Well pinning the crank, 22mm version, has turned out OK so far. The biggest problem I've encountered to date has been getting a new key seat cut in the crank. When you live out in the middle of nowhere like I do your choice of machine shops is limited, and what I've run into is that nobody seems to have the right equipmet to do it. I finally found a guy that could do it and he did an excellent job. It ended up being kind of a 'buddy' deal, and he only charged me 10 bucks to do it, which I was needless to say happy about. I was prepared to pay alot more than that. We used a 5/32 woodruff key which we had to trim a little off the top of, but other than that it was pretty cut and dried. The 5/32 key is a little wider than the 4mm original so it engages a little more of the keyway in the sprocket, which should help a little strength wise. On the other hand the 5/32 key is not quite as thick as the 4mm so there was just a little bit of rotational play. The pins, as you'll see, took care of that quite nicely though. With the cost of the pins and the keyseat cutting, I'm into it about 25 dollars so far, so it has ended up being quite a bit cheaper than getting a new crank. Now on to the process.
I used the already drilled sprocket as a guide to drill on the crank. I didn't want to wallow out the holes in the sprocket any more than I needed to, so I just got the crank holes started and then pulled off the sprocket and finished them. The crank itself is pretty hard, so the Drill Doctor saw a lot of employment on this job. Once I got them to approximate depth (about 1/4") I put the sprocket back on and put the bit in the deepest hole and then tightened up the chuck on it, and drilled them to final depth using the sprocket as a stop.
There's how it turned out. The one piece of advice I can give on this is that if you miss on drilling your holes, miss towards the inside. If you get outside of that shoulder on the crank, that's where your seal rides....and that would be really bad.
Sprocket on with pins in. Obviously I'll trim the pins later. Just doing a test fit at this point. With just the woodruff key in there I did have a little tiny bit of play, but once I put the pins in.... That baby is tight!!! No play at all.
In looking back on this, the one thing I'd do different concerns drilling the holes in my jig. In doing that I had made an exact duplicate of the washer that fits inside the sprocket to use as a drill guide. Instead of making an exact duplicate, I'd make the larger diameter step quite a bit bigger. The smaller diameter step has to fit inside the sprocket but the bigger one you can make as big as you want. If you keep it original size you have hardly any room to operate when you're drilling the guide holes. I had a little trouble with the drill bit wanting to walk to the outer edge, so I think a split point bit would cure that. I drilled from the inside out, using the smaller step to kind of guide off of. I just eyeballed it but I think if I had to do it again I'd use a feeler guage of .005" or so between the bit and inner step to keep the holes a uniform distance from the inner sprocket wall. It still has worked out alright so far, but those are a few adjustments I'd make.
Topic: Save the crank I say!!!! Thoughts? (Read 6314 times)
