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Hello everyone. I'm building a 5.3 truck engine (Gen 4) with a Blower Shop 6-71 for a '31 Model A sedan I'm building. I had the motor all done at a race shop and now I'm trying to get it all assembled. It's forged rods and pistons but it is the stock steel crank. TBS recommended an ATI Super Damper and I had the shop pin the crank like they recommended. My question is on the crank bolt. I bought a new ARP crank bolt and used my old one to install the dampener. There is a "hub adapter" in the TBS kit. The hole in it is only a 1/2" (.52") but the Crank bolt is .625" (I'm sure it's metric but I don't have metric mic's). I took a piece of tape and measured from the seating surface of that adapter down to the seating surface of the crank and it is 2.30" and the stock bolt is 4.20". So I would need a 6.50" bolt to make that work. I called TBS and he said they included a new crank bolt, which if they did I can't find it. But he said it would only be a 1/2" bolt. He said he couldn't say if I have some different thread size in the end of my crank, but the ARP bolt is right and it would be too large to go through the adapter. He said I could just drill out the adapter. I'm just looking for an opinion/experience if anyone has run into this with the crank bolt because he said the had not. There would seem to be a lot of torque on the bolt/damper/adapter plate/lower pulley so I want to make sure if I go to that long of a bolt it's ok IF i can get that bolt in that length from ARP. Any advice would be appreciated.
My first gen SBC is a similar setup. I wouldn't worry about the length of the fastener as long as it's the proper hardness. Machine the adapter to the correct diameter. And make sure you set the belt tension correctly. You will hurt stuff if it's too tight no matter what parts/setup you have.
Thank you. In talking with TBS again and looking at what I could find on line and talking to ARP, It appears the stock length crank bolt just goes in the damper and the 9 bolts holds the adapter and lower pulley to the damper. Thank you for the response.
I did what TBS said to do. Mine is a little different setup, but similar idea. Bolt your balancer to the crankshaft with the bolt, and then use the 6 bolts to attach your adapter/pulley.
I have an adapter hub mounted to the crank directly with the balancer bolt, then my blower drive pulley and alternator pulley are mounted using the same bolts to the hub My pulley fits over the adapter hub, to keep the belts closer to the engine.
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TBS 6-71 Lower pulley question 
