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#1
06-15-2026, 10:57 PM
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Opinions On This “Line”
Im reassembling my motor and noticed this.(see pics)
Any ideas on this straight line on the snout of the crank? Ive never see this before. I sent this pic to my machinist. His response is that it’s not a crack Cracks dont create a straight line.
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 1966 GTO 1966 421-10.1-1 comp-Race Tec 23cc Pistons KRE Tri-Power KRE 65cc Aluminum Heads XE274 cam by Comp Cams DUR 230 Int 236 Exh @.050 - 110 LSA LIFT .491" Int .491" Exh Tri-Y-Headers by Tribal Tubes w/ Goerlich Mufflers 1966 Muncie Wide Ratio 4-Speed 1968-72 Chevy 12 Bolt Rear End w/ 3.73 rear gears |
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#2
06-15-2026, 11:05 PM
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Looks like a stress crack to me. Maybe your machinist doesn’t want to admit he missed it? I’m not sure you can drill a small hole at the end of the crack to create a termination point, kinda like glass. Not sure. Hope others will chime in.
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1964 Tempest Custom 421 SD clone KRE 74cc heads KRE 230°/236° hydraulic roller cam Rebuilt 3.23 rear end |
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#3
06-15-2026, 11:29 PM
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Can you feel it? Could it just be a stain from the keyway slot in the crankshaft timing chain gear?
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#4
06-16-2026, 12:20 AM
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I'd drill a tiny hole in the end of the crack as suggested above, and run it. Unless you are using it for direct drive on a procharger, it will likely look the same if you take it apart again in 10 years.
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#5
06-16-2026, 12:30 AM
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To me it's hard to tell from the photos. It could be a mark from when the key slot was machined or a crack. Personally I'd get some crack checking dye penatrant and it should reveal more.
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If it breaks. I didn't want it in the first place. _____________________________________________ 69 GTO \ 72 FIREBIRD \ 1/2 OF A 64 GTO \ 70 JAVELIN \ 52 FORD PU \ 51 GMC PU \ 29 FORD PU \ 85 ALFA ROMEO SPYDER \ A HANDFUL OF ODD DUCATI'S \ 88 S10 LT1 BLAZER & MY DAILY DRIVER 67 SUBURBAN. |
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#6
06-16-2026, 02:17 AM
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Is that on the drive side of the keyway or the back side? I should know by looking, but I don't
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I'm World's Best Hyperbolist !! |
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#7
06-16-2026, 02:43 AM
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Back side
Since the crank rotates clockwise, it's the back side of the keyway.
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#8
06-16-2026, 06:18 AM
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Timing gear had a burr to write that line. No worries.
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#9
06-16-2026, 09:31 AM
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Pull the key out, shine some light in there and take a pic at like a 45 degree angle toward that area.
Looking at it from the top with those pics it's hard to tell if it's a crack or just a groove/step. The key looks a little beat up on that side too, almost like the balancer was loose and hammered it. .
__________________
. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
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#10
06-20-2026, 10:49 AM
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I would check it with dye penetrant as suggested below. Or tape off the bearing area to protect it and see if a shop can mag particle test it while it’s assembled. If I was going to hammer on the motor I would want the peace of mind.
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#11
06-20-2026, 05:50 PM
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I like the dye suggestion, makes total sense....
.
__________________
. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
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#12
07-10-2026, 03:17 PM
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Sorry, for the late response. Took the crank back to my machinist and he looked at it. Not a crack but a groove from the harmonic balancer.
__________________
1966 GTO 1966 421-10.1-1 comp-Race Tec 23cc Pistons KRE Tri-Power KRE 65cc Aluminum Heads XE274 cam by Comp Cams DUR 230 Int 236 Exh @.050 - 110 LSA LIFT .491" Int .491" Exh Tri-Y-Headers by Tribal Tubes w/ Goerlich Mufflers 1966 Muncie Wide Ratio 4-Speed 1968-72 Chevy 12 Bolt Rear End w/ 3.73 rear gears |
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