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techtalk:ref:engmech01h [2019/08/16 12:43] hippysmack [Test Fitting Cams] |
techtalk:ref:engmech01h [2019/08/16 13:26] hippysmack [Clearancing] |
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| ====== Clearancing ====== | ====== Clearancing ====== | ||
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| + | |The underside of the lifter bosses often need a little \\ grinding to keep the cam lobes from contacting. ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?p=668404#post668404))|Big cam lobes also may try to hit the pinion race, \\ which protrudes from the case slightly. It sticks out \\ farther on 2000-up motors. ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?p=668404#post668404))|If the lobe is contacting the pinion race, it's better to \\ modify the lobe than the race (this is a Red Shift 567). \\ Notice the chamfer on the lobe below. Modifying that \\ race is difficult and risky. People have done it and \\ trashed the bearing in the process. ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?p=668404#post668404))| | ||
| + | |{{:techtalk:ref:engmech:clearancing_the_engine_for_bigger_cams_1_by_aswracing.jpg?direct&300|}}|{{:techtalk:ref:engmech:clearancing_the_engine_for_bigger_cams_2_by_aswracing.jpg?direct&300|}}|{{:techtalk:ref:engmech:clearancing_the_engine_for_bigger_cams_3_by_aswracing.jpg?direct&300|}}| | ||
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| + | Another thing to check is tappet pin clearance. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?p=668404#post668404)) \\ | ||
| + | The tappet pin rests against the flat on the tappet to keep the tappet from rotating in the bore. \\ | ||
| + | But a bigger cam lobe lifts the tappet farther and on stock lifter, it can run out of travel. \\ | ||
| + | Aftermarket lifters as shown below sometimes have longer flats. \\ | ||
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| + | |Stock vs Jims lifter tappet flat comparison. ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?p=668404#post668404))| | ||
| + | |{{:techtalk:ref:engmech:tappet_pin_comparison_2_by_aswracing.jpg?direct&300|}}| | ||
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| + | Small base circle cams can help with all these clearances. \\ | ||
| + | It's because they achieve their extra lift, at least in part, by letting the lifter down farther as opposed to raising the lifter more. \\ | ||
| + | The 575's are small base circle so it makes them simpler to install. \\ | ||
| + | But small base circle cams often introduce one other problem and that's the clearance between the bottom of the tappet and the top of the cam bushing. \\ | ||
| + | When the lobe sets the tappet down, the roller needs to keep following the lobe. \\ | ||
| + | But sometimes with a small base circle cam the lifter will hit the cam bushing and thus not come all the way down. \\ | ||
| + | Easy to fix with some careful, slight grinding on the tappet on the underside of the axle support boss. \\ | ||
| ====== Test Fitting ====== | ====== Test Fitting ====== | ||
