250's have the fan belt grooves machined into the outer ring of the balancer. The load of driving accessories such as the water pump, alternator, power steering, air conditioner, etc. can cause the rubber bonding between the hub and the balance ring to slip. Pull the valve cover, watch the #6 cylinder valves as you turn the engine until they're "rocking" (exhaust closing and intake opening) and see where the timing mark and the distributor rotor is pointing. The dizzy should be pointing at the #1 plug wire (not #6) and the timing mark should be somewhere close to zero. If the timing marks don't align with the rotor pointing to the #1 plug wire, change the balancer.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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