Generac Power Systems 53187 - Manual (Page 74)

PART 2
ENGINE MECHANICAL SECTION 2.4
DISASSEMBLY AND INSPECTION
Figure 16. Piston Pin Rem oval
PISTON INSPECTION:
Inspect the piston, replace if dam aged, cracked,
scored, burned, etc. Check the diam eter of the piston
skirt, about 0.394 incvh (10m m ) from bottom . Also
check the inside diam eter of the cylinder. Then, calcu­
late the piston to cylinder clearance. If the clearance
exceeds the allow able lim it or if the piston diam eter is
less than the allow able lim it, replace the piston. W hen
a cylinder is oversized, use a correspondingly oversize
piston. The follow ing apply:
□ Standard piston to cylinder clearance Is 0.003-
0.005 Inch (0.070-0.119mm). Allowable limit is
0.010 Inch (0.25mm).
□ Standard largest diameter of the piston skirt Is
2.9488-2.9500 inch (74.900-74.930mm). Allow­
able limit is 2.9409 inch (74.7mm).
Pistons and Piston Rings (Continued)
Check the diam eter of the piston pin hole and the
outside diam eter of the piston pin. Calculate the clear­
ance betw een the piston pin and piston pin hole. If
clearance is greater than the allow able lim it, replace the
piston.
□ standard piston pin hole to pin clearance is
minus 0.00008-plus 0.0003 Inch (-0.002-
••■ 0.008mm).
□ Allowable hole to pin clearance limit is 0.0008
Inch (0.02mm).
PISTON RINGS:
Inspect rings, replace if w orn or dam aged. Install
the rings into the cylinder skirt and check ring gaps w ith
a feeler gauge. Replace rings if allow able lim its are
exceeded.
□ standard gap of No. 1 Ring = 0.008-0.014 inch
(0.2-0.35mm)
□ standard Gap of No. 2 Rlng=0.006-0.012 inch
(0.15-0.3mm)
□ Standard Gap of Oil Ring=0.008-0.01 Inch (0.2-
0.35mm)
□ Allowable Limit (All Rings) = 0.039 inch (1.0mm)
PISTON PART NO. PISTON SKIRT DIAMETER*
Standard
0.5mm O.S
1.0mm O.S
214- 7093&
215-
70939
216- 70939
2.9488-2.9500 inches
2.9685-2.9697 inches
2.9682-2.9894 inches
' Largest diameter of piston skirt is given.
PISTON RING GROOVE TO RING CLEARANCE:
Measure the clearance betw een the piston ring
groove and the ring. If allow able lim its are exceeded^
replace the ring.
□ No. 1 Ring Standard Clearance s 0.002-0.004 inch
(0.06-0.1 mm)
□ No. 2 Ring Standard Clearance = 0.002-0.0035
Inch (0.05-0.09mm)
□ No. 1 and 2 Ring Allowable Limit = 0.010 inch
(0.25mm)OII Ring Standard Clearance = 0.0008-
0.006 inch (0.02-0.06mm)
□ Oil Ring Allowable Limit = 0.006 inch (0.15mm)
Figure 17. Checking Piston Fit
PAGE 2.4-5