Faq Technical Area - Engine

Found 12

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How can I find the displacement of a power kit?
The displacement can be calculated through the following formula: Displacement= (DxDx3,1416xC)/4=DxDxCx0,7854 D= Bore (the piston's diameter) C= Stroke (distance between top and bottom dead centre)
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How much tolerance must the piston have with the aluminium cylinder?
The foreseen tolerance must be included between 3 and 3 cents (0,03 - 0,06)
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How much tolerance must the piston have with the cats-iron cylinder?
The foreseen tolerance must be included between 6 and 8 cents (0,06 - 0,08)
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I have just fitted a new 4 stroke cylinder and it makes a lot of smoke. What may I do?
Probably when assembling the piston, the spring located under the 2 scraper rings has broken. Change all the rings.
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I'm fitting my new piston. What's the direction of the arrow I find on the top of the piston?
The arrow must be directed towards the exhaust port.
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If I fit one of your "freer" air filters, do I to change the jets?
Yes, you have. Usually it is enough to increase the main jet. We suggest immediately increasing of 10 points and then adjust it according to the carburetion.
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What kind of oil may I use for the mixture? In what percentage?
Use 2% synthetic oil
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What spark plug have I to fit on my power unit?
Please, check the assembling instructions of the kit you have fitted.
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What's the difference between piston A, B, C or D?
The piston with letter A has the smallest diameter, while the one with letter D is the biggest one. Every different letter means an increase of 0,01 mm.
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When have I to change my piston?
It depends on the cylinder kit you have fitted and on what kind of races you take part in. Generally a standard cast iron cylinder the piston lasts 5000/8000 km. The cast iron racing type can last 3000/5000 km, the evolution aluminium ones 500/1000 km. If your engine has been tuned up to take part to the Polini Italian Cup you have to change the piston every two races.
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When Have I to change the ring?
The wear of the ring should be the same as the piston. We do not recommend changing the ring only.
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Why is Polini ignition better than the standard unit? What are the advantages?
The most important advantage of the Polini ignition is the rotor. The flywheel inertial mass has been drastically reduced and you immediately find a better pick up. The advance curve has been studied for every kind of use of the engine and it has been personalised according to the brand and model.

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