I have an aftermarket engine and crank. It has 2 keyways in the front. I'm trying to swap from a double roller back to a stock single roller. I removed the crankshaft gear just fine. But every time I go to install the new crankshaft timing gear the damn keyways slide just a bit and end up jamming the gear in place.
I've tried heating the gear and all that but this is not really the issue. The gear goes on fine. The problem is those damn keyways getting knocked out of place preventing the crankshaft gear from moving up any farther or even back out.
The keyways are so tiny and I think the oil I put on the crank to get the gear to slide on easier got into the keyway hole.
Arrg, thinking about trying superglue to try and hold it. But I can foresee the glue breaking free when the gear is being tapped on. Then I'll be in the same boat, keyway jamming the gear from sliding on.
Edit: I've used a wrench to hold the rear keyway closest to the engine in place but at some point there is no more room and I have to remove the wrench to get the sprocket on any farther. Only to be disappointed as the keyway moves back slightly and keeps the sprocket about 1/4" from being in place.
Tips on keeping keyway in place while installing crankshaft gear 
