View single post by Esprit2
 Posted: 10-15-2016 07:12 am
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 289
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qwerty wrote:
You can also replace the standard belt with a gates racing belt for apparently 3x the life.
Gates Part # T104RB
The Gates Racing blue timing belts are a definite step up in durability. The other plus is that the blue belts are very stable, and it should not be necessary to re-tension the belt for a long time. Continue to check the tension on the normal schedule, but it should rarely be necessary to make a tension adjustment.

The only problem is that Lotus isn't doing any new parts development work on an engine that went out of production approx 36 years ago (907 with trapezoidal belt), and Gates Racing won't make decisions/ specs for another company's product (a Lotus engine). As a result, there is no official tension spec, and no corporate effort to establish one.

There has been a Gates Racing blue belt for the round-tooth HTD belt for several years, and a pretty strong grassroots effort to zero in on a correct tension (mostly on the TurboEsprit list on YahooGroups). At the Lotus tension spec, the blue belt has a pronounced whine, which indicates it is too tight. With a lot of users reporting results, it now appears that 82-84 on a Burroughs gauge is about right for the HTD. But, the Burroughs gauge is thickness sensitive, and the blue HTD is thicker than the old black belts. So while a 'reading' of 82-84 works, I can't say exactly what the actual tension in the belt is. I suspect that it's something in the 90 range, but can't say for certain.

If you really want longer belt life, then the best solution is to convert to HTD pulleys, then go with the Gates Racing blue belt. Still hold the mileage limit down to about 50k miles, but ten years should be reasonable for a time limit.

Short of converting to HTD, the Gates Racing #T104RB blue belt is the best trapezoidal-tooth belt option available, but it's going to take another grassroots effort to zero-in on a consensus tension for it.

Somebody needs to go first. Looks like that's you. I highly recommend that you tension it using a Burroughs gauge so that the data is easier to correlate back to accepted numbers.

Set the tension as tight as possible, short of causing a whine. The belt may not whine on cold start-up, but the tension increases as the engine comes up to temperature. (A OEM black belt set to 90 Burroughs cold will end up at about 125 when the engine is hot.) Since the tension is to be set cold, it's necessary to let the engine cool down over night, then try setting the tension a few pounds lower, and let it warm up again. Repeat as necessary, one tension adjustment per heat cycle.

As I mentioned above, the blue HTD is thicker than the older black HTD belts. The basic web, not the depth of the teeth. Use a vernier to measure the web thickness between two teeth, and report the thickness here. That will be helpful in trying to correlate blue vs black Burroughs readings.

Once the Burroughs tension is determined, it's then possible to correlate a Krikit KR-1 tension reading. On a cold engine, take a fresh reading with a Burroughs. Then take a reading with a Krikit. If you feel energetic, change the Burroughs tension in increments of 5, from around 75 to 100, taking a corresponding Krikit reading as you go. Create a conversion scale.

There's no published math formula that relates Burroughs to Krikit, so empirical measurements is the only way to go. Neither gauge actually measures the tension in the belt. They measure some other attribute, and correlate that back to tension through some formula they're not sharing. Unfortunately, each gauge measures a different attribute, so back to back measurements of the same belt tension is the only way I know of to correlate readings.

Regards,
Tim Engel