I recently bought a 495 after a long time looking for one. It is a 83 model, in a quite good general condition, with most parts original.
Before start riding the bike, I have now opened the top-end to check piston-cylinder clearance before start riding the bike. The readings taken with the micrometer were:
- Cylinder-top section: 92.77 mm
- Cylinder-central section: 92.87 mm
- Cylinder- bottom –section: 92.74 mm
- Piston (at skirt): 92.63 mm
This gives the following clearance at top/middle/bottom section of the cylinder: 0.14 mm / 0.24 mm / 0.11 mm. This is more than recommendation (0.07 mm).
The piston is a Mahle one, with the number 92.75 mm marked on the head, and is in a quite good condition.
To reduce cylinder-piston clearance we have applied piston coating treatment. Before applying piston coating, the cylinder was honed to a slightly larger diameter in order to recover good geometries, since wear throughout the cylinder was not uniform.
After honing the cylinder and applying piston coating, the final resultant readings were:
- Cylinder-top section: 92.83 mm
- Cylinder-central section: 92.88 mm
- Cylinder- bottom –section: 92.83 mm
- Piston (at skirt): 92.76 mm
This gives the following clearance at top/middle/bottom section of the cylinder: 0.07 mm / 0.12 mm / 0.07 mm, which is now correct.
Cost was 50 € for honing plus 70 € for coating. This is cheaper than honing the cylinder to the next oversize piston and buying a new piston. Finding a new bigger piston could also be a problem sometimes.
Work was done by Picoatec Kolbenbeschichtung in Germany. Excellent quality and service.
www.kolbenbeschichtung.deI have also asked for two new rings, tailor-made to the new cylinder diameter (82.83 mm), since standard rings for the 92.75 mm piston would be small. Spec is 0.15 mm ring end gap when placed at the cylinder.
Next will be to open the crank, since gears to not shift smoothly.
Here some pictures of the cylinder and coated piston.
There are two possible heads: high compression and low compression.
The high compression head:
The low compression head:
Regards,
