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When to do timing belt?

My Yamaha 115 4 stroke is 10 years old this summer. Low hours (around 400), but at what age do I need to consider replacing the T-belt and associated bits? Obviously when it looks deteriorated, but how many hours of operation or years of age is realistic? I'm and old guy and may be able to run this thing until I'm tired of it and sell it with the OEM still running, but I don't want to be pulling the head when I'm 80 years old...


  • sullmate
    sullmate Member Posts: 108 ✭✭
    it's time to replace. Yamaha recommends 500 hours for a timing belt change but time can cause weathering. 
  • formerlyFlyingV5
    formerlyFlyingV5 Member Posts: 23
    OK, here's the report. The boat is in the barn for Winter maintenance. I've removed the T-belt cover to have a look. The belt is in great shape.The label is not worn off, the tension is correct, and there is no sign of cracking or surface deterioration. All the idlers and WP are doing just fine. I have replaced countless T-belts on automobiles, and many were so bad the teeth were ready to fall off. The usual failure mode seems to be: cracks develop on the stretched side of the teeth, the cracks get deeper, and finally a tooth falls off causing catastrophic failure. This frequently occurs at shut-down, as the crank stops rotating and kicks back a few degrees in the opposite direction as it stops. There is always visible indication of imminent failure. This one looks OK. I see no reason to do anything to it now. When I see any wear or cracking of the belt, I'll do the whole kit. Or maybe it will last until I am done with it, and I'll let the second owner do it. I've torn down 16 valve engines with most of the valves bent and the guides split from bent valve stems, valve heads stuck in piston tops, etc., but I'm not worried for now.