Performance & Hotrod Business - January '15

Issue link:

Contents of this Issue


Page 91 of 118

January 2015 n PRECISION ENGINE n 7 along with a set of Crane's rocker shaft 0.015-inch shims. Assembly of the shaft-mounted rocker system requires a bit of time, so patience is needed in order to properly position all rockers so that the rocker roller tips align with the center of each valve tip. A pack of Crane 0.015-inch shims is needed. Always place at least one shim between each rocker and each rocker spacer, (don't allow the rockers to run without at least one shim on each side). Additional shims may be needed in order to achieve rocker alignment with the valves. Crane offers these shims in packs of 32. (Total side clearance between a pair of rockers should be approximately 0.015 inches.) Note that the rocker roller tips do not need to perfectly center on the valve tips. Prior to installing the rocker shaft assembly, paint each valve tip with a black marker. Once the assembly has been installed and lash adjusted, you can roll the crank, which will cause the rocker rollers to leave witness marks on the valve tips. As long as the wit- ness marks are no closer than 0.040 inches from the edge of the valve tips, that's close enough. If rocker positioning needs to be cor- rected where side clearance is too tight, the steel spacers that are positioned between rockers can be flat-sanded to increase clear- ance where needed. (Note: Clearance between rocker arm and rocker shaft should be in the range of 0.0025 to 0.003 inches. Check this during test assembly. Use an inside mic to mea- sure rocker arm shaft bore and an outside micrometer to measure shaft diameter. Generally this clearance will be OK out of the box, but check it anyway.) Bench-assemble each shaft with rock- ers, rocker spacers and shims, locating the billet hold-down blocks in their appropri- ate positions, (five blocks per head). (Note: One side of each rocker shaft features a series of small oiling holes. When installed, these oil holes must face down toward the head, biased toward the valves. Some shafts may have oil holes that are in line with the bolt holes, and other shafts may feature oil holes that are slightly offset in relation to the bolt holes. The side of the shaft with oil holes must face down. If oil holes are offset, they must face down and be biased toward the valves.) Install the pushrods. Loosen all rocker adjusters in order to clear the pushrod tips initially. Place the rocker shaft assembly onto the radius-seat stanchions on the head and hand-snug the hold-down block bolts to the head. Thread the rocker adjusters to contact the pushrods. Inspect each valve location for rocker tip alignment; you want the rocker roller tip centered to the valve as close as possible. Note any locations that require alignment adjustment. Remove the shaft assembly, slide off the required rockers, spacers and shims (keep them in order) in order to install an additional shim where needed and reas- semble and reinstall to the head, and check spacing again. This may take a number of attempts, and it can be time-consuming, but be patient and pay attention by keep- ing everything in order. During test-fitting for rocker side clearance, I was forced to narrow a few of the steel spacers that are located between pairs of rockers, (flat-sanding on machin- ist's granite and emery cloth). Most of the spacers initially measured at 0.587 inches in width, and most required removal of from 0.004 to 0.007 inches. Each hold-down block bolt hole has a few thousandths of wiggle room, as do the bolt holes in the shaft itself, so it's tedious to factor in all of the tolerances when try- ing to obtain rocker side clearance. Once you've adjusted the lateral posi- tions of the rockers (for valve alignment), carefully disassemble each shaft assembly (keeping all pieces in order) and apply engine oil or engine assembly lube to the shaft bushing of each rocker and reas- semble and install. If the pushrod length is correct, you should have approximately 0.0370 inches of the rocker ball adjusters protruding from under each rocker arm. If vertical spacing is an issue (shaft too low in relation to pushrods), radius spacers are available to raise the shafts, (between the rocker stanchions in the cylinder head and shaft). One critical aspect of adjusting the shaft-mounted rocker assembly is obtaining a centered location of each rocker roller to each respective valve. Our Weiand Team G single-plane intake manifold provided an easy installation. While an out-of-the- box install would have been adequate, we took the time to obtain a perfect match-up between the manifold ports and the head intake ports in order to maximize flow efficiency, (as we do with all of our intake manifold-to-head fitments). During port match checking, only a minimal amount of port dressing was needed to obtain a smooth flow transition. The Weiand intake manifold provides a healthy rise above the lifter valley, providing an air space that minimizes heat soaking of the intake plenum and runners. Our valve covers are cast aluminum units from Summit, powder-coated in a wrinkle finish and CNC engraved.

Articles in this issue

view archives of THE SHOP - Performance & Hotrod Business - January '15