By far, the most common problem encountered when installing a new high performance camshaft is the incompatibility of the existing valve springs to the new cam. Factory valve springs are designed to work with stock, low lift camshafts, and since most aftermarket cams have higher lift, the springs must be replaced with compatible components. It is highly recommended and a requirement of the warranty that the suggested springs be installed along with any COMP Cams® cam. Most big block engines come stock with a double spring consisting of small diameter wire and many coils. Some people think that because it has double springs it is already high performance. However, nothing could be farther from the truth. This particular spring is one of the worst for accepting extra lift. Almost all big block engines will require a spring change along with the cam. Whenever installing a Hi-Tech™ racing cam in any small or big block engine, the cylinder heads must be equipped with the correct valve springs, screw-in studs, guide plates and hardened pushrods. The increased loads and ultra high speeds of the racing engines make this a necessity for valve train stability.
Small Block Spring Pockets
When machining a small block head for larger diameter valve springs, be aware that the area around the spring pockets in the head is very thin, especially the end or outboard exhaust. Care must be taken not to machine through the head when increasing the diameter of the spring pocket. You can round the edge of the cutter used to machine the pocket to resemble the diameter of the wire in the valve spring. Another way is to insert a .030” standard 1.250” diameter spring shim in the pocket prior to machining and cut only down to that point. The safest way is to seek professional help before ruining the heads.
When you are using a high performance camshaft and have problems with the valves not staying properly adjusted, one of the first things to check is the rocker arm studs. Most early model small block heads utilize pressed in studs. When high spring loads and high engine speeds are used with these stock type studs, they tend to pull out of the heads. You can check for this by laying a straight edge across the top of the studs to see if any of the studs are too high and out of alignment. If so, the heads should be removed and machined for screw in studs.
Factory small blocks were equipped with 3/8” studs and rocker arms. One of the most common practices on these engines is to replace these with larger 7/16” versions similar to those found on the big block engines. This is a simple conversion but requires a roller trunion rocker arm. See page 269.
In 1991 Chevrolet introduced the Mark V Big Block, which comes from the factory with a non-adjustable valve train. When changing to a non stock camshaft, the valve train must be converted to adjustable. We developed a special stud (Part #4514-16, page 277) to convert the heads with no required machining. Also on page 275 is a series of Magnum rocker arm kits engineered specifically for these engines that include this stud.
Flat Tappet Break-In
All flat tappet cams will require special attention during the break-in process. Due to recent changes in motor oil formulas, a switch to a diesel or non-synthetic racing motor oil in combination with COMP Cams® #159 Camshaft Break In Lube is mandatory in order to avoid camshaft failure during break in. Cams requiring dual valve springs during normal operation will also require that the inner valve spring be removed during break in so that critical lifter rotation can be established. The appropriate COMP Cams® lifters, and correct valve springs, rocker arms, and pushrods are also absolutely essential to ensure long camshaft life. Please refer to the instructions in your cam box for complete procedures or page for our tech bulletin on the topic If ever in doubt, please call the COMP Cams® CAM HELP® line at 1-800-999-0853.
Several points must be considered when installing a roller cam in an earlier block designed for a flat tappet cam. Flat tappet cams are ground with taper on the lobes to force the cam to the rear of the engine. Roller cam lobes are ground flat, so a thrust button must be used to keep the camshaft to the rear of the block. Most racing roller cams are steel billet cams, which require an upgraded distributor gear. Most street roller and hydraulic roller camshafts are made from an austempered material which is compatible with the standard gear; however, COMP Cams® composite distributor gear is the best choice.
Hydraulic Roller Cams
When installing a hydraulic roller cam in an early model block, it is necessary to use a special hydraulic roller lifter with a link bar assembly to keep the lifters from rotating in their bores. In addition, appropriate- length pushrods must also be used. A roller lifter, being physically longer, has a pushrod seat that sits closer to the rocker arm than a flat tappet lifter pushrod seat –necessitating a shorter pushrod. A thrust button is required to keep the cam from “walking” forward in the block. A wear plate is also a required (though inexpensive) part, which serves to prevent the rear of the camshaft gear of the timing set from excessively wearing the engine block as it works to keep roller cam walk under control.
When installing a flat tappet cam in a block originally equipped with a hydraulic roller, it is necessary to change the entire system. The cam, lifters, pushrods and timing chain set must all be changed in this case, as none of the old parts will interchange.
Self Aligning Rail Rocker Arms
Originally, the small block engine used a machined slot in the head to guide the rocker arm on the valve. It has been common to enlarge this hole and install a guide plate when switching to a high performance valve train.
In 1988 with many models and later, on all engines, Chevrolet utilized a small alignment slot in the valve tip end of the rocker where it contacts the valve. Although there may be an alignment guide on the head, it is not hardened and is used only to align the pushrod during assembly. This guide may not be used with a standard non-aligning rocker arm. When building a high performance engine, we recommend that the alignment guides, pushrods and rocker arms be replaced with the earlier style parts. When building a mild street engine, COMP Cams® developed the Magnum and Pro Magnum Rocker Arms™ designed specifically for the late model self-aligning design.
High Ratio Rocker Arms
A higher than standard ratio rocker arm moves the pushrod closer to the rocker arm stud. This makes it necessary to check the clearance between the pushrod and the head where the pushrod passes through. This is a very common problem and should be carefully checked whenever a rocker arm ratio change or pushrod diameter change is made. We offer a special tool (Part #4710) to machine this on page 339.
Rocker Arm Geometry
Proper rocker arm geometry is required to ensure the maximum benefit from any cam design. Camshaft base circle, block deck height, cylinder head design and lifter design all contribute to possible errors in valve train geometry. It is simple to make compensation with pushrod length. Usually, a longer than stock pushrod will be necessary in a high performance engine, but care must be taken to choose the correct length.
Rocker Arm Slots
One of the most frequent problems encountered when changing to a high lift camshaft is the slot in the rocker arm will contact the rocker arm stud, resulting in camshaft, lifter, rocker arm and/or stud failure. This is prevalent on both small block and big block engines with stock rocker arms. Always check this and change to either a roller trunion rocker or a long slot rocker arm when contact is evident. COMP Cams® Magnum Rocker Arms are a good solution to this problem.