G.6 Part. N. 8000 B0148 (02-2008)
ENGINE OVERHAULING
Use a suitable reamer and cutting oil when the valve guide is reamed.
Turn the reamer when it is removed, so that no longitudinal scratches occur.
When a valve guide is replaced, the valve seat must be refaced
Valve
Check that the valve stem and contact surfaces are in good condition. There
should be no pitting, cracks, distortions or signs of wear. Carry out the following
checks:
- Check the valve stem for distortion by resting it on a Vee block and measuring
the distortion with a comparator. (Wear limit: 0.0019 in).
- Check the concetricity of the valve head by resting an angle comparator against
the head and then rotate the valve in a Vee block. (Wear limit: 0.0012 in).
Valve spring
Check the free length “L”. If this does not correspond to the prescribed limits
then substitute the springs.
250cc spring: L= 1.38 in. - Wear limit: 1.3 in.
450-510 cc spring: L= 1.71 in. - Wear limit: 1.6 in.
If it is necessary to change one of the springs then all the other
springs should also be changed.
Check the squareness of the valve springs.
The spring should not deviate by more than 0.059 in. either side.
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