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I've tried software on both my pc and phone to use the frequency analysis method of checking timing belt tension. I'd really like to start using that process rather than my Krikkit gauge, but I can't seem to get results consistent enough to give me confidence. I'm sure the problem is my technique.

Would Tim, Travis, or some of the other folks who feel they've got a process that's reliable please share a few details of exactly how to get good results. Phone mic vs. plug in line mic? How close to belt? Where to tap and how hard? Software settings? Etc...

That kind of stuff...

Thanks!
 

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I actually took photos of my process last time I did a timing belt, a week ago. just haven't downloaded them from my camera yet. Can do that tonight...

I use the app called "Speedy Spectrum" on my Android phone. Works great for finding the first fundamental frequency of the belt.

https://docs.google.com/open?id=0B2nifoCpaFSfOGJkMjQxMDUtNzk1YS00YjEyLTgyZTAtYmI5NjE4MjgxMmRm&authkey=CO_S1NoE

Engine is cold and at 30deg before top dead center (30 BTDC).

Microphone is placed close to the belt, as close as possible. Reach around the front of the engine and strum the belt in the middle between the intake cam pulley and the oil pump pulley. Strum it like a guitar string, do not let the finger touch the belt after the strum, slip the thumb off quickly with one motion.

This is for cars with the round tooth HTD belts only.

Standard software settings, though make sure to turn on peak hold and enable peak hold overlay. you can zoom in on the screen near 100Hz, but I look at the peak hold number in the upper right of the screen.
 

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Discussion Starter #3
Thanks Travis. That's very helpful. I'm glad you've got pics to add as well. Along with the instructions you've just provided, i'll give it another shot over the next day or two and see what kind of results I get.

Thanks again.
 

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I usually tap the top of the belt gently with the handle of a screwdriver, midway between the intake pulley and aux pulley, while holding the mic just above the belt.
 

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What frequency is the target? Do you have to connect some kind of microphone, or does it use the phone's internal mic?
 

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(Snip)... Would Tim, Travis, or some of the other folks who feel they've got a process that's reliable please share a few details of exactly how to get good results. Phone mic vs. plug in line mic? How close to belt? Where to tap and how hard? Software settings? Etc
Edit... late addition: The frequency response method was specified for the round-tooth HTD timing belt, and Lotus never developed or published a similar spec for the old trapezoidal belt. Frequency response is a function of mass and stiffness, and the trapezoidal belt is both lighter and less stiff than the HTD belt. It's reasonable to expect that the trapezoidal belt will require less tension in the belt for any given frequency response, but how much less I don't know. But I do expect that using the frequency spec on the trapezoidal belt will result in a lower tension than you might be anticipating.

If your software, like TuneIt, allows for set-up changes, narrow the spectrum range to just a little more than the target range. You're shooting for 100-110 Hz, so limit the range to something like 80-130 Hz. For our purpose, everything else is just noise, and eliminating it will produce a cleaner, more repeatable reading.

1) All timing belt tension readings are to be taken midway between the auxiliary & inlet cam pulleys.

2) Cold engine, before it's started for the first time that day. Do NOT attempt to tension the belt on a hot engine.

3) 15° - 25° C (59° - 77° F) ambient temperature

4) Rotate the engine through two complete revolutions.

5) Set the crankshaft to 30° BTDC (NOT to the 0° TDC of the old Borroughs spec). As you approach 30° BTDC, stop without backing up in the least (ie, stop with full tension in the belt). This is where a lot of repeatability errors creep in. At 30° BTDC, the cam pulley timing dots should be toward the center, but NOT aligned... they only align at TDC.

6) Hold the frequency meter/ microphone near the timing belt, midway between the intake and auxilliary. Aim the mic at the belt, and get it reasonably close to the belt. It doesn't have to be "right on it", but certainly less than an inch away. Your meter will tell you what it needs... it will respond or it won't. Certainly not just vaguely in the neighborhood and aimed somewhere else.

7) Tap the belt with a suitable tool (eg, screwdriver), midway between the intake and auxilliary pulleys, sharply but only hard enough to provoke a clear reading on your meter, PC or phone. Harder isn't better once you get a clear reading, but it does risk disturbing the belt's tension. Similarly, don't pluck the belt like a guitar string for fear of disturbing the belt's tension.

8) The frequency response should be 100-110 Hz, COLD. Unofficially, 112 Hz for a new belt being tensioned for the first time, in order to compensate for initial stretch.

9) If necessary, slacken the tensioner clamp bolt and turn the eccentric hub as required to adjust the bleet tension (turn counter-clockwise to increase the tension). Tighten the clamp nut to 34-41 Nm. Rotate the crankshaft through 720° clockwise and re-check the belt's tension.

10) After fitting a NEW cam belt, which may be prone to some initial stretch, it is advisable to re-check the tension at 500 mile intervals until the tension is seen to stabilize.

Regardless of the tension measuring method used (Borroughs or frequency), the Gates Racing Blue timing belts seem to whine at the spec tension. I'm not comfortable just loosening the tension until the belt stops whining, sometimes as low as 80 Borroughs, but conventional wisdom says a belt that whines is too tight. I think we need to gain more experience with the blue belts, but until then, I'm more comfortable with a light whine than I am with a way low tension number... just my humble opinion.

Regards,
Tim Engel
 

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Discussion Starter #10
Thanks for the great pics and detailed responses...I didn't get to it this weekend but I'll take another crack at it over the next few days with all the feedback and see if I can get better results.

Thanks again!
 

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Nice post! I was curious if anyone had pictures of a v8 with the belts on like that? Is the target frequency the same on a v8?
 

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The V8 requires the use of a degree wheel and pointer, plus a special crank alignment/ locking pin to get it all zero'd in correctly. Without getting into that full process, I'll just say once the degree wheel is properly set up:

Set the crank to 90 ATDC -- Check Left hand cam belt's Freq. Response
Set the crank to 135 ATDC - Check Right hand cam belt's Freq. Response
Frequency Response for each cam belt = 95 -120 Hz

If the frequency is out of spec, then actually adjusting the belt's tension requires yet another special pin-spanner tool.

Regards,
Tim Engel
 

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Bringing up a year old post, anyone have any more info on the Gates Blue belt?

Regardless of the tension measuring method used (Borroughs or frequency), the Gates Racing Blue timing belts seem to whine at the spec tension. I'm not comfortable just loosening the tension until the belt stops whining, sometimes as low as 80 Borroughs, but conventional wisdom says a belt that whines is too tight. I think we need to gain more experience with the blue belts, but until then, I'm more comfortable with a light whine than I am with a way low tension number... just my humble opinion.
 

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I settled on a repeatable 103MHZ +/- 1.5 MHZ when tensioning my broken-in (1500 mile) blue Gates belt.

I used a free app for the IPhone called EPIC GUITAR TUNER.
 

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Atwell,

Any whine at 103? And since you say it's well broken-in, did it whine initially?

103 is still in the specified range, just the lower third.

Does all this mean you have the Esprit back on the road again?

Of course, I presume you meant Hz, not MHz.
;-)

Regards,
Tim Engel
 

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^^ Car is not yet put back together after the engine/trans removal. Patience. :sad:



Yes, I aimed for the lower end of the tension range because the belt was "broken in".

There was no whine at all before removal. At that time, my "guide", Jim C, who has rebuilt several Esprit engines, felt the blue belt (via twist) and commented "that was kinda loose". He never used a blue belt, though.

He seemed satisfied with the tension after reassembly.


+++++++++

Yeah, I mean HERTZ not MEGA hertz, Ooops. When you use an app that is EPIC you expect more... :crazyeyes
You just look at the numbers, not the scale once it's set up.
 

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Bringing up a year old post, anyone have any more info on the Gates Blue belt?
I asked in a separate thread if anyone has exceeded 50K miles (a number discussed as an informal and UNTESTED recommendation) on a Gates blue belt. No one has replied on that number yet.

My Gates blue belt (installed Oct 2011) has nearly 24K miles in 24 months (88 Esprit). I've yet to run across anyone that has reached 50K miles on a blue belt. My mechanic used the 'official' Gates sonic tool to adjust the belt - I never heard any whining, but it could just be my bad hearing. Belt tension was checked at 18K miles and deemed OK.
 

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Edit... late addition: The frequency response method was specified for the round-tooth HTD timing belt, and Lotus never developed or published a similar spec for the old trapezoidal belt. Frequency response is a function of mass and stiffness, and the trapezoidal belt is both lighter and less stiff than the HTD belt. It's reasonable to expect that the trapezoidal belt will require less tension in the belt for any given frequency response, but how much less I don't know. But I do expect that using the frequency spec on the trapezoidal belt will result in a lower tension than you might be anticipating.
Similarly, the JAE Blue Belt is heavier, more stiff, and marginally thicker than the black HTD belt for which the Lotus frequency spec applies. There is no frequency (Hz) specified for the Blue Belt. If you do tension the Blue Belt using the HTD belt's frequency spec, the tension will be too high.

The softer and more flexible something is, the less the force that will result from a given amount of stretch. The later HTD timing belt is stiffer than the early trapezoidal belt. So, when tensioning, the HTD will seem more touchie, more sensitive to the smallest adjustment made at the tensioner bearing's eccentric. The JAE Blue Belt is even more stiff than the HTD, and it is even more sensitive to small adjustments. Big movements are out, think pressure more than movement. Micro adjust.

Regards,
Tim Engel
 
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