View single post by Esprit2
 Posted: 03-15-2017 07:28 pm
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 341
Rick in Miami wrote:
I did set the tension cold @ 47# with a Krikit.
Okay, good. I'm with you there.

Rick in Miami wrote:
I included calculated hot specs only because they had been included in the T104 tension specs.
My concern was that it sounds to me like you're giving the hot tension too much credibility as a "Spec". It's not. There is no hot spec in terms of something with real value/ worth. If you properly set the tension cold, then allow the engine to warm up fully and measure the tension again, the hot tension you get is the result of your good procedure. In a cause and effect relation ship, hot tension is the effect, not the cause. Doing the correct procedure well, then gaining confidence in your work because it produced the "correct" hot result is bogus thinking. You're giving credibility to the hot result like it's the god given end goal. It's not. And it's not reliable. Purge if from your thinking as "something to attain".

What you're stating is like taking poison after the fact in order to bolster your confidence that you took the right blood pressure medicine this morning. There's something wrong with that.

Rick in Miami wrote:
The twisting & deflection test comparisons were done to reinforce that I was in the ballpark.
Again, that's backwards. The twist & deflection test are not foundational. They're grassroots tricks that 'might' give ball park results if performed by someone with a practiced feel; but for an untrained first timer, the results are unreliable. The gauge measurement reinforces that you might have developed a practiced feel for the twist test... and frankly, I discount the deflection test as stated. But neither the twist nor deflection tests should be considered standards of correctness for any gauge.

Also, the twist and deflection test results vary dramatically with the stiffness of the belt. And the Gates Racing blue T104RB is thicker, and significantly stiffer than the old, black, HCR trapezoidal tooth belt. Twist test results for the blue belt (once they're developed) will be considerably different from those for the black belt. Don't mix them up.

Rick in Miami wrote:
I am open to more hands-on experience and recommendations but since none had been offered to this point I wanted to share mine.
Thanks for sharing the results of what you're doing, and please don't get the feeling that I'm beating you about the head and shoulders. We do need to collect that sort of data to zero in on a good tension setting for the T104RB blue belt, and I appreciate your contribution. I'm just trying to curb the spread of some common mis-information along the way.

If you, or anyone, have the time and the inclination, it would also be helpful to know what happens as the tension is increased in small steps. At what initial cold tension does the belt begin to whine when the engine gets hot? And at what cold tension does the belt begin to whine right away... cold? Those are upper limits we need to avoid, but yet approach. Staying too low just out of fear of reaching an unknown whine threshhold isn't good... too low tension is hazardous. But how high can we go without provoking a whine. So far, I've not read of anyone sneaking up on those tension values for the T104RB. At least not in a statistically meaningful sample... more than one incidence. Much of that work has been done for the round-tooth HTD blue belt. And the recommended Burroughs tension for the blue HTD is in that 82-84 cold range (I use 83-84, but that's splitting hairs).

In your previous message, you wrote that you used the Burroughs/ Krikit conversion factor of 55%, and the recommended Burroughs values "FOR THE T104RB" to get to a target setting of 47 lbs cold. Where did you find the recommended Burroughs setting for the T104RB? The value you used matches what many are using for the round-tooth HTD blue belt. It would be convenient if the same value also turned out to be the best tension to use for the blue trapezoidal T104RB as well, but I haven't heard any definitive results that support that. I'm not contesting that tension for the T104RB. It's just that if there's more information on that posted somewhere, I'd really like to read it and learn. Point me to it.

The trapezoidal belt's shallow tooth engagement requires higher tension to maintain a secure bite on the pulley, and to not jump timing. The HTD belt's deeper tooth has a better mechanical bite, and can run with lower tension. I previously mentioned that the Burroughs gauge is thickness sensitive, and the round-tooth HTD belt is thicker than the trapezoidal tooth belt. With that in mind, Lotus recommends 95 on the Burroughs for both belts, and the thickness differences result is a lower actual tension in the HTD belt than in the trapezoidal belt.

Maybe that's what we'll confirm for the blue belts as well. If 82-84 Burroughs works well for the blue HTD, then perhaps it will also provide the adequately higher tension for the blue trapezoidal belt by virtue of it's thinner section producing a higher Burroughs reading.

The paranoid concern is that the tension is lower... 82-84 vs 95. And historically, low tension has not worked well for trapezoidal belts. The trapezoidal belt has a long, early history of jumped timing and bent valves. It has long been shown that the trapezoidal black belt needs all the tension it can get, short of provoking a whine, so there's some fear/ reluctance at work in the search for a new 'lower' tension for the blue T104RB. How low is too low?

Myself, I'd rather start high, discover the belt whines when hot, and work my way down to a lower setting that doesn't provoke a whine. I'm fearful of just blindly dialing in a quiet low tension, then waiting to see if it jumps timing down the road. Unfortunately, each trial requires letting the engine cool down over night, so only one trial per day will drag out any testing. And it would be nice to test a number of belts on a number of engines. One is not statistically meaningful.

Technically, the blue belt is a worthwhile improvement. We just need to learn how to use it without bending anyone's valves in the process. Hot tension, twist, and deflection tests are not safe ways to get there. 'Maybe' we back into blue belt versions of the hot, twist & deflection "specs" later, after we've first determined a viable cold tension by using good gauges.

I don't mean to just stand on the sidelines and point. But I have an unheated garage, and for now it's still cold here in Minnesota. Plus, the engines I have access to right now have HTD belts & pulleys. I'll jump into the game as soon as I can.

Long winded again... sorry about the bandwidth.

Tim Engel

Last edited on 03-16-2017 10:37 pm by Esprit2