SBC 305 Crank Snout Threads
12-22-2009, 01:05 AM
#1
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SBC 305 Crank Snout Threads I rebuilt a 305 out of an 84 C10 for a guy and I'm having some issues with weak balancer bolt threads. I installed the balancer with a proper installer. I chased the 7/16x20 threads with a tap before I put the bolt in. I was able to bottom the tap out by spinning it with my fingers, no force was used. Then I go to try and torque the bolt down to spec and it's just walking the threads in the snout.
7/16x20 seems like kind of a small bolt for what they're asking for torque wise. For those that might be wondering, I was barely able to get it past 15ftlb approx before the threads failed. By no means did I over torque it.
So my question to you would be... do you think I should heli-coil it back to 7/16x20 or open it up to 1/2x20 and use a big block bolt?
Something else I noticed was there seems to be a lot of extra thread in the snout that the bolt isn't using. I wonder if I could get a bolt about 3/4" longer to utilize the rear most threads.
7/16x20 seems like kind of a small bolt for what they're asking for torque wise. For those that might be wondering, I was barely able to get it past 15ftlb approx before the threads failed. By no means did I over torque it.
So my question to you would be... do you think I should heli-coil it back to 7/16x20 or open it up to 1/2x20 and use a big block bolt?
Something else I noticed was there seems to be a lot of extra thread in the snout that the bolt isn't using. I wonder if I could get a bolt about 3/4" longer to utilize the rear most threads.
12-22-2009, 12:21 PM
#4
let's say some one else needed to work on it and didn't know it had been changed to a bigger one. plus the BBC snout is bigger to hold a bigger bolt.
Other than that, I don't know, haha.
Never was a fan of over size bolts being where they don't belong.
Other than that, I don't know, haha.
Never was a fan of over size bolts being where they don't belong.
12-22-2009, 02:13 PM
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I talked to my machinist today and he recommended going 1/2". We weighed the different options and decided it'd be better to open it up to the next size rather than put a coil in it. From a mechanical standpoint I'd be more worried about a coil holding the amount of torque required by these bolts than the hole being a little bigger. It's still fine thread, it's just the next size up.
Thanks again for your input though.
Thanks again for your input though.
