Since this has been brought up in another thread I thought it might be a subject needed to be covered. I personnally don't have 100% of all info but it'll be open for others who might know better details.
Not all SBC's had the bolt. Not all cranks will be drilled for it. Keep in mind this will apply to original pre '69 engines (please note this is from my observations over the past 35 years of playing with them). Now anything with a late '68 casting date or was produced from '69 on (possible to '73 on 307's) will have the crank drilled & tapped regardless of size or useage. Before '69 odds are it'll be more of a performance engine feature but I can not be 100% to prove this is a truthful statement. Then depending on the shop doing any work on the crank for performance of reconditioning work it could of been drilled & tapped for the bolt. Then I will even add the '78 up SBC based V6 as they will use the same bolt as the SBC on all displacements. Anything from '69 up production not having the bolt is out right missing it. When replacing one always use a Grade 8 7/16"-20 x 2 1/2" bolt with matching Grade 8 washers. I wouldn't stack thin washers to match the thick washer used, always use one the same thickness.
Now some personnal experience with this. Back in the mid '90's I picked up what was listed as a '67 283 that turned out to be a '68 307 that was suppose to be the V8 to originally go in to my '81 Monte but went into my '72 instead. It was already apart so I never thought about the bolt. When I rebuilt it I found out it wasn't drilled & tapped for the bolt when I went to put on the balancer. So with the typical methods a 22 year old will use I got it on. Everything was peachy until a couple years later. Getting onto I279 in Pittsburgh I was hammering through the 4 speed with high rev shifts & had an eye opening experiance, lanched the balancer off the front of the engine with it wound out at about 4500 on the tach. The damage was a out of round pulley, the balancer had the outer ring moved to an unuseable position, dented my frame, ripped the keyway off the crank chipping out a corner of the keyway slot, took chunks of concrete out of the Jersey barriers on both sides of the highway & some poor guys brand new rear tire. Bandaged it up with a new to me balancer & pulley, a new keyway & on the road I went. Later that summer I had to replace the crank since it happen again after starting the car but no launch this time. The replacement reman crank wasn't drilled & tapped. A year latter the 307 was replaced with a rebuilt 283 that had the crank drilled & tapped. Now I'm not sure if it wa because I used the first used balancer off the shelf or because the snout was worn from balancer removal/instalation. But if I knew better the crank would of been drilled & tapped when it was apart before I rebuilt the 307.
Remember my ramblings on the dates may not be exact but a ball park. It is 100% that all SBC's used in our cars did have the bolt, all production 262, 267, 305 SBC engines did have the bolt.
Not all SBC's had the bolt. Not all cranks will be drilled for it. Keep in mind this will apply to original pre '69 engines (please note this is from my observations over the past 35 years of playing with them). Now anything with a late '68 casting date or was produced from '69 on (possible to '73 on 307's) will have the crank drilled & tapped regardless of size or useage. Before '69 odds are it'll be more of a performance engine feature but I can not be 100% to prove this is a truthful statement. Then depending on the shop doing any work on the crank for performance of reconditioning work it could of been drilled & tapped for the bolt. Then I will even add the '78 up SBC based V6 as they will use the same bolt as the SBC on all displacements. Anything from '69 up production not having the bolt is out right missing it. When replacing one always use a Grade 8 7/16"-20 x 2 1/2" bolt with matching Grade 8 washers. I wouldn't stack thin washers to match the thick washer used, always use one the same thickness.
Now some personnal experience with this. Back in the mid '90's I picked up what was listed as a '67 283 that turned out to be a '68 307 that was suppose to be the V8 to originally go in to my '81 Monte but went into my '72 instead. It was already apart so I never thought about the bolt. When I rebuilt it I found out it wasn't drilled & tapped for the bolt when I went to put on the balancer. So with the typical methods a 22 year old will use I got it on. Everything was peachy until a couple years later. Getting onto I279 in Pittsburgh I was hammering through the 4 speed with high rev shifts & had an eye opening experiance, lanched the balancer off the front of the engine with it wound out at about 4500 on the tach. The damage was a out of round pulley, the balancer had the outer ring moved to an unuseable position, dented my frame, ripped the keyway off the crank chipping out a corner of the keyway slot, took chunks of concrete out of the Jersey barriers on both sides of the highway & some poor guys brand new rear tire. Bandaged it up with a new to me balancer & pulley, a new keyway & on the road I went. Later that summer I had to replace the crank since it happen again after starting the car but no launch this time. The replacement reman crank wasn't drilled & tapped. A year latter the 307 was replaced with a rebuilt 283 that had the crank drilled & tapped. Now I'm not sure if it wa because I used the first used balancer off the shelf or because the snout was worn from balancer removal/instalation. But if I knew better the crank would of been drilled & tapped when it was apart before I rebuilt the 307.
Remember my ramblings on the dates may not be exact but a ball park. It is 100% that all SBC's used in our cars did have the bolt, all production 262, 267, 305 SBC engines did have the bolt.
Last edited:
