Onan MJA Series Service Manual page 82

3.8 Pistons, Connectinq Rods & Cylinders
MJ generati.."'1g sets use tapered aluminum pistons which are fitted with
2 compression rings and an oil control ring. Full floating piston pins
connect the piston to its connecting rod. The pins are held in place with
a snap ring at each end. The lower end of each connecting rod contains
balf shell, precision bearings and the upper end, a semi-finished bush­
,ing.
NOTE: Some generating plants are fitted with. 005" oversize pistons
at the factory. These plants are marked with an E following the
plant serial number. Use standard size rings for these pistons.
I)
3.8.1 REMOVAL AND DISASSRMBLY
(
On 2 and 4 cylinder engines, the connecting rod and cap are stamped
for installation
i:1
the proper cylinder. When removing piston assem­
blies, check the marking so each can be reinstalled in the proper cyl­
inder and keep aU components of each piston assembly together.
1. Drain the crankcase oil and remove the oil base.
2. Drain the water jacket and remove the cylinder heads.
3. Clean carbon deposit from top of each cylinder.
4. Remove the cap from each connecting rod and push the assembly
through the top of the cylinder bore. Replace the cap aI)d bearing
inserts in the proper assembly.
5. U sing
a
ring expander,
HEAVIEST COMPRESSION
RING IN TOP GROOVE
COMPRESSION RINGS
OIL CONTROL RING
£>:PJlNDER
*RAILS ARE NOT U<;ED ON
TVIC CYLINDER ENGINES,
_rerpove the ?lngs
~rom
each piston.
I.
i
@
i
. FEELER
GAUGE
FIG 3.8. A - PISTON RINGS, LOCATION & GAP