pvisseriii said:
I have read about many different methods of fine tuning. One way is notching the shaft key and another is offsetting it with a punch and vice.
Question is, with both methods offering relatively the same advantage, which method might be preferred and how many degrees does it give?
I've used the offset key for up to 3 degrees of timing change. I don't know how far you can go with it before the key gets too thin in the center, and shears. You can get a 5 degree change just by changing the sprocket and gear settings. I've also used the method acotrel mentioned, annealing the center of the cam sprocket and cutting more keyways. I made a jig to let me broach the new keyways accurately, but it didn't work out too well, so the new keyways were pretty randomly distributed. I cut 4 new keyways in one sprocket, for a total of 5, and two new ones in another, for a total of 3. Using them, I could usually find a combination to get the timing right, but it involved a lot of trial and error. I still think this is a good approach, but needs a better procedure to locate the new keyways more accurately. Between the sprockets I have, offset keys, and some use of vernier sprockets, I can accommodate my needs, so I don't have much motivation to pursue better tooling for the sprockets.
I've used vernier sprockets on the race engines with good results, but they do seem to need regular replacement. As hobot pointed out, the locating pins eventually wear the adjustment holes, and the timing slips a bit. Not a big issue on a race bike that is regularly torn down, but I wouldn't use them on a street bike that gets a lot of use. Again, I'm sure you could come up with an improved design for the vernier sprocket, but I'm not sure there's enough market out there to get anyone motivated to do so. Part of the problem is the small size of the sprocket vs. the number of holes needed to get a fine enough adjustment increment. For a brief while Fair Spares/Norvil sold a version with an aluminum sprocket. That was a real disaster. I tried one, and the pin beat the holes in the sprocket to death in short order. I've used the steel version Norvil sells more successfully, but it still wears eventually. The quality control is also not so hot, so the sprocket is typically not too concentric with the cam when installed, producing a big variation in chain slack as the cam rotates. Still, it seems to work well enough in the engines I've used it in.
Regarding offset keys, I make them up by starting with a thicker key of the right size, and file it by hand to get the desired offset. I've also done it by setting them up in the mill, but for one-offs it's not much quicker than making them by hand. It's pretty easy to calculate the amount of offset you need for a given timing change in degrees. You just need to keep the difference between crankshaft degrees and camshaft degrees in mind when doing the calcs.
The real solution would be for Jim/comnoz to incorporate a vernier mechanism in his gear drive conversion. Right, Jim? Just something to do in your massive amount of spare time.
Ken
Ken
