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Bulitpruf
by F.A.E.
More than Starters Our new BULITPRUF Chevy 139 tooth flexplate & Starter combination is now available! See our Pro Mod starter, so much HP you don't need 24 volts!
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How to properly shim a starter
Everybody has had trouble shimming a Chevy starter. Let's go back to basics. First lets describe what we are trying to do. Shimming is to adjust the backlash between the pinion and ring gear. To do this pull the pinion into the ring gear. One tooth of the pinion is to be between two teeth of the ring gear. We are looking for .025" between the tooth of the pinion and either one of the teeth of the ring gear. Let me repeat that .025" between the tooth of the pinion and either one of the teeth of the ring gear. We are NOT measuring between the pinion tooth and the valley between the two ring gear teeth. This is important. That measures a dimension called "clearance" (really!) in gear design, not backlash. The valley between the teeth is a non critical dimension in gear making and cannot be used to ACCURATELY measure backlash. Period. We recommend grinding the end of a .025 feeler gage about .125 wide by .5 long. When right it should slip in smoothly just like a valve adjustment. We don't recommend a round gage for the same reasons you don't use a round gage to adjust valves. A .015 shim changes backlash app. .003 but not always. As the gears get further away the .003 will become .005 or more. Once you have the proper backlash disable the ignition and spin the engine. Listen to it. If it sounds good you're done. If not remove one shim, spin the engine. Does it sound better or worse? If it sounds better remove one shim at a time till it sounds good. If it didn't sound better add one shim at a time till it sounds good. If the backlash was adjusted right one or two shims either way will be the most you have to go. If you start adjusting it 4 or 5 shims either way call me. The rest of this page is just nice to know info. Why do we have to shim the starter? There is a host of reasons. Minor adjustment is needed because of the stacking of tolerances and the pad mounting as used by GM. The reason racers have wide degrees of adjustment are caused by some other reasons. First the starter is mounted on the the pan rail. GM tolerances for the pan rail height are pretty tight. They don't want assembly line workers fighting with starters. Ever notice on stock GM starter a letter cast into the solenoid housing by the solenoid? This allowed the workers to use less or no shims by picking the size of the starter. Some of our aftermarket blocks may have pan rail height tolerances that are not as tight as GM. Second some aftermarket starter bolt locations are off. Some blocks such as DRCE blocks don't even come with them. There are at least two GM ring gears for the 168 application. One is .060" larger than the other. Both are used by aftermarket. Most are made offshore. Why do Bulitpruf starters sometimes use so many more shims compared to my old Hitachi style starter? The reason is Bulitpruf starter's pinion gears don't deflect under load. This requires a more accurate backlash adjustment. The Hitachi type starter pinion deflects so much under load that backlash has to be very tight during adjustment, but ends up very loose under load. This is why sometimes you can just throw a Hitachi style starter on and it works and no amount of shimming really makes a difference.
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