If you run a BF40A, 50A or 90 - and probably other types - you probably have a timing belt tensioner design which does not maintain the tension as the belt stretches from use and age i.e. a belt which looks in good condition may have become dangerously slack. The timing belt spring exists only to set the initial tension, subsequently the spring has no function, because the tensioner pulley is locked in position. At about 500 hours on my BF50A the timing belt suddenly slipped 10 teeth from its correct position with disasterous consequences. The post-slip incorrectly timed intake valves hit the pistons and bent, the engine would not start or run. The head had to be rebuilt at a $2,000 cost, but it could have been much worse because somehow my pistons escaped serious damage from hitting the valves.
I had made the mistake of assuming that my Honda outboard engine toothed rubber timing belt arrangement would be similar to that of car engines, which typically go between 1,500 and 2,000 hours between recommended belt changes, usually with no intermediate adjustment.
I found out too late that Honda recommend re-tensioning the timing belt every 200 hours, i.e at about half the hours which led to my own belt failure. I have seen several posts which imply that these belts will last 1,000 plus hours without attention. However, my experience and a tensioner design which does not take up the slack, suggest that this would be very unwise. My advice is to follow the Honda recommendation, and re-tension the timing belt every 200 hours.
I had made the mistake of assuming that my Honda outboard engine toothed rubber timing belt arrangement would be similar to that of car engines, which typically go between 1,500 and 2,000 hours between recommended belt changes, usually with no intermediate adjustment.
I found out too late that Honda recommend re-tensioning the timing belt every 200 hours, i.e at about half the hours which led to my own belt failure. I have seen several posts which imply that these belts will last 1,000 plus hours without attention. However, my experience and a tensioner design which does not take up the slack, suggest that this would be very unwise. My advice is to follow the Honda recommendation, and re-tension the timing belt every 200 hours.