THE SHOP

October '19

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40 THE SHOP OCTOBER 2019 BUILDING THE Nighthawk II LS PRECISION ENGINE crank gear features an option of three timing positions +/- 8 degrees (I chose zero). The timing chain is Cloyes' extreme- duty single roller. The cam gear (four-lug compatible with a front-mount, LS2-style cam position sensor) features Cloyes' Hex- A-Just eccentric, which allows cam timing from 0 to 6 degrees advance or retard, in 2-degree increments. With the crank No. 1 rod pin at TDC, I placed the cam gear timing dot at 6 o'clock and adjusted the Hex-A-Just eccentric at zero. The supplied Torrington bearing was installed to the rear of the cam gear (held in place with a dab of CMD lube to aid in assembly), with the black side of the bearing facing the block. The cam gear was secured with three ARP LS cam bolts (8mm x 1.25 x 25mm), with Loc- tite 242 applied, torqued at 25 foot-pounds. The sprocket gear teeth are profiled for a very smooth transition during operation. Although not really needed with this high-performance precision timing setup, we added a Cloyes chain damper 9-5491. This rub-block damper serves to dampen any potential oscillation of the chain. The damper mounts to the block via Dart's 8mm x 1.25 holes. Again, the damper was an option, but it can't hurt. This was mounted with a pair of ARP 12-point stain- less 8mm x 1.25 x 25mm bolts, with Loctite 242, torqued to 18 foot-pounds. RING GAP Piston ring end gap was set at 0.020 inches for both top and second rings. While Icon's spec sheet lists 0.004 inches of gap per inch of bore diameter (based on that, our end gaps would be 0.0165 inches), this is a minimum gap spec. For high-performance use, Icon recom- mended a gap of 0.020 inches. During test-fitting, we measured the 0.020-inch gap with rings straight out of the box, so no file-fitting was required. RODS & PISTONS The Icon pistons feature full-float 0.927- inch pins, secured with a single spiral clip at each end. As a result of our previous test-measure- ment checks, I opted to mix the rod bearings, using MAHLE CB-663-HNK in the upper locations and CB-663-HNKX in the lower cap locations. This provides us with a healthy rod bearing clearance of 0.0025 inches. Bearings were coated with Royal Purple Max Tuff lube. Rod bolts were lubed with ARP assembly lube and cylinder walls were coated with 30W non-detergent oil. A few strokes with plateau brushes finished our cylinders. Just to verify, we ran runout checks on all main journals. Our measurements obtained zero runout. With rod bearings installed and rod caps torqued, rods were clamped to our Goodson mic stand and bearing clearance was verified at 0.0021 inches. The micrometer stand comes in handy for a variety of measuring applications. Oil clearance was measured for each individual rod and bearing set. Piston rings were also verified for end gap on a per-cylinder basis. Once pistons and rods were connected with spiral clips capturing the floating pins, all rod/piston sets, bearings and rings were organized on a dedicated per-cylinder basis.

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