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fjmuurling

Cambelt Tension

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Hello,

Last week i performed some maintenance on my car and the cambelttension needed to be checked (replaced it about 1000 km ago). The initial method I used to tension the belt was the twist and turn one but I never felt really happy with it. So I went looking for a burrough's gauge without results. After an email to Lotus (very quick reply) I got an pdf file with a new method of tensioning the cambelt on 4 cylinder engines, it meant using a clavis gauge which is very expensive (around 600 pounds). A gates SST 1 does the dame job as the clavis gauge but doesn't display the frequency and still costs around 400 euro.

After reading some posts in the V8 section I came across a piece of tuner software for musical instruments. I bought a good microphone, downloaded the software and installed it on my Laptop and guess what it worked great (see the attached pictures).

The program is called Tune!It 3.40 and the microphone I used is one from Trust, and of course you need a Laptop or Computer with a soundcard.

See the attached pdf file on how to tension the belt.

To make a long story short I just wanted to share this information with all of you and I hope you find it usefull.

sn_ef_p18a.pdf

post-721-1222969583.jpgpost-721-1222969568.jpg

Freek

Edited by fjmuurling

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Interesting. Did you notice any difference in the tension from your twist method and sound of the belt with the engine running? Can you correlate the setting against a guage, if not the Burrough's maybe another eg Kriket?

Edited by DanR1201

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I have don't the burroughs gauge and i tried to order the kriket one about 5 months ago at my local gates dealer but without result, so i can't compare it for you.

The initial setting was performed (when fitting a new belt) by means of twisting the belt (a little bit less than 90 deg.) between the inletcam and the aux cam. When checking the belt after aprox 1000 km the frequency was about 73 Hz. which was too low, however in order to set the belt tension on spec again a marginal tightening of the cambelt tensioner was needed. It took me about 8 times of getting under the car and getting back up again.

The distance from the belt to the microphone was about 7 mm and almost in the middle between the two sprockets. The belt was only lightly tapped by means of socket head screwdriver.

As for the sound i know a properly adjusted belt has to "sing"a little bit when running but i didn't notice it maybe it is because i don't know what to listen for. All I can tell is that the whole seems to run better and smoother.

Freek

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I have don't the burroughs gauge and i tried to order the kriket one about 5 months ago at my local gates dealer but without result, so i can't compare it for you.

The initial setting was performed (when fitting a new belt) by means of twisting the belt (a little bit less than 90 deg.) between the inletcam and the aux cam. When checking the belt after aprox 1000 km the frequency was about 73 Hz. which was too low, however in order to set the belt tension on spec again a marginal tightening of the cambelt tensioner was needed. It took me about 8 times of getting under the car and getting back up again.

The distance from the belt to the microphone was about 7 mm and almost in the middle between the two sprockets. The belt was only lightly tapped by means of socket head screwdriver.

As for the sound i know a properly adjusted belt has to "sing"a little bit when running but i didn't notice it maybe it is because i don't know what to listen for. All I can tell is that the whole seems to run better and smoother.

Freek

I've been looking at the Tune-it and a cheap microphone on a PC for a bit too. I plan on comparing that setup to a Laser Doppler Vibrometer and a digital oscilliscope here at my work. We'll see how accurate it is, hopefully fine, cause I want to do it that way too.

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Don'nt use a very cheap microphone, it needs to be sensitive and able to detect low frequencies. Mine costed a bit less than 20 euro.

Freek

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I borrowed a Burroughs gauge and set the belt tension as advised. Then I took a steel ruler, put it across the belt snubber on the inlet camshaft and the cast boss by the exhaust camshaft, the ruler running along the belt between the cams. Then I used a spring balance to pull the belt up until it just touched the ruler. This gave a pull of 12 to 14 lb for the correctly adjusted belt. Since then, I've always used the spring balance method; last year I changed the belt after 5 years and about 15,000 miles - no signs of wear. I try to change the belt every two years, but it's such a miserable job...

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An important note to anyone attempting this method -- you must turn the engine to 30deg BTDC each time you are to take a measurement, or the frequency reading will be completely wrong! Each time you make a tension adjustment you must rotate the engine at least twice before taking a new reading.

TuneIt! works great, I've even used it with cheapo PC mikes. Make sure you turn the stereo off, though!

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Don'nt use a very cheap microphone, it needs to be sensitive and able to detect low frequencies. Mine costed a bit less than 20 euro.

Freek

I design microphones... To go in the human body.

But the point is I want to verify a particular cheap microphone that everyone could buy from Radioshack. If it doesn't work, it doesn't work.

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THANK YOU! THANK YOU!!! I was looking for proper gauge almost one year without success.

Your idea is briliant and it's working!

RGDS, B

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THANK YOU! THANK YOU!!! I was looking for proper gauge almost one year without success.

Your idea is briliant and it's working!

RGDS, B

Yes it is a good idea, I know Sanj told the turboesprit list about it over a year ago, but I hadn't tried it yet. I will now.

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I will.

<{POST_SNAPBACK}>

So what are you waiting on, you've already had a whole day to do it.

Git R done....... :rolleyes:

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Forget the mike too much trouble. I just purchased a clip-on transducer (about $20 US) designed for tuning instruments, available from dozens of internet merchanges and have every reason to think it will be even better than a mike and simpler to set up. Just clip it to the top run of the belt. My engines apart at the moment so it'll be a week before I can give it a try. Anyone tried that yet?

Hello,

Last week i performed some maintenance on my car and the cambelttension needed to be checked (replaced it about 1000 km ago). The initial method I used to tension the belt was the twist and turn one but I never felt really happy with it. 

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If you clip something on the belt it will change the weight and therefore also the frequency. The frequency depends on the mass of the belt, the free length and the tension.

Freek

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Any chance of uploading the pdf again please? It seems to have gotten lost in the forum upgrade. Thanks.

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

these days I use this procedure, but I use an app on my Android phone called "speedy spectrum" to measure the acoustic resonance.

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Thanks. Now, for the next question, does anyone know what frequency a used (say, 1000 miles plus) belt should vibrate at?

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I have not found a Lotus specification for a used 4 cylinder belt which strikes me as being odd. For a V8, Lotus state a new belt (i.e. less than 500 m / 800 km) is 120 - 135 Hz and a used belt is 95 - 120 Hz. Quite a difference.

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Those numbers for the V8 are correct, and were a service bulletin revision by Lotus dated June 18, 1999. That same bulletin also revised (slightly) the degrees ATDC no. 2 for the LH belt to 80 degrees (previously 90), and RH belt to 120 degrees (previously 135).

The reason given for the revision was "to better allow for new belt bedding and stretch, and to improve measurement consistency, as a result of ongoing data analysis."

Are there really no revisions to the 4-banger?

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Set the tension to the spec in the service manual regardless of new or used. The tension on the belt is specified to ensure there is always load on the belt. When the tension drops too much, then the belt sees load reversals which causes most of the damage. Personally if the belt is off, I would always put a new one on

Cheers

Ralph

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Hi folks, I am new to the forum and new to Lotus ownership. Probably everyone knows this but when you change your cambelt just be careful. The water hose up to the water-pump can easily be cut through by the cam wheel if it is not correctly positioned. The top jubilee clip on this same hose can also foul and damage the waterpump drive belt. Roy.

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