|1. Picture shows the Indian-Four
clutch body. Against the projecting hub, rear side of engine, a sprocket
is mounted which drives the transmission. This hub (arrow) was trued up
by grinding and is supported in the crankcase, by originally a babbitt
lined bronze shell or nowadays a sometimes used solid aluminium/tin "clutch
bearing". At the other side (engine front side) of this clutch body there
is a pressed in bronze bush. The body rotates on the crankshaft "nose",
when the clutch is disengaged. Although made precise by the factory including
the 2 inspection holes, the outer rim can be a little eccentric, so it
is advisable to balance the clutch body dynamically (arrow).
|2. Picture shows the bronze bush. On an
extension of the bush one part of a pressure ball bearing is fitted (arrow).
In this case the indentations on the outer rim (arrow) are trued up, so
when disengaging, the inner clutch plates can separate more easily. The
weight of the body including the steel inner clutch plates is considerable,
which results in pressure on the oil film. This film has to prevent metal
to metal contact when the the bronze bush rotates on the crankshaft.
|3. Originally the factory made an axial
oil groove which stops 6 mm / 0.25" before the front side end of the bush
(arrow), so there will be no loss of oil pressure as the oil flows in by
pressure from the rear side (transmission side). The oil groove has a 6
degree inclination towards the front side end of the bush. The bronze bush
can show wear, already after a few thousand miles. Besides inducing vibration,
this also can cause some loss of oil pressure. An axial oil groove breaks
the oil film more easily which causes metal to metal contact . The picture
shows the wear.
|4. Picture shows a bronze bush in an Ace
clutch body (this body has a smaller outside diameter than the Indian-Four
body). Three axial oil grooves can be seen extending till the front side
end of the bush. If there is no pressure lubrication, the system can work,
especially when the speed of rotation is limited. (When measuring the inside
diameter this bush is a little oval, so there is some wear but otherwise
very smooth inside. The correct type of bronze was used, 8% tin.)
|5. All the Four crankshafts have an oil
hole at the end of the crankshaft "nose" (arrow in picture 9). The later
Fours have an additional oil hole about halfway the hub length of the "nose".
In early Fours it will be an improvement to make this hole with a bevel
around it to ease the oil flow. Diameter: 3 mm / 0.125" (see picture 8,
arrow). When there is such an oil hole one could make instead of the axial
groove, a circular oil groove (width: 4mm/0.15"), positioned exactly at
the oil hole. The edges of the groove are eased off. The oil flow now comes
from two sides into the bush: from the rear and from the additional made
hole. Together with the circular groove, the oil film will be maintained
under pressure and there will be no loss of oil pressure.
|6. The clearance of the "clutch (body)
bearing" is measured (0.04 mm / 0.001574"). Check if the body spins well.
If not, before torquing down the bearing cap completely, give some blows
with a hammer on the cap to center it. Check again. Mark in which direction
the blows were given as in a later stage, when the clutch is completely
assembled it is not possible to test the body separately. Watch the aluminium/tin
bearings used here (min. 18% tin). Because this material is harder than
babbitt and can not incorporate dirt, the crankshaft has to be surface
hardened (or hard chromed etc.) to prevent scoring of the hubs. Usually
the hardness of a plain bearing is 20% or less than the hardness of a hub.
On the # 4 crankshaft bearing from aluminium/tin it can be seen that the
shell stands a little proud (arrow) of the ground bearing flange. After
torquing down the bearing cap, the shells will be "pulled up".
|7. Bronze bush and crankshaft "nose" clearance:
0.02 - 0.025mm (0.001"). All bearing caps are torqued down with the same
torque as during the align-boring procedure. The clutch body and crankshaft
are rotated by hand in a direction opposite to each other. If at a certain
point resistance is felt, the crankshaft "nose" has to be checked. (The
red paint mark -arrow- on the crankshaft flange is related to the position
of the fly wheel during the dynamic balancing procedure.)
|8. The correct sequence would be checking
the crankshaft "nose" with a clock before turning the bronze bush. The
bush has to be of the correct bronze composition. Preferably honed to size
and with a very light press fit and Locktite pressed into the ground hole
of the clutch body. It seems sometimes difficult for a machinist
to ground the "nose" in line with the main bearing hubs, because after
grinding these, he has to use a steady-support to do the job. The arrow
the crankshaft shows the crankshaft was
ground during the balancing process.
|9. If the eccentricity is not more than
0.03 mm/0.0015" this can be corrected with fine emery cloth till no resistance
is felt when rotating (step 7). If the eccentricity is more, the "nose"
has to be brought in line with the main bearing hubs and reground. After
definite assembly the nuts are secured by wire so the studs too will not
become loose as the prescribed torque is not that high.