel pushrod tip be used at the rockerarm end. This will ensure proper compatibility.

Note: When using Manton pushrods, adjustments to valve/cam timing, valve to piston clearance and fuel curve may be required.