I bought a D60 from another member who was honest about one of the threads being stripped on the pumpkin side for the spring plate. I looked into the different methods of repair and decided I want to run studs instead of a "U" bolt setup or bolts. I don't like the way the "U" bolt has to angle to miss the diff cover bolts, and studs & nuts are better then bolts. I can either run the stock stud 9/16 size after a thread repair or drill & tap for a 3/4 stud and just slot the spring plate for the bigger stud. My RuffStuff spring plate bolt slots are almost 3/4 wide anyways so it would only have to be widened a touch.
So to repair the threads properly you MUST drill them straight. You have to have a drill jig for this, so I machined one up. It will work like this. The Aluminum block has a .750 thru hole and a 1.002 counter bore. I am using hardened precision ground drill bushings to aid in the repair. First I slide in the 9/16 bushing that is .750 OD. in the .750 hole in the Al block, I kept the clearence to .0002/.0003 to it's a CLOSE fit. I screw in a 9/16 stud into the good thread. I line up the other hole as best as possible and tighten a nut with a good thick washer onto the 9/16 stud really tight. Then I will use a big "C" clamp over the near the hole being repaired so it does not "walk" or move around. IF this does not work to keep it from moving I have another method for securing it.
Then I slide in a 21/32 bushing and lock it in place with the set screw on the side of the Al block into the keyway cut I made in the bushing. This is an undersize drill for reaming. I drill the threads out. Then I replace the 21/32 bushing with an 11/16 bushing which is the correct hole size for a 3/4-16 fine thread. I ream the hole with an 11/16 reamer which will cut a perfect sized hole with a good finish on the bore. Then I replace the 11/16 bushing with a tap bushing (NOT SHOWN), This bushing will have a 3/4-16 thread inside and drive the tap into the casting and aid in threading it. Once tapped, I remove the tap bushing and clean out the tap cuttings and install a 3/4 bushing with a shoulder and thread in a 3/4-16 stud.
I tighten a nut onto the 3/4 bushing which locks down that side of the drill jig. Then I remove the nut & stud on the 9/16 side and repete the process. Then both sides will be tapped with a 3/4-16 thread exactly 3.250 apart from each other. I machined the holes exactly that far apart which is what there supposed to be. If I wanted to heli-coil it I could do that too to put it back to 9/16 size by using bushings for a Heli-Coil drill and tap.
So to repair the threads properly you MUST drill them straight. You have to have a drill jig for this, so I machined one up. It will work like this. The Aluminum block has a .750 thru hole and a 1.002 counter bore. I am using hardened precision ground drill bushings to aid in the repair. First I slide in the 9/16 bushing that is .750 OD. in the .750 hole in the Al block, I kept the clearence to .0002/.0003 to it's a CLOSE fit. I screw in a 9/16 stud into the good thread. I line up the other hole as best as possible and tighten a nut with a good thick washer onto the 9/16 stud really tight. Then I will use a big "C" clamp over the near the hole being repaired so it does not "walk" or move around. IF this does not work to keep it from moving I have another method for securing it.
Then I slide in a 21/32 bushing and lock it in place with the set screw on the side of the Al block into the keyway cut I made in the bushing. This is an undersize drill for reaming. I drill the threads out. Then I replace the 21/32 bushing with an 11/16 bushing which is the correct hole size for a 3/4-16 fine thread. I ream the hole with an 11/16 reamer which will cut a perfect sized hole with a good finish on the bore. Then I replace the 11/16 bushing with a tap bushing (NOT SHOWN), This bushing will have a 3/4-16 thread inside and drive the tap into the casting and aid in threading it. Once tapped, I remove the tap bushing and clean out the tap cuttings and install a 3/4 bushing with a shoulder and thread in a 3/4-16 stud.
I tighten a nut onto the 3/4 bushing which locks down that side of the drill jig. Then I remove the nut & stud on the 9/16 side and repete the process. Then both sides will be tapped with a 3/4-16 thread exactly 3.250 apart from each other. I machined the holes exactly that far apart which is what there supposed to be. If I wanted to heli-coil it I could do that too to put it back to 9/16 size by using bushings for a Heli-Coil drill and tap.
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