Timing belt tensioning with a Snark - LotusTalk - The Lotus Cars Community
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post #1 of 4 (permalink) Old 07-16-2019, 06:47 AM Thread Starter
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Timing belt tensioning with a Snark

Having just installed a new timing belt on my '87 Turbo Esprit, I was confronted with the usual dilemma of setting the tension.

I've seen the posts about the newer method of using resonant frequency, along with suggestions regarding microphones and guitar tuners. ...but then I remembered that my wife plays harp and uses a Snark to tune it.

For those that aren't familiar with them, a Snark is a device for tuning stringed instruments, and are available from Amazon for ~$15.00.

The tension specs for the 4-cylinder Esprits call for a frequency of between 100 and 110 Hz on a cool engine, measured between the cam and distributor drive sprockets.

The frequencies of the musical notes in that range are:

G = 98.00 Hz
G# = 103.83 Hz
A = 110.00 Hz

I wasn't sure if the Snark would be sensitive enough to detect a "plucked" timing belt, but it worked beautifully.

Set to "microphone" (as opposed to "vibration") I held it about an inch from the belt and you can see the results in the video:



Newer Snarks include a frequency readout as well as the musical note, so I'll be buying one of
my own to keep in my toolbox.

-Doug

1987 Turbo Esprit
1965 Seven
1963 Elite (The works twin cam)
Erik L and Jenna'sEspritTurbo like this.
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post #2 of 4 (permalink) Old 07-16-2019, 10:00 PM
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I drove my late 88 Epsrit with 2 Gates timing belt 50K miles/49 months - the mechanics used a simple twist method for tensioning. I realize some are not comfortable with a seemingly informal process, but it's difficult to argue with 50K miles with this process.

Here's the video I posted showing the tension (taken about 2K miles after installation).


Eddie B
87 Esprit 'SLEEK GT'
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post #3 of 4 (permalink) Old 07-17-2019, 06:45 PM
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Some mechanics also have a "calibrated elbow" instead of a torque wrench. If you have enough experience and are comfortable taking short cuts you can get away without using sophisticated test equipment. Torque wrenches and vibration meters are meant to standardize these procedures so even an inexperienced tech can do them reliably. Bottom line, if you go to an experienced tech, someone intimately familiar with Lotus's and has done this more than a few times, you can use the twist method.
David Teitelbaum
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post #4 of 4 (permalink) Old 07-22-2019, 07:28 AM
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Quote:
Originally Posted by Lotuar View Post
(Snip)... The tension specs for the 4-cylinder Esprits call for a frequency of between 100 and 110 Hz on a cool engine, measured between the cam and distributor drive sprockets.
It's important to keep in mind that the frequency method requires setting the crank to 30 BTDC, not TDC as will the older Burroughs gauge "pounds" of tension method. Using the frequency method at TDC will produce the wrong tension.

The Lotus Frequency spec only applies to the black HTD round-tooth timing belt. Specifically, the B-Prefix, HSN belt; however, there's little difference/ error with the earlier A-prefix HCR belt.

There is no Lotus frequency spec for either the older trapezoidal tooth belt, or any Gates blue belt. But if your 9XX has a black HTD round tooth belt, this Snark stringed instrument tuner sounds like an interesting option.

Regards,
Tim Engel
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