What happens if your pushrods are too short?
If the pushrods are too short, the rocker arms may exert a side thrust against the valve stems as they push the valve open. This can increase friction, valve stem and guide wear, and increase the risk of valve stem breakage.
How is the length of a push rod determined?
To determine the right length, an adjustable pushrod is installed in the engine. The length of the pushrod is then adjusted so the roller on the end of the rocker arm is over the exact center of the valve stem when the rocker arm is at the halfway point of its maximum lift.
Can a push rod be used for a performance engine?
Original equipment pushrods have not changed much, but there is a growing demand in the aftermarket for stronger, stiffer pushrods for performance engines. Stock pushrods only have to deal with relatively light spring loads (less than 200 lbs.) and lower engine speeds (less than 6,000 rpm).
Why do pushrods have to be stronger than lifters?
On the other hand, increasing the rocker ratio also increases the effort required to open the valves because of the leverage effect. The higher the rocker arm ratio, the greater the force the camshaft, lifters and pushrods have to exert to push the valves open, and the stronger the pushrods have to be to keep from bending.
Which is worse a too short or too long pushrod?
A too-short pushrod positions the rocker tip too far to the intake (inboard) side of the valve tip. Conversely, a pushrod that is too long, positions the rocker tip too far outboard (exhaust side), forcing the roller tip potentially to travel off the edge of the valve tip!
What should the pushrod length of a valve be?
An ideal pushrod length will minimize the travel across the center of the valve tip. By shortening the distance travelled, we not only reduce friction in the engine but also reduce side loading on the valve tip, which is no small consideration when dealing with long, thin valve stems and high spring pressures.
Where do you put the pushrod on an engine?
Set up a rocker and pushrod assembly and rotated the engine through at least two full valve lift cycles. If the pushrod is too short, the mark will be toward the intake (inboard) side of the valve tip. If the pushrod is too long, the travel will be toward the outboard or exhaust side of the valve tip.
How does the rocker arm affect the pushrod length?
Since this raises or lowers the rocker arm relative to the cam, it needs to be factored into the pushrod length. Anything that changes valve stem protrusion also affects the needed pushrod length.