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Don’t Neglect Your Timing Belt!

Tuesday, April 1, 2014

In today’s forklift truck marketplace many overhead cam engines (OHC) are used. The majority of designs use a timing belt setup that drives the camshaft and valve train assembly. Only a few manufacturers have used a timing chain setup with the OHC design in forklift applications. From our experience dealing with forklift truck dealerships nationwide, timing belt maintenance is often neglected. Resulting in bent valves or a shattered piston, failure to maintain your timing belt can be extremely costly. The following article will cover timing belt operation/reasons for maintenance and the proper procedures for changing a timing belt.

One of the many items inspected at each PM Service should be the engines timing belt. The technician should look for cracks in the belt, any type of excessive wear, fraying, missing teeth, etc. If any of these symptoms exist the belt must be replaced. The water pump runs off of the timing belt on certain models and therefore a worn water pump could cause a premature timing belt failure. Other items to check are the sprockets. The cam, crank and other sprockets do wear, the teeth become round and thin out. On Mitsubishi 4G63/64 engines, the belt tends to wear the oil pump sprocket more so than the others. Any problems with idlers or tensioners can also cause timing belt failure. Technicians must understand the belts importance and inspect the entire timing assembly upon each routine maintenance visit to avoid costly repairs that could have been prevented.

When changing the timing belt always put the engine at top dead center (TDC) compression stroke before removing the belt. If you remove the belt first and try to put the crank and cam pulleys on their marks afterwards, you will run the risk of a piston contacting open valves and have them bend. When the belt is removed visually checkout the associated components for wear as mentioned above. Any faulty tensioner or idler should also be changed at this time. The cam seal and front main seal should be checked for leaks. For balanced engines, always change balancer belts when changing the timing belt. Always matchup the new belts with the old belts. Count teeth, inspect for round or square teeth, and compare tooth pitch (distance between teeth). The belt styles may vary even for the same manufacturer due to changes in the production year breaks.

Always use the proper specifications and timing instructions before attempting this repair. All service manuals will show the timing mark alignment and will specify the proper tension procedures. For balanced engines, it is critical to follow the procedures to insure proper balancer timing. If the balancer is not timed properly severe vibration will occur.

Here is the listed order as explained:

  • Read timing belt section in service manual.
  • Set engine at TDC compression stroke
  • Remove timing belt.
  • Inspect related timing components
  • Inspect oil seals for leaks
  • Inspect water pump (if applicable)
  • Install timing belt
  • Double check timing setup
  • Tighten belt to proper tension as explained by the service manual.

For any timing spec’s, instructions or questions specific to your timing belt application please feel free to contact us at any time: 877/303-LIFT (5438)