A thought about timing belts on bikes getting onto 20 years n older...

[Greencan]

A thought….

...about timing belts, failure and its consequences.

A little while back my neighbour over-the-back-fence bought a 1990 ST1100, complete, albeit for a few pieces of small fairing components missing, for under $300. How come so cheap you ask, a broken timing belt.

Going back a little further, I responded to a thread within this forum to a topic, the originator of the thread advising that he had to replace 14 of the 16 valves as a result of a failed timing belt.

And this morning I again made comment on a thread lower down, the theme also concerned a timing belt.

So, as these bikes are getting on a tad in age and I could go on about other unfortunate souls who have similar tales of woe on failed or failing timing belts and its consequences, I thought I share a few pics with all you ST1100 home maintenance gurus to mull over…

Pic 1
This is a bog standard un-used OEM Honda ST1100 piston. NB its size and structure in relation to my thumb nail.



Pic 2
This is my Vernier set to inches and illustrating the width of the first 2 ring grooves, for the 2 compression rings. NB 1mm equals 39.370 thousandths of an inch. I hadn’t a new compression ring handy to show you, but take it from me when set in its groove it has approx. . .006 thou clearance, or about .15mm…not much eh!



Pic 3
This is the distance (in millimetres the top compression ring is set from the piston crown).



Pic 4
This is about the average rebate depth for both inlet and exhaust valves (in millimetres), on the swish area of the piston crown. NB the piston is of a bog standard forged aluminium…drop it from waist height and it will chip / bruise / and / or disfigure.



…as I said, just a thought

Cheers, the can :-)

[alans1100]

As they say "prevention is better than the cure" and why I did mine at 150,000km

[Greencan]

Mornin' Alan et al...

and why I did mine at 150,000km

...interesting kilometerage isn't it. I wonder if when Honda set that reccommended replacement distance that it was intended as a gaurantee?

:-)

[Kev Murphy]

Changed the timing belt on my 98st at 150,000. No visible wear but the old belt was around 4mm longer when compared to the new one, so a little bit of stretch had occurred. Very crisp performance after work done so timing must have been lagging by a minor amount.

[Greencan]

Mornin' Kevin et al....

but the old belt was around 4mm longer

...aah, I think you have hit the nail right on the head.

Interestingly in the OEM riders manual there are two (2), references to the maintenance of the timing belt, the later at 150k, which everyone knows and talks about and the other which seldom, or never gets a mention, at 100k. A clue to what Honda expectations of what is meant by inspect at this interval can be gleamed when the section on the timing belt in the OEM Service Manual is read. Worth a read sometime if your into doing your maintenance and the bike's odometer is nearing 100k.

I have 4 (or 5), cant acurately recall, used timing belts hanging up in the shed somewhere. One replacement I can quite clearly recall was so loose when saw it insitu, I was nearly ably to get it all the way off without releasing the tensioner. Another, off an ST I have owned since new had vertually no stretch whatsoever.

There was a reason for that

Just a thought.

The can :-)