Cam Belt Tension with Clavis Gauge

[Brandt]

Hi Everyone

Is there a specification for adjusting the trapeziodal cam belt using a Clavis Gauge? Can the round tooth belt specification be used?

Kind regards

Brandt

[ralphw]

Brandt

The Burroughs Gauge setting for the later belt is 95 Units COLD. If this is the same as the trap belt, then the clavis frequency should be the same. I havent worked it out but there were some discussions about this some time ago and I think the later belt was set at 110Hz at Ambient temp.

Cheers

Ralph

[fjmuurling]

Here is a link http://www.lotusespritworld.com/EGuides/ET...l/Cambelts.html , scroll down wheer the correct procedure is described. (engine has to be set 30 deg BTC).

Freek

Oeps just reread the text and the procedure is only for the engines with the HTD (rounded tooth profile belt).

Freek

Edited January 6, 2009 by fjmuurling

[910Esprit]

Here is a link http://www.lotusespritworld.com/EGuides/ET...l/Cambelts.html , scroll down wheer the correct procedure is described. (engine has to be set 30 deg BTC).

Freek

Oeps just reread the text and the procedure is only for the engines with the HTD (rounded tooth profile belt).

Freek

The way I read it is that a Clavis Gauge is recommended for all HTD belts. (Not that it can't be used for square profile belts). I use the same procedure for my square belt and am happy with the results.

cheers Steve

[eengel1]

Hi

Note that the belt tension measurement has also been discussed in the thread

"Cambelt tension gauge, to borrow / hire?"

http://www.lotusespritforum.com/forums/ind...showtopic=20107

Now I don't know if my belt has a round or a square tooth profile.

I do not see any reason why the tooth profile should affect the belt tension, unless the belt itself is different.

Do they pulleys also change with belt tooth profile ?

Cheers

Marc

[910Esprit]

Marc

Unless it has been changed, your car has a 'square' profile teeth. The round teeth cooincided with the HC engine, which was introduced around 87?

Yes, the pulleys are all different (but tension the same I think)

cheers Steve

[ralphw]

If the tension is the same eg the square tooth belt and the HTD belt both have a Burroughs gauge setting of 95 units then the Clavis frequency will be similar for both belts. There is no reason why the Clavis gauge cant be used in both applications.

The relationship between belt tension (T) and frequency of vibration (F) may be calculated from knowing the mass per unit length of the belt (M), and the belt span (L), using the expression;

T=4ML

[Brandt]

Hi Everyone

Ralph, I also saw the formula, and I assumed all of the variables are pretty much the same for the HTD belt and the trapezoidal belt, except I was unsure on the weight of the belts (M in the formula).

Does anyone have the weight of a HTD belt for me?

Iv'e adjusted the belt tension using the 90

[ralphw]

Brandt

That one is easy. Weigh each belt. The tooth pitch is 9.525mm so the number of teeth multiplied by 9.525 equals the belt length in millimetres. Divide by 1000 to put it into metres.

Divide the weight of the belt by the length and you will get M (kg/metre). If they are the same or similar assume 110hz if not adjust it up or down in proportion to the difference as it is a linear factor in the equation eg if the difference is 10% then it will be 110*0.9 = 99hz or 110 *1.1 =121hz depending on which one is heavier.

Chances are the difference will be much less than 10% but I havent got examples of the 2 belts to measure and tell you.

To 90

[eengel1]

hi can somebody post this link again pls

http://www.lotusespritworld.com/EGuides/ET...l/Cambelts.html

can't open or find it

merci

Marc

[910Esprit]

hi can somebody post this link again pls

http://www.lotusespritworld.com/EGuides/ET...l/Cambelts.html

can't open or find it

merci

Marc

You can find it in the 'for sale' section! Look for the fairly recent thread wanting to borrow a burroughs gauge

[fjmuurling]

Here is a link Cambelttension with Clavis Gauge , scroll down wheer the correct procedure is described. (engine has to be set 30 deg BTC).

Freek

Oeps just reread the text and the procedure is only for the engines with the HTD (rounded tooth profile belt).

Freek

Corrected the link (I had the description and the url mixed up)

Freek

Edited January 8, 2009 by fjmuurling

[ralphw]

Brandt

I havent got the two belts to compare the weight, but a quick check through numerous Gates applications catalogs and a bit of guestimation I would say that you would expect the Clavis to be in the region of 116Hz assuming the link you have been quoted recommend the HTD belt to be 110 hz (I think it does from memory). You wont get it spot on but aim to be in the 110Hz to 120Hz region. If it drops below 100Hz then readjust.

Cheers

Ralph

[Brandt]

Hi Ralph

I'm guessing that the HTD belt is slightly heavier than the trapezoidal belt, which means that the trapezoidal belt should have a slightly higher frequency than the HTD belt. What you

[eengel1]

thanks for the link

I'll have another look.

Cheers

Marc

[ralphw]

Hi Brandt

Not bad, 10% error. As I said before aim between 110 and 120Hz. You are right, the HTD has bigger teeth so is slightly heavier. Cant remember if you engine has an Autotensioner or not, think it does. If not ensure that you check the tension regularly as with fixed tensioners the tension is only correct on the day they were set and as they get looser more damage occurs, bit like a tow rope. The autotensioner is not always liked by everyone but its ability to keep the belt at the correct tension will give much more reliable service from the belt over time.

I have just remembered that I have a Trap belt somewhere from my Sunbeam Lotus so when I get round to doing my belt on the Esprit, an HTD, I will weigh them and accurately recalc the frequency for the Trap belt.

Regards

Ralph

[910Esprit]

Another informative link:

http://www.espritfactfile.com/timingbelt2.html

[eengel1]

Hi

Have a spare belt

Trapezoidal tooth profile ref A907E0191Z

Measured weight :142g

Now someone else may have the weight of the round tooth profile belt, we can do the math then.

Cheers

Marc

the attached a chart shows the Clavis freq. of the square toothed belt (Hz) as function of the round toothed belt weight (g) , based in Ralf's formula

Difference in frequency between the two belt types should be small .

example : 13g give around 5Hz diff

Cheers

Marc

[910Esprit]

Marc

Good info. For completeness, would it be possible also plot the frequency as imperial Lbs tension? (I think Lotus 'units' map to Lbs unless anyone can show me otherwise.

cheers Steve

[ralphw]

HI,

anyway the HTD belt weight is 154 Gr.

Cheers

Giorgio

From the above lifted from the Stevens Technical Room (Thanks Georgio) some simple mental arithmatic suggests that the tension for the Trap belt is 114.55Hz

eg 4*142*L(trap)

Edited January 16, 2009 by ralph

[eengel1]

Ralph

Think 114Hz is correct, I got the same result.

Thanks for providing the weight of the HTD belt.

Steve

for plotting the freq as function of tension I need the free length of the belt and the total length.

I'll have to measure those. Frequency changes with square root of tension.

Do you know what the Burroughs gage units are?

Cheers

Marc

[ralphw]

Marc

tooth pitch is 9.525mm times the number of teeth. Can never remember but I think the number of teeth is 133

Cheers

Ralph

PS I think the Burroughs gauge should show 95 units

Edited January 19, 2009 by ralph

[slewthy]

Just tried tuneit with the mic that came with my PC. My trapezoidal belt read a consistent 114.3Hz . Reassuring!

Took 1 min to download program, 1 min to install and 1 min to test. Brilliant!

Of course, cant avoid replacing the belt etc etc but this gives some confidence that the current one is at the right tension at least.

[The Real Stig]

iAnalyzer app is used by Ducati home mechanics to test the cam belt tension.

 

In theory you could use this in stead of the more expensive and rare Borroughs tool.

 

From calculations above the tension at 30° TDC should be 115 Hz.

 

Can anyone verfy this by comparison?