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Discussion Starter #1
So I have my 600mile old ST3, and it is five years old so I am going to replace the belts. The belts came in from LT, and I decided to check the tension as it sits now for a reference point. I thought an easy way to start would be to try the 5mm key method just to see what it feels like. Well I have watched the videos, read all the threads in a variety of forums, and there is no way I can get any hex key under that fixed pulley between it and the belt. On either cylinder. So I must conclude that the belts are extremely tight. Now I have used some software and a usb mic on my laptop to try and get the harmonic twang to get a steady reading, but the numbers fluctuate wildly and it is hard to tell what it really says. Suggestions appreciated.
 

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maybe try the hall of wisdom for the fish scale method. basically you pull a fixed load on the scale and get a fixed belt deflection, record the numbers and then duplicate it with the new belts.
 

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Now I have used some software and a usb mic on my laptop to try and get the harmonic twang to get a steady reading, but the numbers fluctuate wildly and it is hard to tell what it really says. Suggestions appreciated.
Try using software that provides a graphical representation of the sound sample as I have described on my webpage here:

http://home.comcast.net/~mmullen38/Beltadjust.html

It is not the most convenient method but it works well and provides more certainty when you can "see" what you are measuring. Also, make sure the mic is facing one side of the belt or the other instead of being centered on the edge of the belt. That can provide unstable readings because the belt is going back and forth past the mic.
 

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On an ST3 you shouldn't get a 5mm to "go" thats too loose. At 100 to 110 hz on a new belt a 3mm is close. Thats been my experience using a Gates 507c belt harmonics insterment at least.
 

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... I thought an easy way to start would be to try the 5mm key method just to see what it feels like. Well I have watched the videos, read all the threads in a variety of forums, and there is no way I can get any hex key under that fixed pulley between it and the belt. ...
If I understand what you are trying to do then I think you have it wrong. The object is not to fit the 5mm between the belt and the pully. The object is that there should be 5mm of belt deflection on the section between the top 2 pulleys.
 

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If I understand what you are trying to do then I think you have it wrong. The object is not to fit the 5mm between the belt and the pully. The object is that there should be 5mm of belt deflection on the section between the top 2 pulleys.
That would be correct for your 4 valve dual cam motor. Not for the single cam three valve motor in the ST3.

Ducat was correct. 3-4mm gap is close to being correct.
 

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Discussion Starter #7
Well that part was solved using a piece of software to verify that the belts were at about 125 hz rather than 110. Getting the tension correct turned out fine. If that were the only issue I was having things would have been great (see the thread entitled 'belt change screwup' if you are interested).
 

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The belt tension will vary based on the position of the piston. I check mine with the respective cylinder at TDC.

Larry
 
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