Piston Check - Rotax 912 Series Maintenance Manual

AIRCRAFT ENGINES
MAINTENANCE MANUAL II
14.6.1)

Piston check

See fig. 175 and 176.
The engine type 912 Series has cast light alloy, full skirt pistons. The piston
axis is offset by 1 mm (.039 in.).
Remove piston rings using a pair of piston ring pliers.
CAUTION: Make absolutely sure to re-fit rings in their initial position.
Check piston rings and ring grooves for oil carbon residues. The best way
to clean piston ring grooves is by using a piece of a broken ring. Increased
amount of residue is to be expected when using AVGAS 100LL. Remove
carbon deposits from piston crown.
Visually check and measure piston. Piston and/or cylinder must be
renewed if piston to wall clearance exceeds 0,1 mm (.004 in.). To
determine this clearance, measure cylinder bore by internal caliper with
dial gauge, to find the biggest piston dia. (most probably found at the
position Q depicted), see dimension D in para 15.
Comparing the 2 dimensions — smallest cylinder dia. less biggest piston
skirt dia. — is the piston to cylinder clearance.
Visually inspect groove for piston pin circlip W. At presence of a burr
remove it carefully. If the groove is excessively worn (> 0,3 mm = .012 in.),
renew piston.
2 dimension groups of pistons are available, marked by a red or green
colour dot on piston crown. Nominal dimension differs by 0,01 mm. The
piston with red dot is the smaller one. The nominal dimension is stamped
on the piston crown. There are no oversize pistons planned. The piston is
supplied only complete with 3 rings.
1
Nullhakenring /
circlip
75
2
2
D
fig. 175
fig. 176
75—100 mm
04708
1/100 mm
04707
Effectivity: 912 Series page 110
Initial issue, Jan. 01/2002