My friend John's buddy brought his lawn mower to a lawn and garden repair center because it was making a clattering noise. The center told my friends buddy that there was a broken connecting rod and the mower wasn't worth fixing. When John took apart the engine he found that the original problem was that the connecting rod bolts were loose, which would have been an easy problem to fix.
1. Loose Connecting Rod

During the reassembly of the head, the center broke off one of the head bolts. In fairness to the center the bosses on the head are different heights and some of the holes are through and some were blind. To make up for the different heights, spacers were added to the shorter bosses on the blind tapped holes, to keep the head bolts from bottoming out on the imperfect threads on the bottom of the hole. I believe that the center didn't put a spacer under the head of the head bolt on a short boss with a blind hole and kept tightening the head bolt after it bottomed out and broke it. It is the upper right hand hole in the following picture.
2. Broken off head bolt

Here is a close up of the broken head bolt. you can see that the break is about 1/8" below the surface and you can also see that all of the holes are counterbored.
3. Broken off head bolt close-up

My go to method for broken off bolts is to TIG weld an extension to the broken bolt as shown below and then to weld a nut on the top of it. This method works very well for rusted bolts because the heat from welding expands the bolts and crushes the rust on the threads, to create some clearance.
4. Head bolt built up

5. Nut welded to head bolt
1. Loose Connecting Rod
During the reassembly of the head, the center broke off one of the head bolts. In fairness to the center the bosses on the head are different heights and some of the holes are through and some were blind. To make up for the different heights, spacers were added to the shorter bosses on the blind tapped holes, to keep the head bolts from bottoming out on the imperfect threads on the bottom of the hole. I believe that the center didn't put a spacer under the head of the head bolt on a short boss with a blind hole and kept tightening the head bolt after it bottomed out and broke it. It is the upper right hand hole in the following picture.
2. Broken off head bolt
Here is a close up of the broken head bolt. you can see that the break is about 1/8" below the surface and you can also see that all of the holes are counterbored.
3. Broken off head bolt close-up
My go to method for broken off bolts is to TIG weld an extension to the broken bolt as shown below and then to weld a nut on the top of it. This method works very well for rusted bolts because the heat from welding expands the bolts and crushes the rust on the threads, to create some clearance.
4. Head bolt built up
5. Nut welded to head bolt
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