Tech Tip 9 Correct Cam Bolt Tightening

Now, as a bolt is tightened it actually tends to stretch. A mild steel bolt tends to be softer and being more “elastic”, can actually stretch and contract quite a few times before metal fatigue sets in. These bolts however, are special “cam sprocket” bolts. That is, they are most likely harder than an off the shelf bolt. This means they can withstand the stress of their important job better than a “common” bolt can. The problem is being harder and a better grade of steel makes the bolts less malleable, that is they can tolerate over torquing even less than a softer mild steel bolt. When approaching their limit they will not stretch as much and just suddenly break!

These bolts broke inside the motor after some use, they simply were over-stressed from over-tightening and could only withstand the stress of running for so long. The interesting thing was the motor continued to run with the bolts in the condition shown. Note the polished shanks, they beat themselves against the interior bolt hole walls of the cam sprocket until they were the polished condition shown. Also note the cone shape of the ends, these were held down inside the cam just far enough to get a “purchase” on the cam and rotate it because there was a boss on the cam cover that held the bolts from backing out too far. So they beat and polished themselves by spinning and shucking in and out.