crankshaft/harmonic balancer bolt spins

[chevyguy82]

i was having an assistant turn the motor on cranshaft bolt to find top dead center with 3 plugs out and then the bolt keeps spinning. it won't tighten down. the threads look good on the bolt. is there any way to fix this? can i get a new bolt or is the crank ruined?

 

[blazinzuk]

If the bolt will not tighten down then more than likely your crank is ruined.

 

[Fordum]

Do you know the history of the engine?
I'm thinking wrong bolt. Either wrong size (metric vs sae) or too short.

Unless someone else has a better idea, I would pull the balancer and inspect the threads in the crank to see what stripped.

Depending on the amount of metal, if the crank is stripped, you May be able to drill it and go with one of the thread repair thingys or tap it larger.
Or maybe go with a longer bolt if there is enough threads deeper in.

 

[4X4HIGH]

The bolt "should" strip far before the threads in the crank would. Like someone already said, make sure it is the correct length and size of bolt (should be a 7/16" x 20 thread and not sure on length but about 2 1/2" seems about right).