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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
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Is the tension the same for the rectangular and the later Lotus half-moon belts?Pete,
Sorry about keeping you waiting... I'm not a regular here.
Short answer: Yes, for all practical purposes, but it's not apples to apples.
The official Lotus gauge was the Burroughs BT-33-86J, which is sensitive to belt thickness. Thicker belts give higher readings, and the HTD/ round-tooth belt is thicker than the trapezoidal tooth belt.
As Lotus gained experience with the trapezoidal tooth belt, they kept playing with the tension spec... 90 Burroughs to begin with, then 95-105 (100+ is too high), then finally 90-95. 95 is in the middle of all that, and the value I have used with satisfactory results for decades.
When Lotus switched to the HTD belt, they didn't issue a new gauge, or re-calibrate the old one for the new thickness. They recommended tensioning the HTD to 95 on the old gauge, but the result would have really been something a bit lower... in the 90+ range somewhere. So both belt types are playing in the same general tension area.
After playing with both belt styles for a lot of years, I've settled on the same tension for both:
100 for a new belt to allow for initial stretch.
95 when re-tensioning a used belt that's broken in.
Experience showed that a new belt would lose about 3-5 lbs of tension in about the first 1000-1500 miles... after the initial stretch settles down. Rather than have to re-tension every new belt at that point, I just dialed in that much extra to begin with. I still check every new belt's tension in 500 mile increments until it's tension settles down, but it rarely requires adjustment if I start at 100 Burroughs/ 55 Krikit.
The Krikit conversion factor came about over time by tensioning many belts with a Burroughs, then cross-checking it with a Krikit. The KR1 always produced number values that are about 55% of the Burroughs values. The rest of the values I posted near the end of the 8th post, above, are based upon my experience/ opinion, and are not Lotus specs.
The J-H tension spec (3 1/2 on the KM-128 = 35 Kilopond = 77.2 lbs-force) may be low, and I don't recommend following it until that can be confirmed. I don't know exactly what characteristic the KM-128 measures, or if 77.2 on the KM is anything like 95 on the Burroughs. I won't even crank a 907 over if the belt tension is under 80 Burroughs; and as a number, 77 just makes my skin crawl when used in the same sentence with, "907 timing belt". But again, I don't know how number values correlate between the KM-128 and Burroughs BT-33-86J (I don't own a KM-128).
Having said all that about low tension values, JAE has worked with Gates Racing to develop an HTD belt that uses current technology HNBR rubber. The belt is BLUE, thicker yet, stiffer, and responds differently to all of the factory specified gauges. At 95 Burroughs, it whines, a sign that a belt is too tight. The tension has to be dropped down to 80 Burroughs before the whine subsides. At that point there's still a slight whisper, but I give in to my old bias and won't go below 80. Call it superstition.
Last edited on 05-28-2014 08:43 pm by Esprit2