Cleveland harmonic balancer

[Scurt123]

I have a 73 mach1 with a 351 Cleveland motor. The motor has been together for about 8 years. It has a solid lift cam, roller rocker, tunnel ram and duel holly 450 carbs. It has run and performed well. All of a sudden it started throwi g the alternator belt. I've adjusted the alternator brackets and everything seems good there. Did that the crank pullyseems to have  about a quarter inc out from the crank. Everything seems tight. The balancer is two pieces with a rubber between. A friend said that this was probably the reason.  The pulley attaches to the center section and the bolt is tight to the crank. Is e balancer a 3 piece? Is the sleeve pressed in the center section? I haven't had the motor over 6500 rpm, and usually not above 6000. Any input. Just had the rear end rebuilt and some other thing over the winter. Would like to be able to start driving it. HELP.

 

[73pony]

Welcome from Iowa. It is possible you spun the balancer but if that was the case you should be getting some vibration while the motor is running. More so if it is extranlly balanced than if it is internally balanced but you should be getting vibration either way. Have you looked at the pulley alignment? Does it show a wobble while running. (Watch out while checking it you done get hit by the fan though.

 

[Scurt123]

I have checked and it is spinning true. Don't see any wobble.

 

[73pony]

Have you checked the alternator for excessive wobble or play? A bearing going bad in the alternator would cause enough wobble to throw the belt. As would the pulley not being true.

 

[Don C]

The pulleys bolt to the harmonic balancer hub. The hub slips (tight fit) onto the crankshaft and is held in place by the bolt in the end of the crankshaft. The balancer ring is held in place on the hub by the rubber insert. If the ring slips on the rubber insert it will not affect the location of the pulleys.

Are the crank pulleys too far out or too far in, in relation to the alternator pulley?

 

[Scurt123]

Out too far.

 

[Don C]

If the bolts that connect the pulleys to the hub are tight, the alternator hasn't gotten moved back, and the pulleys originally lined up, the only remaining possibility would be for the crank bolt to have loosened, allowing the harmonic balancer hub to move out. However, if this happened the timing chain crank sprocket would also be loose and I believe you would know about that by now. I would make sure the bolt that holds the harmonic balancer on the crankshaft is torqued to specs.