Spun Crank Gear fixRemoving a stripped crank bolt, and repairing a spun crank gear
Quick premise: Crank bolt snapped getting up to speed on interstate. Pulley key wasted and crank Key slot partially boogered.
here is my fix pictorial:
- New Crank Pulley - VW (049-105-263-C)
- New Crank Bolt - VW (N-903-208-02)
- All New Belts
- Loctite (Stud and Bearing mount)
- 2 STD Roller Bearings (mid '70-'s Harley Sportster Trans Mainshaft)
- Brake Cleaner
- Good set of Cobalt Drill bits
- #5 Easyout (5/16) with 19/32 drill bit (if needed)
- 1/16, 5/64, 9/64, 5/32 Cobalt drills (if not in set)
- Flywheel lock (if you have one
- Torque wrench
- Center Punch
- 14mm x 1.5 Thread Tap (if needed)
1- To make it easy I removed: the timing belt cover, the Serp tensioner, right from wheel, lower timing belt cover and inner fender well.
2- Using a center Punch I made a mark in the exact center of the broken Crank Bolt. I started with an 1/8 pilot drill bit and worked my way up to 19/32 to extract.
3- I then took the new crank Pulley on the drill press with a 1/16 drill bit and drilled one hole opposite keyway and all the way through (you can use 2 dowel pins if your crank is really trashed). I drilled the pilot hole so it would be in the center of the crank between the crank bolt hole and the outer edge of the crank (SEE Hind Sight Notes at bottom).
4- using the 1/16 drill bit and the crank pulley placed on the crank as a template, I drilled the hole in the crank to a depth of 1/2 the length of the dowel pin.
5- I then used the 5/64 drill bit in the same fashion, drilled all the way through the crank pulley (using it as a template) and then into the crank to the same depth as #4.
6- using the 9/64 drill I drilled the crank hole out (not using the pulley this time) to same depth as above (1/2 the length of the dowel). Go back and forth a few times to make the hole a tad bigger. You could probably go to the 5/32 drill for the crank only so the pin slides right in, but I wanted a tighter fit.
7- using the 9/64 drill I drilled the crank pulley hole 1/16" more then 1/2 the depth of the dowel from the Backside out. This will prevent the dowel from backing out and allow and easy way to drive the dowel in to the proper depth in the crank pulley.
8- Drive dowel pin(s) into crank pulley
9- Tap crank threads (14mm x 1.5) to clean them up if necessary. I needed to because when the bolt snapped, it slightly screwed up the first 2 threads. The bolt must screw in perfectly by hand to be able to torque properly.
10- use brake cleaner to clean everything. I then used a small amount of Loctite stud and bearing mount on the crank key slot, than mate surface of the crank pulley and crank and then used regular red (271) on the bolt.
11- Torqued to proper specs (66 Ft'Lbs + 1/2 Turn) using homemade flywheel lock.
Hind Sight notes:
1 - If your crank key slot is really bad you may want to use 2 dowels on either side of the crank (away from the old crank key slot).
2- If I had to re-do, I would probably have drilled the dowel(s) closer to the outside edge of the crank (further away from the crank bolt). This is because there is less shear force the further out you go from the cranks center point. I was worried about being too close to the end of the crank, but in reality, that's where the stock keyway is...
This is just me over analyzing things as it will likely never matter anyway..
Good luck and be patient if you try to do this as well. A broken drill bit in the crank will give you a world of hurt. (light pressures to drill and straight holes)
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