Generac Power Systems GTV99O Service Manual page 55

SECTION 12: PISTON, RINGS & CONNECTTNG
ROD tNSpECTtON & ASsEMBLy
SEcTION CONTENTS
PAGE
G E N E R A L
T N F O R M A T / O N . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 2 _ l
D I S A S s E M B L E
P I S T O N A N D C O N N E C T I N G
R O D . . . . , . . . . . 1 2 , ]
c H E C K T N G
p t S T O N A N D R ] N G S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . .
1 2 , 1
CHECKING PISTON PIN AND CONNECTING
ROD
.... 12 2
A S S E M E L E
p t S T O N A N D C O N N E C T T N G
R O D . . . . . . . . . . . . . . . .
1 2 2
AsSEMBLE PJSTON RTNGS TO ptSTON ................. .
12,3
GENERAT INFORMATION
It is recommended that new piston rings be innalted when-
ever the engine is disassembled
for rnajorservicing
or overnaur,
provdr,rg thar ryhnde bo.es are wtl ir sperrfrcation.
Remove any carbon or ridge atthe top of the cylinder bore.
This will prevent breaking the ringswhen removingthe piston
and connecting rod from the engine. Remove the connedring
rod cap. Push the piston and connecting rod out through the
top of the cylinder
Measure cylinder bores before checking pistons and ringr.
see Sedion 10.lf cylinder bor€s are outoftolerance, it willnot
be necessarytoaheck pistonsand rrngssince a newcrankcase
and piston assemblies willbe used.
ll the cylinder bore is more than .075 mm {.003,) oversize,
or .035 mm (.0015") out of round, it must be replaced.
DISASSEMBLE PISTON AND CONNECTING ROD
1. Remove piston rings using ring expander.
a. fhen remove oil ring.
Figurc t2-t. Renove Rjngs
2. Disassemble piston from connecting rod, Figure t2-2.
a Remove piston pin locks.
b. Piston pin is a slip fit in prston and connecting rod.
Keep pGtons and connecting rods together as an assembly
Do not mix,
Figurc 12-2, Remove pistoD pin Lock
CHECKING PISTON AND RINGS
lf the cylinderis not goingto be replaced andthe prnon snows
no signs of scoring, the piston should be checked. Carefully
remove ca|bon from ring grooves.
1. Checkside clearance of ring grcoves using new rjngs, Figure
I 2-3.' a 0.1omm ( 004"\ feeter gduge fo. t're ( ompres\ion
ngs or 0.20mm (.008") for the ojlring can be tnseneo, tne
flng groove |5 worn. The piston must be replaced.
Figurc 12-3. Check Ring crcoves
2. Check ring end gap, Figure 12-4.
a. Clean c.|bon from end of rings and insert approximatety
1 {25 firm) into cyllnder
Reiect Dimension (comqession ngs):.020" (O.S1mm)
Reiect Dimension (oil rings): .045" (1 .1 Snm)
b.lf gap is less than rejec dimension, remove some maer
i a l ' r o m $ F e n d o . r n e i n g t o a c h e v e r 1 e m i n i ^ J m g a p
3. Check piston pln bore, Figuret2 5.
a. Reptace if grearer than .7886' (20.03mm) or jf ir is .OOO5 ,,
(01 mm) out of round.
t