Operation Manual

- Inspect the coupling surfaces on the crankcase
halves for scratches or deformation, taking partic-
ular care with the cylinder/crankcase surfaces and
the crankcase halves surfaces.
- Defects in the crankcase coupling gasket be-
tween the crankcase halves or the mating surfaces
shown in the diagram, could cause a drop in the
oil pressure lubricating the main bearings and con-
nection rod.
- Check the main bearing seats that limit axial
clearance in the crankshaft show no signs of wear.
The dimension between these seats is measured
by way of the procedure described previously for
measuring the crankshaft axial clearance and di-
mensions.
N.B.
THE JET IS FED THROUGH THE MAIN BUSH-
INGS. PROPER OPERATION OF THIS COMPO-
NENT IMPROVES THE PISTON TOP COOLING.
CLOGGING HAS EFFECTS THAT ARE DIFFI-
CULT TO DETECT (PISTON TEMPERATURE
INCREASE). FAILURE OR LEAK CAN CONSID-
ERABLY DECREASE THE MAIN BUSHING
AND CONNECTING ROD LUBRICATION PRES-
SURE.
N.B.
THE HEAD LUBRICATION CHANNEL IS PRO-
VIDED WITH A SHUTTER JET; THIS GIVES A
"LOW PRESSURE" HEAD LUBRICATION; THIS
CHOICE WAS MADE TO REDUCE THE OIL
TEMPERATURE IN THE SUMP. THE JET
CLOGGING IMPAIRS THE HEAD LUBRICA-
TION AND THE TIMING MECHANISMS. A JET
FAILURE CAUSES A DECREASE OF THE MAIN
BUSHING AND CONNECTING ROD LUBRICA-
TION PRESSURE.
MP3 250 i.e. Engine
ENG - 53