Warning: Timing Belt needs re-tensioning every 200 hrs on BF50A & others

[pcaker]

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.

 

[Skooter]

I had a similar incident on my 200, a pulley bearing flew off at +5000 rpm, cost me 24 bent valves, luckily no damage to pistons.

 

[dark_star]

It would be interesting to get Honda dude's opinion on this ?
I've not done this procedure to my 16 yr old BF50A yet. may be a time bomb though....

 

[hondadude]

The manual only states to inspect the belt. No mentioning of retensioning.

It probably is not a bad idea....it should not take too much time to do.

The only times I have run across a timing belt jumping time, at this point, is when there are mud dobber or critter nests in the timing belt area.....

Even in those cases the timing was only off up to three notches on the cam pulley. Just lucky, I guess.

Mike

 

[Deanmck]

As a BF50A owner, how on earth do I 're-tension' my belt. ie I have a pulley & a spring and not much else to play with.

 

[Skooter]

I know on the 200s the tension is not adjustable, it does have an automatic spring tensioner which self adjusts..perhaps the 50 is the same

 

[chawk_man]

Skooter - the timing belt tension IS adjustable on the 200 & 225. Look on pages 3-23 & 3-24 of your shop manual.

Deanmck - there must be a method for adjusting the tension. I just don't know what it is on that engine. Someone else will need to jump in on that. Maybe it would be wise to invest in the official Helm shop manual for that.

 

[jgmo]

Timing belts...being the flexible creations that they are....will inevitably stretch. On THAT I think we all can agree. But, the "elongation" each individual belt "experiences" will vary widely due to a number of factors for each individual outboard.

The variables will include, but are not limited to, some of the following:

How the outboard is used....IE: is it on a heavily loaded boat? does it experience frequent full throttle "hole shots"?
does it run at full rpm for long distances? does it do a LOT of sitting?

And, how and where the outboard is stored....is it stored in a slip? in a driveway? in the shade? in a "hot in the summer" barn? Is it in the tropics? is it in the far north....

I hope you see what I'm getting at. Variables such as these...and many more like oil or fuel leakage that gets on them can effect the way they will hold up over time.

The "warning" that pcaker gives comes from his (her?) practical and EXPENSIVE experience and, in my opinion, is one worth heeding. The only thing that I would add is that if I were to check a belt and find it had lost it's tension....I'm not 100% sure that I would just "re-tighten" it. I would consider what factors may have been at play to cause it to lose it's adjustment and correct any that I deemed might be altered to increase the belt's life.

But after doing that I believe I might still opt not to simply adjust it but strongly consider replacing it. Along with possibly a new pulley and spring if I thought that would increase the chance that my engine wouldn't self destruct. I have called that approach "cheap insurance" for a long time.

Like hondadude said....the service manual states "check the timing belt tension"....what you do after you find it loose is something else again.

 

[Shelldrake]

Hello,

My Honda 130 manual indicates check-readjust timing belt every 200 hours. Motor has approx 400 hrs. Should I take it to the mechanic for this specific service? I assume from the above discussion, that if it had stretched, it cannot be adjusted, but should be replaced?

Am I concerned about nothing here?

Thanks for any suggestions.

 

[Deanmck]

As far as I have found out & this more or less applies to my own bf50 motor. Readjustment of the belt tension is simply removing the plastic cover, releasing the tension on the pulley bolt thus allowing the spring to take up any slack and then retightning the pulley bolt. Sounds dead easy. I have recently changed my belt and sure as hell will not be waiting 200 hrs before checking it as I expect a bit of stretch in a new belt. I myself don't put too much trust in a wee Spring and will visually check that the belt is under good tension with a couple of taught millemeters play under tension. If of course anyone has anything to add/ check for I'm all ears.