FrontEngineDragsters.Org Forum
Technical => Matt Shaff's Engine Shop => Topic started by: MaggiFinn on July 09, 2014, 11:46:41 AM
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As we just finished fixing the deck on the 400sbc again, I wanted to share with you guys a link I found, regarding the effects of fine threads on stud pull when coarse thread torque values are used.
http://www.futek.com/boltcalc.aspx
When used in aftermarket engine blocks, the added clamping force from fine thread studs and nuts may be fine, but when using 40+years old iron the chance of pulling out threads and cracking components increase dramaticly.
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Interesting info but remember--on a 400 SBC it is 50/50 chance being cracked on the deck between bore and head bolt hole that is nearest the cylinder--hard to find one that is not --I see dozens throughout the year and many are cracked after clean up and inspection--it is a 400 Thang!
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Interesting info but remember--on a 400 SBC it is 50/50 chance being cracked on the deck between bore and head bolt hole that is nearest the cylinder--hard to find one that is not --I see dozens throughout the year and many are cracked after clean up and inspection--it is a 400 Thang!
I agree! The decks of my SBC 400 block (Chevy PN 776509) have probably half a dozen of cracks. There are cracks between threads and coolant passages, between threads and steam holes. On thread has two cracks 180 degreees apart, one to a coolant passage and the the other to a steam hole. This block is on borrowed time, but it's still going strong!
It's tall filled with HardBlok, the coolant galleries are about one inch deep.
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When preping a 400 CI block, I use Iron-tite crack repair plugs to plug the Steam Holes [after tapping hole with tapered tap]. Install with 609 Locktite-TIGHT. Cut off above deck and finish off when decking block. This seems to help control the potential for future cracks and limit those that have started. I will only use studs in these old blocks. Some blocks are so BAD that pulling out the threads cant be avoided. I check and repair all before doing any machine work. [Just remember to set repair insert below deck,so as not to hit it when decking] Its too bad many good 400 blocks went to the junkyard yrs ago. If needed I have a Std. bore 400 block that has been cleaned and pressure tested. Also has a set of 4 bolt steel caps/studs with it/but NOT installed. I am in North Central Ohio.