NB: These instructions are given for guidance only and cannot engage the author's or JLO-Tech's liability in the event of misinterpretation, failure to assess the vehicle's actual condition and/or non-conformity, unsuitable mechanical practice or the use of inappropriate tools. Piston installation, cylinder reboring and preliminary checks (lubrication, ignition/carburation tuning) are entirely the mechanic's responsibility.
Ross Racing pistons and rings (translation of the original notice, adapted to Laverda engines). Forged pistons (2618 T-61 aluminium), forced lubrication with oil-transfer grooves, balanced to ± 2.5 g, valve pockets for big valves and high-lift cams.
Kit contents
- Piston, gudgeon pin, 2 circlips.
- A pack of rings: oil control (oil groove), compression/scraper (2nd groove) and top/fire (top groove).
Fitting the rings
- Oil control (first): coil the expander spring with the end tips touching and pointing down. Then fit the two rails, upper before lower (otherwise fitting is awkward). Set the upper rail gap ~90° anticlockwise from the expander gap, the lower rail gap ~90° clockwise: this avoids excessive mechanical stress and the expander ends overlapping.
- 2nd groove ring: dot/mark facing up.
- Top ring: dot up; failing that, internal chamfer up; with neither dot nor chamfer the ring is symmetrical (either way).
Space the top and 2nd-groove ring gaps ~180° apart. Lubricate pistons and rings with a quality 20W50 minimum oil (avoid low-viscosity monogrades; avoid additives until the bores are run in).
Clearances (Laverda engine)
- Piston-to-bore clearance: optimal 0.075 mm.
- End gaps (the Ross top and 2nd rings are oversize and must be filed to fit): top 0.35 mm, 2nd 0.40 mm. Leave the oil-control rails as supplied.
- Ring side clearance in groove (on later replacement): 0.05-0.10 mm (top and 2nd), 0.08-0.12 mm (oil control).
- Ring recess in groove (rings pushed fully in): ~0.10 mm (top and 2nd), ~0.80 mm (oil control).
Cylinder honing
When reboring, leave a 0.08 mm margin for honing. Two passes recommended: 1st pass ~0.01 mm under final bore (220-grit stone), final pass (400 stone). Hone speed ~300 rpm, 30° cross-hatch. Work carefully so as not to burn the bore wall.