April '17

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APRIL 2017 PRECISION ENGINE 3 PRECISION ENGINE EDITOR'S NOTE: The following is the second installment in a series documenting the build of an LS engine from a Motown II block. See part 1 in the January 2017 issue of THE SHOP magazine. W e've built a number of LS-platform engines over the past few years, in varying dis- placements and overall designs. In Part 1 of this build series we went over the block background, block machining and painting the block. In this segment, we continue with the cam bearings, camshaft, crank and rods, rings, timing and the oil pump. CAM BEARINGS The Motown II LS block features a cam bore with all five locations at the same diameter (measured at 2.282 inches). Cam oiling passages were also moved from the traditional LS position of 6 o'clock to 5 o'clock, to improve oiling with high-pres- sure valve springs. With the oil holes in the cam bores at 6 o'clock, the cam can be forced down under high spring pressure, severely restricting oil delivery to the cam bearings. The reloca- tion of these delivery holes to 5 o'clock eliminates that concern. While the GMP55 bearings feature a grooved outer diameter, it's still necessary to align one of the bearing's oil holes with the hole in the bore. The custom camshaft features journal diameters of 55mm (2.165 inches) in all five locations. World Products specifies the use of Durabond GMP55 cam bearings. The Durabond GMP55 bearings are available either coated or uncoated. I measured the GMP55 bearings with an outside diameter of 2.288 inches and an inside diameter of 2.174 inches. With cam journals at 55mm (2.165 inches), this provides a theoretical oil clearance of 0.0015 inches. Note: As delivered, the World Products Motown II LS block's cam bores featured slight burrs at the bore entrances, making cam bearing installation a bit difficult. We lightly chamfered each bore entrance prior Motown II LS Build Part 2 On to the crankshaft, cam and more. Build, text and photos by Mike Mavrigian Our short block is final- assembled. The Fluidampr crank damper will be installed after I finalize the appearance of our COMP timing cover. I may leave this bare or I may have it powder-coated in wrinkle black. Our SCAT forged steel crank features a 4.000" stroke and 2.100" rod journals. All journal dimensions were spot-on perfect. to installing the bearings. When planning a build using this block, just be sure to check the cam bore entrances and deburr as needed.

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