VHM Yamaha YZ 125 05-24 Fantic XX 125 21-24 Piston (20mm Pin Bearing)
Details
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VHM Yamaha YZ 125 05-24 Fantic XX 125 21-24 Piston (20mm Pin Bearing)
VHM Yamaha YZ 125 05-24 Fantic XX 125 21-24 Piston (20mm Pin Bearing)
- VHM pistons are 100% CNC machined from high quality material and have a non-circular profile to better prevent engine lockups.
- They stand for high performance, longevity and keeping high performance during it's lifetime.
- This piston consists of an inside coating, which reduces micro welding, lowers the friction on the pin, prevents piston bore galling and provides a very good thermal conduction.
- Furthermore, this piston includes special Z-clips, which prevents the clips from circling and affecting the groove.
- This piston needs a clearance of 0.05mm! Use 20mm wide small end bearing.
| Brand | VHM |
| Modality | Cross/Enduro |
| Primary material | Aluminium |
HOW TO MEASSURE ANY DIRT BIKE´S PISTONS
The pistons of any internal combustion engine, two or four-stroke, are conical and oval, to control its expansion in its operation. To get to know your maximum measurement you have to measure at 10-12 mm. of the skirt, in the opposite part to the bolt.
When we see a mark on the head of the piston, for example, 80 mm. or we have a cylinder of 80 mm. this measure is corresponds to the cylinder, when meassuing the piston we will see that actually measurement is 79.95 mm., the tolerance between piston and cylinder would be 5 cents (0.05 mm.).
In the aluminum cylinders with hard chrome interior treatment, already in disuse, or NIKASIL the measure of 80 mm. It is usually fixed to 80 mm.
The pistons work with tolerances between 4 to 6 hundredths (0.04-0.06) for two-stroke engines and 3 to 4 hundredths for four-stroke engines (0.03-0.04). To fix a deformed cylinder, the interior of the cylinder shall be polished first and the measurement is adjusted with pistons that are over-measured for this purpose, marked with letters A-B-C-D (selection); the lowest measure being A, increasing 1 hundredth per letter; that is, selection B 0.01 mm. greater than A, C 0.02 mm. greater than A, etc.
EXAMPLES
New Cylinder Ø 80.00 mm. mounts a piston of Ø 79,97 A Factory Tolerance 0.03 mm.
Polished Cylinder Ø 80,01 mm. mounts a piston Ø 79,98 B Factory Tolerance 0,03 mm.
Polished Cylinder Ø 80,02 mm. mounts a piston Ø 79,99 C Factory Tolerance 0,03 mm.
Polished Cylinder Ø 80,03 mm. mounts a piston Ø 80,00 D Factory Tolerance 0,03 mm.
The important thing is to maintain the tolerance, which the manufacturer recommends, between cylinder and piston.
