1991 ACURA NSX Service Repair Manual

Piston/Connecting Rod

Assemblies

Inspection

1. Check the piston for distortion or cracks.

NOTE: If cylinder is bored, an oversized piston

must be used.

2. Measure piston diameter at a point 17 mm (0.67 in)

from the bottom of the skirt.

NOTE: There are two standard-size pistons (A =

no letter and B). The letter is stamped on the top of

the piston. These letters are also stamped on the

block as cylinder bore sizes.ProCarManuals.com

Piston/Connecting Ro d
Assemblie s
Inspection
3. Calculat e th e differenc e betwee n cylinde r bor e diam -
ete r o n pag e 7-1 2 an d pisto n diameter .
Piston-to-Bloc k Clearanc e
Standar d (New) : 0.006—0.03 4 m m
(0.0002-0.001 4 in)
Servic e Limit : 0.082 5 m m (0.003 2 in )
0.082 5 m m (0.003 2 in )
Oversiz e Pisto n Diamete r
0.25: 90.226-90.24 4 m m (3.5522-3.553 0 in )
0.50 : 90.476-90.49 4 m m (3.5620-3.562 7 in )
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Connecting Rod s
Selectio n
Each ro d i s sorte d int o on e o f fou r toleranc e range s
(from 0 to 0.02 4 mm , i n 0.00 6 m m increments ) depen -
ding o n th e siz e o f it s bi g en d bore . It' s the n stampe d
with a numbe r (1 , 2 , 3 or 4 ) indicatin g tha t tolerance .
You ma y fin d an y combinatio n o f 1 , 2 , 3 or 4 in an y
engine .
Norma l Bor e Size : 5 3 m m (2.0 9 in )
NOTE :
• Referenc e number s ar e fo r bi g en d bor e siz e an d
d o NO T indicat e th e positio n of the ro d i n th e
engine .
• Inspec t eac h connectin g ro d fo r crack s an d hea t
damage .
CONNECTIN G RO D BOR EREFERENC E NUMBE RHalf o f numbe r i s stampe d o nbearin g cap , th e othe r hal f o nconnectin g rad .
Inspec t bolt sand nut s fo rstres s cracks .
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Piston Ring s
End Ga p
1. Usin g a piston , pus h a ne w rin g int o th e cylinde r
bor e 1 5 - 2 0 m m (0. 6 - 0. 8 in ) fro m th e bottom .
2 . Measur e th e pisto n rin g end-ga p wit h a feele r
gauge :
• I f th e ga p i s to o small , chec k t o se e i f yo u hav e
the prope r ring s fo r you r engine .
• I f th e ga p i s to o large , rechec k th e cylinde r bor e
diameter against th e wea r limit s o n pag e 7-12 . I f
th e bor e i s ove r limit , th e cylinde r bloc k mus t b e
rebored .
Pisto n Rin g End-Gap :
To p Rin g
Standar d (New) :
0.25-0.4 0 mm
(0.010-0.01 6 in )
Servic e Limit : 0.6 0 m m (0.02 4 in )
Secon d Rin g
Standar d (New) :
0.35-0.5 0 mm
(0.014-0.02 0 in)
Servic e Limi t 0.7 5 m m (0.0 3 in )
Oi l Rin g
Standar d (New) :
0.20-0.7 0 mm (0.008-0.02 8
in)
Servic e Limit : 0.8 0 m m (0.03 1 in )
Replacemen t
1. Usin g a rin g expander , remov e th e ol d pisto n rings .
2 . Clea n al l rin g groove s thoroughly .
NOTE:
• Us e a squared-of f broke n rin g o r rin g groov e
cleane r wit h blad e t o fi t pisto n grooves .
• To p an d 2n d rin g groove s ar e 1. 2 m m (0.0 5 in )
wid e an d th e oi l rin g groov e is 2. 8 m m (0.1 1 in )
wide .
• Fil e dow n th e blad e i f necessary .
CAUTION : D o no t us e a wir e brus h to clea n th e rin g
grooves , o r cu t rin g groove s deepe r wit h a cleanin g
tool .
3 . Instal l ne w ring s i n th e prope r sequenc e an d posi -
tio n (se e pag e 7-16 ).
NOTE : D o no t reus e ol d pisto n rings .
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Piston Ring s
Ring-to-Groov e Clearance s
After installin g a ne w se t o f rings , measur e ring-to-groov e
clearances:
Top an d Secon d Rin g Clearanc e
Standar d (New) :
0.030-0.05 5 mm
(0.00 1 - 0.00 2 in )
Servic e Limit : 0.1 3 m m (0.00 5 in )
FEELE R GAUG E
Alignmen t
1. Instal l th e ring s a s show n o n pag e 7- 15.
Identif y to p an d secon d ring s b y th e chamfe r o n th e
edge , an d mak e sur e the y ar e i n th e prope r groove s
i n th e piston .
NOTE : Th e manufacturin g mark s mus t b e facin g
upward .
2. Rotat e th e ring s i n thei r groove s t o mak e sur e the y
do no t bind .
MAR K
TO P RIN G
SECON D RIN G
OI L RIN G MAR
K
- SPACE R
3. Positio n th e rin g en d gap s a s shown :
SECON D RIN G CA PDO NO T positio n an y rin g ga pat pisto n thrus t surfaces .
TOP RIN G GA P
DO NO T positio n an y rin g ga pin lin e wit h pisto n pi n hole .OIL RIN G GA P
SPACE
R GA P
OI
L RIN G
GAP
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Piston/Connecting Ro d Assemblie s
Installation
Before installin g th e piston , appl y a coa t o f
engin e oi l t o th e rin g groove s an d cylinde r
bores.
1. I f th e crankshaf t i s alread y installed :
• Guid e th e pisto n carefull y t o preven t damage .
• Fi t lon g rubbe r hose s (abou t 3 0 c m (1 2 in ) long ) t o
th e connectin g ro d bolt s t o protec t th e crankshaft .
• Instal l th e piston s afte r settin g th e crankshaf t t o
BD C fo r eac h cylinder .
CORREC TINCORREC T
RUBBER HOSE S
Install th e pisto n assemblie s i n No . 1 an d No . 4
cylinders , No . 2 an d No . 5 cylinders , an d No . 3
an d No . 6 cylinders .
Instal l th e rin g compressor , chec k tha t th e bear -
in g i s securel y i n place ; the n positio n th e pisto n
i n th e cylinde r an d ta p i t i n usin g th e woode n
handl e of a hammer .
Sto p afte r th e rin g compresso r pop s fre e an d
chec k th e connectin g rod-to-cran k journa l align -
ment befor e puttin g ro d int o place .
Install th e ro d cap s wit h bearings , an d torqu e th e
nut s t o 2 0 N- m (2. 0 kg-m , 1 4 Ib-ft) , the n tur n th e
nu t 9 5 degree s (se e pag e 7-19 ).
If th e crankshaf t i s no t installed :
• Remov e th e ro d cap s an d bearings , instal l th e
ring compressor , the n positio n th e pisto n in th e
cylinde r an d ta p it i n usin g th e woode n handl e of
a hammer .
The arro w mus t fac ethe timin g bel t sid eof th e engin e an d th econnectin g ro d oi l hol emus t fac e th e rea r sid eof th e engine .
CONNECTIN G RO DOIL HOL E
NOTE : Maintai n downwar d forc e o n th e rin g com -
presso r t o preven t ring s fro m expandin g befor e
enterin g th e cylinde r bore .
Use th e woode n handl eof a hamme r t o push , o rtap th e pisto n int o th ecylinde r bore .
RING COMPRESSO R
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Crankshaft

Installation

Before installing the crankshaft, apply a coat of

engine oil to the main bearings and rod

bearings.

1. Insert bearing halves in the engine block and con-

necting rods.

2. Lower the crankshaft into the block.

3. Install the thrust washers on the No. 3 journal. Oil

thrust washer surfaces.

4. Install the bearings and caps. Tighten 9 x 1.25 mm

cap bolts to the specified torque.ProCarManuals.com

NOTE:
• Guid e th e pisto n carefull y t o preven t damage .
• Fi t lon g rubbe r hose s (abou t 3 0 c m long ) t o con -
nectin g ro d bolt s t o protec t th e crankshaft .
• Instal l th e piston s afte r settin g th e crankshaf t t o
BD C fo r eac h cylinder .
CORREC TINCORREC T
RUBBER HOSE S
9 x 0.7 5 mm20 N- m (2. 0 kg-m , 1 4 Ib-ft )
afte r tur n t o 95 °
MAR K
• Lin e u p th e mark s whe n installin g connectin g
rod cap .
5. Chec k th e ro d bearin g clearanc e wit h plastigag e
(se e pag e 7-7 ), the n torqu e th e connectin g ro d ca p
nuts .
NOTE : Referenc e number s o n connectin g rod s ar e
fo r big-en d bor e toleranc e an d d o NO T indicat e th e
positio n o f pisto n i n engine .
CONNECTIN G RO D CA P NU T TORQUIN G
METHOD
1) Torqu e th e connectin g ro d ca p nu t t o 2 0 N- m
(2. 0 kg-m , 1 4 Ib-ft ) wit h a beam-typ e torqu e
wrench .
2 ) Instal l a torqu e angl e gaug e t o th e ca p nut , the n
tur n th e ca p nu t 9 5 degrees .
Snap-onTA360 o requivalen t
BEARIN
G CA P
WASHERS
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