Snowmobile Yamaha FX10X, FX10RTX, FX10RTRX, FX10RTRAX, FX10MTX, FX10MTRX, FX10MTRAX. Manual - part 60

5-60

ENG

CONNECTING RODS AND PISTONS

2nd step:

• Measure piston skirt diameter “P” with the

micrometer.

a 11.0 mm (0.43 in) from the bottom edge of the piston.

• If out of specification, replace the piston and

piston rings as a set.

3rd step:

• Calculate the piston-to-cylinder clearance with

the following formula.

Piston-to-cylinder clearance = 

Cylinder bore “C” –
Piston skirt diameter “P”

• If out of specification, replace the crankcase,

and the piston and piston rings as a set.

Piston size (standard) (P):

81.950 ~ 81.965 mm
(3.2264 ~ 3.2270 in)

Piston-to-cylinder clearance:

0.035 ~ 0.060 mm
(0.0014 ~ 0.0024 in)
<Limit>: 0.120 mm (0.0047 in)

3. Measure:

• Piston ring side clearance

Use the thickness gauge 1.
Out of specification 

→ Replace the piston and

piston rings as a set.

NOTE:

Eliminate the carbon deposits from the piston ring
grooves and rings before measuring the side clear-
ance.

Piston rings side clearance:

Top ring:

0.030 ~ 0.070 mm
(0.0012 ~ 0.0028 in)

2nd ring:

0.020 ~ 0.060 mm
(0.0008 ~ 0.0024 in)

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CONNECTING RODS AND PISTONS

4. Install:

• Piston ring

(into the cylinder)

NOTE:

Level the piston ring in the cylinder with the piston
crown.

a 5.0 mm (0.20 in)

5. Measure:

• Piston ring end gap

Out of specification 

→ Replace the piston

rings as a set.

NOTE:

The oil ring expander spacer end gap cannot be
measured. If the oil ring rail gap is excessive,
replace all three piston rings.

6. Inspect:

• Piston pin

Blue discoloration/grooves 

→ Replace the

piston pin and then check the lubrication sys-
tem.

Piston ring end gap:

Top ring:

0.33 ~ 0.45 mm (0.013 ~ 0.018 in)

2nd ring:

0.70 ~ 0.85 mm (0.028 ~ 0.033 in)

Oil ring:

0.20 ~ 0.60 mm (0.008 ~ 0.024 in)

7. Measure:

• Piston pin outside diameter

Out of specification 

→ Replace the piston pin.

Piston pin outside diameter:

18.991 ~ 19.000 mm
(0.7477 ~ 0.7480 in)

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CONNECTING RODS AND PISTONS

8. Measure:

• Piston pin bore inside diameter

Out of specification 

→ Replace the piston.

Piston pin bore inside diameter:

19.004 ~ 19.015 mm
(0.7482 ~ 0.7486 in)

9. Calculate:

• Piston pin to piston pin bore clearance

Out of specification 

→ Replace the piston pin

and piston as a set.

Piston pin to piston pin bore clearance = 

Piston pin bore size –
Piston pin outside diameter

Piston pin to piston pin bore clear-
ance:

0.004 ~ 0.024 mm
(0.0002 ~ 0.0009 in)
<Limit>: 0.074 mm (0.0029 in)

10. Measure:

• Crankshaft-pin-to-big-end-bearing clearance

Out of specification 

→ Replace the big end

bearings.

Crankshaft-pin-to-big-end-bearing 
clearance:

0.033 ~ 0.050 mm
(0.0013 ~ 0.0020 in)

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CONNECTING RODS AND PISTONS

Measurement steps:

CAUTION:

Do not interchange the big end bearings and
connecting rods. To obtain the correct crank-
shaft-pin-to-big-end-bearing clearance and pre-
vent engine damage, the big end bearings must
be installed in their original positions.

• Clean the big end bearings, crankshaft pins,

and bearing portions of the connecting rods.

• Install the big end upper bearing into the con-

necting rod and the big end lower bearing into
the connecting rod cap.

NOTE:

Align the projections 

a on the big end bearings

with the notches 

b in the connecting rod and con-

necting rod cap.

• Put a piece of Plastigauge

®

  1 on the crank-

shaft pin.

• Assemble the connecting rod halves.

NOTE:

• Do not move the connecting rod or crankshaft

until the clearance measurement has been com-
pleted.

• Apply molybdenum disulfide grease onto the

bolts, threads, and nut seats.

• Make sure that the “Y” mark 

c on the connecting

rod faces towards the right side (AC magneto
rotor side) of the crankshaft.

• Make sure that the characters 

d on both the con-

necting rod and connecting rod cap are aligned.

1

6E

Y

d

c