On Dec 1, 2011, at 3:27 PM, Alasdair Cameron wrote:
> Anyone had much experience of the ExactFit timing belts?
>
> I fitted a pair of these belts to my ST4S a year ago and have covered around 12k km's on them.
>
> When I originally fitted and tensioned the belts, I used an IPod and some frequency analysis (tuning) software to set them to 110Hz at their respective TDC's. The belts are now at ~65Hz.
Although I have an Ipod and a mic the one thing that has always been troubling to me with the idea of a "freebie" method of sonic tuning is the problem of calibration of the instrument.
The chance that a mic made for $1 is spot on the money is pretty slim.
I was in the audio business for quite a while and I can tell you that even in *high quality* mass market products you are lucky to get a 10% tolerance.
So if you were aiming for 110 hz you could be anywhere from 100-120hz.
What tolerance they get on the built in mic is another question.
So when I fitted a set I used my tried and true 45 degree twist method and have had no issues.
I do think that the tighter fit of the belts would call in any allowances for slop that the originals allowed for.
In other words, just a little too tight would be bad whereas it would have been accommodated by the originals.
>
> Checking them now (post 12k km) using the "old school" method shows a fair bit more play than the 5mm deflection rule of thumb. I was intending to refit the same belts but using a lower frequency than the as-new setting but the degradation is intimidating me a bit for what seems to be a low mileage / short service interval.
If folks are going to use an Ipod (or their phone) then I would suggest they sample a known tone (near the 100 hz region) to see what their Ipod reads before entrusting their multi thousand dollar motor to it.
I would also recommend you email Ca-Cycleworks, Chris and his crew are the most straight up folks you will ever do business with (other than me ;-).
Thanks,
M./
Michael Heth
mheth@motolectric.com
(415) 992-7840
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