Yes it is keyed to the crank. You still should check your balancer before you put it on and again after. The first thing to check is the rubber insert between the inner hub and outer ring. Make sure its still where it should be and not working its way out. Make sure the outer ring is still where it should be and not walking forwards or back towards the engine. Check the keyway for cracks or damage.
Once you think its OK to use go ahead and put it on. Never-never-never hit the outer ring trying to get the balancer on. Use a stud, nut,and washers with plenty of lube on the threads, and pull the balancer into place. If you must drive it on with force, only do so with caution, and only hit the inner hub area.
Also, once you have it installed, you should really check it for correct timing. The outer ring can move and often does causing incorrect timing.
You can rent a tool that screws into the #1 sparkplug hole that stops the piston from going to the top. You must use extreme caution and only use hand tools to turn over the engine once you install the stop!!!! What you want to do is turn the engine, by hand till the piston hits the stop. Mark the balancer with a marker at (0) on the pointer. Now reverse rotate till it hits again, a full 360 degrees the other way. Mark the balancer again at the (0) on the pointer. You now have two marks on the balancer and the actual timing mark should be right in the center of the two. If its not the outer ring has moved. Now you have two choices, one replace the balancer, or two, mark a new line. Eather way, your timing will be dead on.
I just bought a rebuild balancer for my 250 for $45 plus shipping. You might check around, they are cheaper then you think. Joe
