How to repair the Spline Cup (Driving Dog) on the rear hub of a BMW R75/5.
The Driving Dog is easily replaceable using specialty fasteners and common household tools.
This video (part 2) will show you how to use specialty aircraft fasteners (Hi-Lok) to bolt your new Spline Cup (Driving Dog) onto the rear hub of your R75/5.
The HI-LOK™ Fastening System is used in the aircraft industry as a replacement for rivets. They combine the features of rivets and bolts and are easy to install. It consists of two parts, a threaded pin and a threaded collar.
For more information on the HI-LOK™ system:
https://www.lisi-aerospace.com/products/fasteners/externally-threaded/pin/Pages/hi-lok.aspx
Tools needed:
1. 3/16″ allen head wrench
2. 5/16″ box end wrench
3. bench grinder, dremel, or sanding disk for drill
4. Sharpie
5. 10 each Hi-Lok Pins and Collars (Part#s below)
The Hi-Lok Pins I used (10/each):
HL20PB-8-10
The part# description: HL=Hi-Lok; 20=part number; PB=cadmium plated steel; 8=8/32″=1/4″ diameter shaft; 10=10/16″ unthreaded shaft
The Hi-Lok Collars I used (10/each):
HL1087ATW-8
Information about Hi-Loks:
https://www.jet-tek.com/hi-lok-pins/Hilok_Hitigue_Installation.pdf
Read the above PDF to familiarize yourself with all the different types of Hi-Lok pins, collars, and installation. You can use the exact same pins and collars I did successfully. However, if bargain shopping on ebay, you may also be able to use other pins (you will probably have to use the same collars I did). If I did this again, I would probably use the counter sunk pins, and counter sink the driving dog with a masonry bit to accept the counter sunk Hi-Lok pin heads. This way, it would not be necessary to grind down one side of the pin heads to sit flat against the driving dog.
You need to choose Hi-Lok pins with an unthreaded shaft size that does not leave any threads inside the aluminum hub or the driving dog. I measured the length necessary for my 1971 R75/5 aluminum hub and found that an unthreaded shaft size of 10/16″ would be perfect. Measure your hub bolt holes (with the driving dog sitting on it) from the surface of the driving dog to the surface of the aluminum hub bolt hole on the other side (I used a chopstick) first before ordering the Hi-Lok pins.
If you use the same pins I used, you will need to grind down one side of all the Hi-Lok pins so the pins will sit exactly flat against the driving dog. The driving dog has a curved surface on one side and will prevent the Hi-Lok pin from sitting flat on the surface of the driving dog if a side is not ground down. You want to prevent this and you also want to prevent the pin from spinning when tightening down the collar from the other side.
Installation is simple:
1. Place new driving dog on the hub
2. If using protruding head pins, grind down one side on each pin.
3. Mark the head of each pin both on the protruding head and the top of the bolt threads to indicate the side that is ground down. This will easily show you if the head has spun before you get the pin tight.
4. Using a 3/16″ allen wrench and 5/16″ box end wrench, tighten down the collar from the opposite side of the driving dog.
5. Tighten until the collar nut snaps off. The Hi-Lok collars nuts are designed to snap off at a predetermined torque. For this reason, make sure the pins are seated perfectly on the driving dog before coming close to the torque that will snap off the collar nut.
You are done!