Torque / Tolerence Theory on Damper
07-22-2010, 08:23 PM
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Torque / Tolerence Theory on Damper We have four LS1 engines. Only one is giving us issues in the damper area and I want to understand why instead of just throwing parts at it until it works...anyone can do that.
The crank snout has a straight, non tapered OD. The damper has a straight non tapered ID. There is an interference fit of approximately 0.0012”. Based on engineering specs, that is appropriate for something that will only see reciprocating torque.
Unless the back side of the damper comes in contact with something, there is nothing but that interference fit to keep it from moving back toward the oil pump even further. The damper bolt keeps it from moving forward.
When you install your damper bolt, the shoulder of the bolt / washer combination presses up against the front side of the damper. As torque is applied to the bolt, the bolt drives the damper farther onto the crank. With each turn of the bolt, the damper slides back a little farther and the torque on the bolt increases until you reach the specified torque, then you simply stop. Breakaway torque on this bolt is not much, maybe 50% of final torque.
In theory and I guess reality, if that 0.0012” interference fit is compromised, the damper is automatically pushed back slightly towards the oil pump and the joint loses its clamp load and the bolt could walk out. If the bolt loosens, the joint loses its clamp load and the bolt could walk out.
So what could cause that damper to slide back even farther? If the engine was not properly balanced one could speculate that the vibrations are so violent that they are causing the damper to shift from fore to aft. What about the damper bolt? About the only thing I can think of that would be causing the bolt to come loose would be issues with the thread profiles on either the bolt or the crank snout. You could also have soft metal on the crank, but you would think with such high torque you would have already pulled those threads. Well, we have a new ARP bolt, our interference fit is good and everything is balanced and the threads show no signs of being pulled. The only thing I have not checked is thread profiles because I have a hard time believing that is the issue.
Anyone else have any ideas or theories?
The crank snout has a straight, non tapered OD. The damper has a straight non tapered ID. There is an interference fit of approximately 0.0012”. Based on engineering specs, that is appropriate for something that will only see reciprocating torque.
Unless the back side of the damper comes in contact with something, there is nothing but that interference fit to keep it from moving back toward the oil pump even further. The damper bolt keeps it from moving forward.
When you install your damper bolt, the shoulder of the bolt / washer combination presses up against the front side of the damper. As torque is applied to the bolt, the bolt drives the damper farther onto the crank. With each turn of the bolt, the damper slides back a little farther and the torque on the bolt increases until you reach the specified torque, then you simply stop. Breakaway torque on this bolt is not much, maybe 50% of final torque.
In theory and I guess reality, if that 0.0012” interference fit is compromised, the damper is automatically pushed back slightly towards the oil pump and the joint loses its clamp load and the bolt could walk out. If the bolt loosens, the joint loses its clamp load and the bolt could walk out.
So what could cause that damper to slide back even farther? If the engine was not properly balanced one could speculate that the vibrations are so violent that they are causing the damper to shift from fore to aft. What about the damper bolt? About the only thing I can think of that would be causing the bolt to come loose would be issues with the thread profiles on either the bolt or the crank snout. You could also have soft metal on the crank, but you would think with such high torque you would have already pulled those threads. Well, we have a new ARP bolt, our interference fit is good and everything is balanced and the threads show no signs of being pulled. The only thing I have not checked is thread profiles because I have a hard time believing that is the issue.
Anyone else have any ideas or theories?
