Many downtime incidents on forestry equipment can be traced back to guards that came loose or fell off. Understanding the reason why guards often come loose can help you understand how to prevent this from happening. When a guard falls off it normally exposes a critical component that can cause or lead to a catastrophic failure of that important and expensive component. Most guards are mounted with soft bolts. Soft bolts allow the guards to receive wear and impacts without shearing the bolts off. Soft bolts normally stretch without breaking but this also means that they will require maintenance. Bolts in some guards that are taking impacts on a regular basis such as, harvester head or forwarder and skidder belly pans, may require tightening on a regular basis. From continual tightening or removing and re-installing bolts they can become worn. Soft bolts wear fast and therefore may need to be changed more often. However, soft bolts will not wear the threads of the frame components as quickly as hard bolts. Some think that using hard bolts should be better because they are stronger. Not necessarily, hard bolts will not stretch and can wear component threads and are very prone to shearing off. Washers are the key to keeping bolts tight. When both impact and vibration are present, two piece Nordlock or similar type washers are normally the most effective.
Best practice is to check guard bolts often, change bolts that are worn and replace washers that are missing.