View single post by Esprit2
 Posted: 03-11-2017 02:16 am
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 289
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I was PM'd and asked for a similar Burroughs/ Krikit spec for the black trapezoidal tooth belt. I thought others might find the info useful, so here's what I replied:

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With the Burroughs BT-33-86J or the BT-33-73F, set a new black trapezoidal tooth belt's tension a little high, at 100 (55 Krikit KR-1), to allow for initial stretch. After 500-1000 miles, the belt will have taken an initial stretch, and the tension will end up about where it's supposed to be for normal running... around 95

Then for routine checking and re-tensioning of a used belt, set the tension to the normal running spec of 95 Burroughs (52.25 Krikit). Lotus experimented through the years, started at 90 (too low), went as high as 105 (too high), and eventually settled at 95. It's a good tension value with a proven track record.

Neither gauge has great resolution, so the two-place decimal is just a matter of doing the math. Don't worry about trying to get anything closer than a round number... plus or minus. Personally, I'd rather err a little on the plus side. Anything over 105 Burroughs (58 Krikit) will cause a black belt to whine, and any belt that whines is too tight.

When you do a routine tension check, anything down to 90 Burroughs (49.5 Krikit KR-1) is acceptable. 90 is not "good", and 95 is better... but it's not "bad". Any lower than 90, and you should re-tension the belt as soon as possible.

At 80 Burroughs (44 Krikit KR-1), count your lucky stars and don't even put the keys in the ignition. That's scary loose.

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The values given above apply to both the black HTD round tooth belt and the black trapezoidal tooth belt. The trapezoidal belt is supposed to run with more tension than the HTD belt. However, the Burroughs gauge is thickness sensitive, and the HTD belt is thicker than the trapezoidal belt. The end result is that the trapezoidal belt ends up tensioned as the Burroughs gauge says it is (95), and the HTD belt ends up a few pounds lower... where it should be. It works without the need to calibrate another gauge, and it's easier to remember one tension spec for both black belts.

The blue Gates Racing belts are another story. The tension for the blue HTD belt was discussed previously, and that's been worked out through owner experience over on the TurboEsprit list on YahooGroups. There is no offical factory tension spec for the blue HTD from either Gates or Lotus. This is all grassroots.

The blue trapezoidal belt is relatively new on the market, and I'm not aware of an established tension yet. Expect it to be a few pounds lower than the standard black trapezoidal belt tension. For starters, we're setting the tension just below (~comfortably below) the "whine threshhold". Sorry, I don't have an established number for you yet. If you use a blue trapezoidal belt, report your results so we can all learn from your experience. We'll add it to the collective experience/ knowledge base.

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IMHO, the tension spec given in the JH Workshop Manual is too low. Finding a Kent-Moore KM-128 gauge might be difficult enough to keep anyone from using that tension spec, but the tension that results is too low. I won't recommend using it.

Regards,
Tim Engel

Last edited on 03-11-2017 02:21 am by Esprit2