Measure your BELTS Our Mission: To offer quality custom components for the repair/restoration of antique and vintage electronic devices! Site Created 08/10/96 Page Updated 03/30/11   NOW available pioneer CT-93, Nakamichi BX-300 Belt KIT, and the RT-707 LED lighting KIT Vintage Belt KITS      Capacitors!    Dial Lamps

Welcome to the Belt measurement Class 101!

SQUARE BELTS - FLAT BELTS - IDLER TIRES - Broken/missing BELTS

I get many emails asking for certain belts for specific decks. I dont have a backwards compatibility list. No one does! It seems like there are thousands of way to measure these belts too. Between measurements and deck types we have millions of possibilities.

SO! I decided to write a self help web page. This way if you need a belt you can send the dimensions to me. Takes all the guess work out, and helps insure that you get the correct belt. Please see the price list below. You will have to make your own measurements then email me with your needs. I will in turn send you an invoice, or a Paypal payment request. Its up to you.

SQUARE BELTS! (same dimension on all four sides)

1) Refer to the ruler below to acquire the first dimension: Use two pencils to hold the belt across the ruler but, DO NOT STRETCH the belt as you measure it! This is very important.

2) Measure and record the belts length. In this example the belt measures 6 inches.

3) Calculate the belts Inside Diameter. Measured results (6") = (6" X 2) = 12" All we need to do is double your measurment.

4) Then you need to subtract 10% to compensate for stretching, and use of the old belt. 12" X 0.10 = 1.2" Now we take 12" 1.2" = 10.8"

5) We now realize we need a 10.8" belt minimum. We could use any belt between 10.8 and 11.5 assuming the measurement was accurate.

6) Since we have a square belt, then we need to measure that too.

7) If you have a caliper, then this would be the best way to measure. Dont worry to much about measuring them though. We can use common business cards. Each card is approximatly 0.015" thick. So you need at least two because they don't make belts that small. I would start with four cards though. Stack up the cards until they are at the same height as your belt. Use a flat surface, and press down on the cards while measuring!  Then multiply the number of cards used. So if your belt is as high as three cards, then the formula would look like this 3 x 0.015 = 0.045 So now we have the second dimension. (10.8 X .045 square).

8) Thats all we need to determine the size square belt you may need.

FLAT BELTS!

10) We measure and record the belt diameter exactly the same as step 2. In this example the belt measures 6 inches, B but we know to double this. The actual dimension is 12".

11) Once again we make the same adjustment we did in step 4. Take out 10%. Our new dimension for this example is 10.8"ID.

12) One major difference with a flat belt is an added dimension. We already measured the length, now we need the thickness and the width.

13) Lets start with the thickness: Use the same bussiness cards and the same methode we used in step 7. So now we have two dimentsions.

14) Lets get the final dimension (width): This can be measured with a ruler. Just measure across the flat surface.

IDLER TIRES?

Use what we learnt and the instruction below.

MISSING or BROKEN?

We sometimes find the belt is broken, missing, even melted down to a black goo. In this case we want to use string and install it as you would the original belt. Wrap it around the pulleys and wheels as the original would be, then tie it snug in place. The string needs to be a stiff type that does not stretch. Dial cord would be a good example, but cotton thread will work too. Next remove the string and measure it as shown below.

Measure LENGTH

1) Refer to the ruler below to acquire the first dimension: Use two pencils to hold the belt across the ruler.

2) Measure and record the belts length. In this example the belt measures 6 inches.

3) Calculate the belts Inside Diameter. Measured results (6") = (6" X 2) = 12" All we need to do is double your measurment.

4) Then you need to subtract 10% to compensate for stretching, and use of the old belt. 12" X 0.10 = 1.2" Now we take 12" 1.2" = 10.8"

5) We now realize we need a 10.8" belt minimum. We could use any belt between 10.8 and 11.5 assuming the measurement was accurate.

We also have a couple other measurments to be concerned about. If this is a flat belt, then we need two other dimensions. If there is any of the original belt left then this is easy. Just measure it. If there in no belt then we have to measure other parts of the deck and estimate. If we have a square belt then there is only one more dimension we need to figure out.

Flat belts: If you have a flat belt then it needs to run off a pulley and ride a flat surface or two. So try these thing to figure it out, and measure the width.

Measure WIDTH

1) Chances are, the original belt has left rubber markings on the flat surfaces it ran over. For example the flywheel. Measure it and take away about 10%. The same goes for the pulley. See the figure below.

2) In my experiance the flat belt will use about about half of the motor pulley's surface. No matter what! The belt has to be smaller then the surface space on the pulley. See figure below.

If we put the last two statements together we have the motor pulley and the flywheel. So, to recap the belt width must be approx one half the motor pully. It also has to be smaller than the item(s) it turns, (flywheel) in this case. The figure below shows what this means.

Measure THICKNESS

If you have a peice of the belt then a caliper would be the best way to measure. Dont worry to much about measuring them though. We can use common business cards. Each card is approximatly 0.015" thick. So you need at least two because they don't make belts that small. I would start with four cards though. Stack up the cards until they are at the same height as your belt. Use a flat surface, and press down on the cards while measuring!  Then multiply the number of cards used. So if your belt is as high as three cards, then the formula would look like this 3 x 0.015 = 0.045 So now we have the second dimension. (10.8 X .045 square).

If you do not have the belt then we must use experiance here.

1) 99% of cassette decks, 8-tracks, VCRS, and other types of smaller equipment use the standard 0.025" thick belts. This includes turn tables.

2) If you have a good reel to reel deck, then chances are the belt will be thicker. It could be as thick as 0.065". I would probably go with a 0.050" belt for good measure.

Measure a square belt! (same dimension on all four sides)

We sometimes find the belt is broken, missing, even melted down to a black goo. In this case we want to use string and install it as you would the original belt. Wrap it around the pulleys and wheels as the original would be, then tie it snug in place, but not tight. The string needs to be a stiff type that does not stretch. Dial cord would be a good example, but cotton thread will work too. Next remove the string and measure it as shown below.

Measure LENGTH

1) Refer to the ruler below to acquire the first dimension: Use two pencils to hold the string across the ruler.

2) Measure and record the belts length. In this example the belt measures 6 inches.

3) Calculate the belts Inside Diameter. Measured results (6") = (6" X 2) = 12" All we need to do is double your measurment.

Measure HEIGHT

This is a square belt so the height and width should be the same. As shown in the figure below.

This may be a little tricky, but most square belts for tape decks are between .030 and .050 inches anyway. The best way to approximate this dimension would be to measure the depth of the wheel the belt rides on. The figure below shows you where to measure. The hard part is physically taking the measurment. A metal scale will work, or a caliper with the depth gauge. You can stick a business card in the crevis and draw a line where the top of the wheel stops. Then measure it outside the deck. Again keep in mind most of them are between .030 and .050" so use this information as part of your approximation.

Once you have a number, the belt dimension needs to be smaller than your measured number. Now we want to calculate and subtract about 15%. Then you need to find the standard dimension for the calculated dimension. The table below shows a few examples. In the end the belt needs to ride inside the pulley as shown.

 -15% Standard Measured Calculated Dimension TYPE 0.065 0.055 .046-.050 SBS 0.049 0.041 .030-.040 SBO