Chapter 1 Engine, clutch and gearbox
31
A certain amount of side play is intentional, and should be
between
-
mm
-
in) on a new crank-
shaft. The maximum allowable side play is
mm ( 0 0 3 2 in)
and can be checked with a feeler gauge between the flywheel
face and the edge of the connecting rod.
2 It is not possible to separate the flywheel assembly in order
to replace the bearing because the parallel sided crankpin is
pressed into the flywheels. Big-end repair should be entrusted
to a Honda agent, who will have the necessary repair or
replacement facilities.
3 Failure of the main bearings is usually evident in the form of
an audible rumble from the bottom end of the engine,
accompanied by vibration. The vibration will be most noticeable
through the footrests.
4 The crankshaft main bearings are of the journal ball type. If
wear is evident in the form of play or if the bearings feel rough
as they are rotated, replacement is necessary. To remove the
main bearings if the appropriate service tool is not available,
insert two thin steel wedges, one on each side of the bearing,
and with these clamped in a vice hit the end of the crankshaft
squarely with a rawhide mallet in an attempt to drive the crank-
shaft through the bearing. When the bearing has moved the
initial amount, it should be possible to insert a conventional two
or three legged sprocket puller, to complete the drawing-off
action.
18.1a Use steel wedges and a puller to remove worn main
bearings
/i
Mark pinion relative to shaft before withdrawing pinion
Bearings can be tapped out of the cases using large drift
20 Examination and renovation: gudgeon pin, small end and
piston bosses
1 The fit of the gudgeon pin in both the small end eye of the
connecting rod, and in the piston bosses should be checked. In
the case of the small end eye, slide the pin into position and
check for wear by moving the pin up and down. The pin should
be a light sliding fit with no discernible radial play. If play is
detected, it will almost certainly be the small end eye which has
worn rather than the gudgeon pin, although in extreme cases,
the latter may also have become worn. The connecting rod is
not fitted with a bush type of small end bearing, and conse-
quently a new connecting rod will have to be fitted if worn. This
is not a simple job, as the flywheels must be parted to fit the
new component, and is a job for a Honda Service Agent. It
should be borne in mind that if the small end has worn, it is
likely that the big-end bearing will require attention.
2 Check the fit of the gudgeon pin in the piston. This is nor-
mally a fairly tight fit, and it is not unusual
the piston to have
to be warmed slightly to allow the pin to be inserted and
removed. After considerable mileages have been covered, it is
possible that the bosses will have become enlarged. If this
proves to be the case, it will be necessary to renew the piston to
effect a cure. It is worth noting, as an aid to diagnosis, that wear
in the above areas is characterised by a metallic rattle when the
engine is running.
21 Examination and
piston and piston rings
1 If a rebore is necessary, the existing piston and rings can be
disregarded because they will be replaced with their oversize
equivalents as a matter of course.
2 Remove all traces of carbon from the piston crown, using a
soft scraper to ensure the surface is not marked. Finish off by
polishing the crown, with metal polish, so that carbon does not
adhere so easily in the future. Never use emery cloth.
3 Piston wear usually occurs at the skirt or lower end of the
piston and takes the form of vertical streaks or score marks on
the thrust side. There may also be some variation in the
thickness of the skirt. Measure the piston skirt outside diameter
at right angles to the gudgeon pin axis and at a point 10 mm
(0.4 in) above the base of the skirt; renew the piston if it is
found to be scored, damaged or worn to the specified wear limit
or beyond.
4 The piston ring grooves may also become enlarged in use,
allowing the piston rings to have greater side float. If the
clearance exceeds
mm ( 0 0 0 4 in) for the two compression
rings, the piston is due for renewal. It is unusual for this amount
of wear to occur on its own.
