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Vittorazi Belt Tension Advice


rob999
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The following is reproduced with the permission of Vittorazi from a conversation I had with them on FaceBook.

It concerns the simple procedure of checking or adjusting the belt tension. The following is a much more comprehensive account of the procedure which is not mentioned in the mortors handbook.

To clarify, the weight on the end of the wrench is 3.5kg suspended from the small hole at the end of the wrench supplied for the purpose.

Vittorazi:

"We are adjusting all the belts with initial values between 3.5 and 4 kgs, taken as a reference the special wrench Vittorazi."

Vittorazi:

"Here in the factory, we have an electronic and expensive instrument ( aprox 500€) for adjusting the belt, which shows the vibrational frequency of the belt.

First, we have to say that all the belts do not have the same structure and elasticity, so this leads to variation of the values of frequency vibrators, applying the same torque. In our studies, we analyzed hundreds of engines with the belts GATES.

In conclusion, with GATES technicians we have established that, fixing a determinated frequency, all the values expressed in Kgs fall in the value of 3.5-4.0 kgs .

We currently recommend :

-For the initial tension apply 4.0 kgs

-For the following readjust apply 3.5kgs

-If the tension applied (3.5kgs) is not sufficient (for a belt slipping) then carrying out the tension to 4.0kgs

-If you have the right electronic tool that analyzes the belt frequencies, always set the belt at 470 Hz.

We are going to publish within the end of the year a new release of the user manual Moster185."

Me, talking to someone else who recommends turning the prop to get an accurate adjustment:

"I think he means turn the prop several times in each direction. I have done this and it makes the spanner tighten up a bit more under its own weight. I have mailed Vittorazi asking for clarification on this point, but as yet nothing forthcoming from them. Vitorazzi Vittoraziday ParamotorFest I wonder if you could clarify, when doing the adjustment, both nuts undone, weight on the wrench, should the prop be turned several times in each direction, OR should a static weight be used with no prop turning ??"

Vittoraziday ParamotorFest:

"During the process of tensioning is important to rotate the pulley (or the propeller connected to the pulley) about 2 turns clockwise and 2 counterclockwise.

This allows a perfect adjustment of the belt grooves in the grooves of the pulleys. This procedure can be done all the times, especially is important when a old belt is replaced with a new one.

This operation must be done when the Vittorazi wrench is inserted, the weight is hanging and of course the eccentric pivot is free to rotate in the hole in the crankcase.

As a result, you will notice a slight lowering of the wrench, just due to this adjustment."

Vittoraziday ParamotorFest !Attention!

"SAFETY ADVICE to all owners of motor Moster185. We know how simple is start this engine. This unique feature, it can also become a danger when you are "playing" with the propeller. So my advice is to disconnect the spark plug cap or switch off the engine by a on/off button where suitable."

Vittoraziday ParamotorFest:

"A simple operation such as adjusting the belt requires several precautions. We always invite the pilots/owners (when possible) to make their requests to experienced and qualified staff, able to perform these operations and dispense tips and updates about the operation of the engine. At your disposal."

Sorry if this witters on a bit, but its advice from the factory that differs from the handbook....may save someone bearings somewhere.

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It is possible to adjust belts by frequency without the expensive kit.

470 Hz is A# above middle C. If you have a means to generate or measure that tone (i.e. the device on which you are reading this, or perhaps a guitar tuner) then you can simply 'ping' the belt at the middle of the long run between the pulleys and adjust to match the frequency.

This is also a useful technique for finding parts which are likely to vibrate. At 6000rpm, an engine generates a primary frequency of 100 Hz. Anything near that engine which vibrates at 100 Hz or less when you ping it is going to vibrate when the engine is running.

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