Loosen the rocker or rocker shaft bolts. Leave the rockers on the head so that they will support the pushrods. Be sure the pushrods are standing free in the lifters and do not have any preload. Using the same reference point, place a 2nd mark on the pushrod. Make sure the angle and reference point are the same as the first mark.
You now have two marks on the pushrod; one with the assembly bolted into place as the motor will run, and the second mark with the lifter unloaded. The distance between these two points will represent the amount of lifter preload present.
If you find that the preload is not within +/- .010” (High Energy lifters) range of your specified preload, adjustability will be necessary. The simplest way to accomplish this is by using different length pushrods. COMP Cams carries a full line of pushrods for such instances. When measuring to find the correct length needed, be sure to include the amount of preload that the lifter requires in the measurement.
If your engine has pedestal style (bolt mounted) rockers, you can use shims under the pedestal to lessen the preload. This method also works for shaft mounted rocker systems. Longer pushrods will be needed for insufficient preload.
In most cases, you will only need to check one intake and one exhaust pushrod; however, if your valve stem heights are not equal, you will need to check preload on each valve. If this procedure is not followed, it will almost certainly result in a poor running engine and ultimately engine failure.
If you do need different length pushrods, call CAM HELP at 1-800-999-0853. We offer a large range of pushrod lengths and wall thicknesses, which can be sent out within 24 hours to minimize your engine down time.
Q. Are there benefits to switching from a flat tappet to a roller lifter setup?
A. In nearly all circumstances, a good roller camshaft pattern will outperform it’s flat tappet counterpart. Among the benefits of roller cams are reduced valve train friction (often good for a 20+ hp increase by itself) and higher engine rpm capability with little effect on low speed drivability and power.
Roller tappets are reusable, which makes it possible to swap just the camshaft without the expense of new lifters. Lastly, the faster, more modern lobe profiles available for roller cams produce superior horsepower and torque by snapping the valve open and closed more quickly. |
Q. Which lifter and cam type is best?
A. This will vary based on your application –we strongly advise pre-purchase research to determine which will be the best fit for your needs. The following are a few general guidelines about each camshaft /lifter type:
Hydraulic flat tappet lifters -Inexpensive, good compromise between low maintenance and good performance capabilities. Drawbacks include limited rpm potential (OE-style hydraulics) and the need to adhere closely to break-in procedure in order to avoid accelerated wear.
Hydraulic roller lifters- Similar advantages and liabilities to hydraulic flat tappet, but can produce higher power output and a smoother idle for the same RPM range due to advanced lobe designs and reduced friction. Requires no special break in procedure beyond correct installation and setup. Primary disadvantage is that hydraulic roller lifters are much more expensive than hydraulic flat tappet lifters –though most converts readily agree that the swap is well worth the extra money.
Solid flat tappet lifters- Inexpensive high performance, high RPM design. Drawbacks include the need to adhere closely to break-in procedure in order to avoid accelerated wear.
Solid flat tappet lifters also require periodic valve lash inspection and maintenance for durability and best performance, and can be somewhat limited in drag race applications by the amount of valve spring pressure that can safely be run.
Solid roller lifters- the ultimate high RPM/horsepower cam and lifter combination. Can utilize more aggressive lobe profiles than any other type of lifter. Minimal friction, and little to no valve spring limitation. Requires no special break in procedure beyond correct installation and setup. Primary disadvantage is that solid roller lifters are much more expensive than flat tappet lifters. Solid flat tappet lifters also require periodic valve lash inspection and maintenance for durability and best performance. Solid roller valvetrains are the standard in virtually every competition class that permits them.
For assistance selecting valve train components for your specific vehicle call our CAM HELP™ line at 1-800-999-0853 and speak with one of our expert technicians.
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