PortaTree Timing Systems Tech Tip# 3

What you should know about Pushrods before you get into trouble !
By Terry Manton

Important Special Instructions and Suggestions

  1. 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, valve piston clearance and also rockerarm to retainer interference (in some cases lash caps can be used to help correct rockerarm to retainer clearance problems).

  2. Check the radius at 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.

  3. Make sure sufficient oil volume reaches rocker arm end of pushrod to help prevent galling due to excessive heat generation. (Although oil restricted pushrods are available, Manton Racing Products does not recommend them in most applications).

  4. When possible, try to use larger diameter pushrods to spread out the load and lower the stress on the tube. This will help lesson pushrod deflection. Many problems occur when a pushrod is inadequate for the application.

  5. 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. Increased lift at the valve will definitely be measurable.

  6. Do not allow over clearancing for the pushrod. This may cause the pushrod to move around or deflect more then 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, which stabilizes the pushrod. Just make sure that there is no interference problems when turning the engine over on the engine stand.

So... What is Column Theory?

Because a pushrod is an eccentrically loaded column due to angularity load and arc motion within an engine atmosphere, wherever possible it is the most proper to use either a single taper or offset dual taper designed. This will help lessen deflection in the pushrod by putting the larger diameter and mass where it is needed the most. The more angularity and arc motion the pushrod encounters, the highest load area on the tube moves closer to the energy source. The energy source being the lifter traveling up the ramp of the camshaft. It makes it even more important to use these tapered designs when steep ramps, large rollers on the lifter, increased valve lash, very high RPM, high rockerarm ratios, rapid valve train acceleration and stiff valve springs are used. These designs make it easier for the pushrod to do its job properly, and will enhance the performance of all the other valve train components to produce maximum possible horsepower. Do not be over concerned about pushrod weight. Be more concerned with valve train stability. The valve side of the pivot of the rocker arm is the critical side when it comes to weight.

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