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Discussion Starter · #1 ·
Had a 383 stroker in my 74 Nova. The guy that built it neglected to use loctite on the rod bolts. Short story nut came off, rod cap went under the crank and wedged in a cylinder. Block is screwed as is the crank. Jacked 2 rods that need replaced and 1 piston. When I rebuild it will not be raced on the track. Will just replacing the broken parts suffice or go all new. Any experiences will be helpfull.
 

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Loctite wouldn`t have made any difference. I`ve never used any type of thread locker on any of the bottom end bolts or studs. I`ve always used what the manufactuer recommended. If the pistons are pressed on you`ll need 2 new pistons as if a piston is pressed off there are usually cracks that develop and piston failure will occur.
Not being a smart a** but what`s your question?
 

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WWright said:
Had a 383 stroker in my 74 Nova. The guy that built it neglected to use loctite on the rod bolts. Short story nut came off, rod cap went under the crank and wedged in a cylinder. Block is screwed as is the crank. Jacked 2 rods that need replaced and 1 piston. When I rebuild it will not be raced on the track. Will just replacing the broken parts suffice or go all new. Any experiences will be helpfull.
The nut came off because either it was never torqued correctly or the rod or the bolt were moving around under the operating load. Rod bolts are not serviced with thread lockers.

The fastener is brought to a torque which is calculated to take the bolt into a portion of its plastic deformation area where the stretched out length is greater than the stretch it would see from operating loads being applied to it. An error either from not getting to the proper torque reading or arriving at the proper reading too soon against the stretch because of damaged, dirty, or improperly lubricated threads would leave the bolt insufficiently tensioned. If the operating loads exceed this tension, the bolt stretches and shrinks as loads apply and relieve when the engine passes thru its cycles. When the bolt stretches inside the threads the nut begins to unwind to relieve itself of the stresses it sees. Force takes the path of least resistance, this is not only true of electrical circuits, but is true, also, for mechanical systems. So a fastener is always looking for a way to relieve itself of the forces upon it. The solution is to use fasteners with greater strength that required for the applied forces and to pre-stress them at a level higher than the operating forces. Then no greater stretch can happen and the fastener will not unwind.

The rod can, also, move around under the bolt and nut if it is weaker than the bolt and nut and being subjected to more stress than its material or design can withstand. If its movement is greater and out of plane to the fastener, it can relieve the strain and let the fastener unwind. Or if the stress is out of plane it can bend or shear the fastener. Rod bolts see a lot of out of plane loads to where the whole assembly is hanging on the bolt's shear strength. On 383s with nut and bolt fastenings it is necessary to clearance the rod and bolt in the area of the bolt head to clear some of the cam lobes. These are the first I'd suspect as a likely failure point. Disturbing the surface of the upper rod shank by the bolt hole and the top of the bolt not only reduces strength by the loss of material, but removes surface compression of forged, headed, or rolled parts. This then allows these critical areas of the rod where the bolt head rides to be exposed to forces that are trying to escape at this point. The compressive surface on metals from forging of the rod to rolling and impact heading of the bolt helps keep the internal forces within the structural shape. If you touch these surfaces with a grinder, that area of surface compression is lost and forces looking for the easy way out will concentrate there. Clearancing rods and bolts for 383's must be followed by polishing and shot peening the re-worked surface. Otherwise, these areas will begin to skate around and will relieve the torque loaded stretch on the fastener.

I much prefer to use a cap bolt rod on these 383 and other stroker motors where parts need to be relieved for clearance. This configuration has the relief on a part of the rod where the load is now lower as it's being taken by the threads in the upper shank which spreads the load over more area than found adjacent to and just under the bolt head in bolt and nut configurations. However, even cap bolt rods must have the clearanced area polished and shot peened to restore the compressive surface layer of the forging.

Bogie
 

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ARP requires new bolt assemblies to be torqued, loosened and do it again 4 times because of this problem. Yours may differ not knowing what kind of bolt assembly you have. Just FYI
 

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Discussion Starter · #7 ·
Thanks for the input

The big question I had is it is more CHEAP to just replace the broken parts. Wondering if anybody had done the same and had luck. One block, crank, 2 rods, 1 piston = about 500 bucks. All new =about 1700-2500. I will stop being a tight a## and just get some new stuff.
 
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