July '20

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JULY 2020 THE SHOP 63 PRECISION ENGINE Morel also calls for lifter bore taper at no more than 0.0002 inch. Our bores were finished with zero taper. Once all block machining was done, I checked all threaded holes to verify that they were thread-tapped deep enough. No corrections to straight thread holes were required. We also checked the depth of all NPT (tapered thread) holes at the front and rear of the block, as well as oil holes in the lifter valley. Only one hole at the front required slightly further tapping—by a mere two threads—to allow the threaded plug to seat deep enough to avoid contacting the timing cover. Boring and honing left sharp edges at the bottom of the cylinder bores, so I care- fully deburred the bottom edges. This helps avoid potential scratching of the piston skirts and eliminates potential stress riser areas. Our attention then turned to checking crankshaft and connecting rod clearance to the block. With upper main bearings installed and lightly oiled, the crankshaft Instead of drilling deep into a counter- weight from the edge, drilling to accom- modate the tungsten slug was done by cross-drilling through the counterweights and reaming to size to provide an interfer- ence fit. Dart provided slight rod big end reliefs in the block as a starting point. I simply enlarged the reliefs in order to gain suf- ficient clearance for our stroker crank and rod combo. Our ICON forged pistons feature a relative- ly short skirt and lightweight construction while maintaining strength. The skirts are moly-coated to provide both oil retention and reduced friction. The dot on each skirt provides the skirt diameter measuring point. Due to varying diameters and barrel shapes of each piston, the manufacturer will indicate where skirt diameter must be measured.

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