While tuning up my '79 Vette and getting ready to check the timing, I realized that the harmonic balancer is Not turning. Can I remove it while on the car? Am I likely to find the crankshaft damaged or just the wordruff key sheared? Car still runs. Can I leave it alone for the winter? Thanks, Mike

 
Sooooo.....none of the belts are turning, either? That's a first! Possible the keyway have been sheared, but...Ida know...if the crank has been spinning inside the balancer, chances are one, or BOTH, are damaged. I'd recommend removing the balancer(it can be done in the car) and giving the crank a really close look....maybe take a micrometer to it to see if it is worn down. Also make sure the keyway groove isn't damaged.

Hi Joel, Pulley and belts are turning so crank is spinning inside the balancer. Best case key is sheared and balancer can be replaced; worse case:short block rebuild? Thanks,Mike

Well if the crank pulley is turning but the harmonic balancer behind the crank pulley isn't tuning with the pulley I would think the rubber insulator ring between the balancer hub and the outer balancer ring is kaput. Hence, you need a new balancer. 

Thanks Sarge,

Yeah...a little confusing on the description. If the belts are turning, the balancer is turning. The outer ring may be loose due to all of the rubber insulator being gone, as Sarge says, but....the outer ring should still be turning with the crank just from friction, unless it it hung up on something. Either way, that thing should be makin all kinds of noise, I would think. Still comes down tot eh balancer needing to be replaced.

The belt pulley turns but the balancer does not.

Yes you can replace it in the car. You'll have to remove the cooling fan and the fan shroud to give you a decent amount of room to access it. If you don't have a tool(s) for removing and reinstalling the balancer, you should be able to rent them from a auto parts store. Never use a hammer to put the balancer on. You'll mess up the thrust bearing inside the engine. Once you get the crank pulley off you'll see if the outer ring came loose from the hub. If you can, post pics for us to see what you have going on under there. 

Yes, we want to see pics of the carnage!

I'll dig into it this weekend!