Broken Starter Bolt

[Keith_J]

Those bolts break very easy. Not too hard to get out. They’re standard GM starter bolts. You should check the bendix engagement and shim the starter if needed.

Starter bolts break because of fatigue. This is evident in the very low deformation of the fracture plane, the pieces fit together tightly. A bolt failure from transverse shear would show offset deformation. Tensile failure is indicated by necking or reduction of diameter at fracture plane. Torsional overload will have a corkscrew fracture indication.

Starter bolts fail by bending fatigue which is prevented by the bracket on the non drive end. The knurling of the shank imparts compressive prestress, exactly the same effect as shot blasting connecting rods. Fatigue affects higher strength steels to a greater extent.

The cause of this fatigue is the spur gear profile, required for pinion engagement. Every tooth makes one cycle. Without the rigidity from the bracket, the bolts are slightly bent each time a tooth on the pinion engages the ring gear.

 

[Indyharleyguy]

Hi I'm going through this right now. I'll find out in a few hours if I can easily get the broken bolt out.