261
Chapter 13 Preventive Maintenance and Troubleshooting
Figure 13-33.
Identifi cation numbers found on an engine provide
valuable information. This sticker displays the engine’s
build date and serial number.
Tolerances and Clearances for the J-321 Engine
Cylinder bore Max.
Min.
2.1265″
2.1260″
Piston skirt diameter Max.
Min.
2.1227″
2.1220″
Piston ring width Max.
Min.
.0935″
.0925″
Piston pin diameter Max.
Min.
.5001″
.4999″
Spark plug gap .030″
Piston skirt to cylinder
clearance
Max.
Min.
.0045″
.0033″
Figure 13-32.
Typical tolerance and clearance chart. (Jacobsen Mfg. Co.)
Engine Troubleshooting Chart
Cause Remedy
Engine uses excessive amount of oil (four cycle only)
Engine speed too fast. Using tachometer, adjust engine RPM to specifi cations.
Oil level too high. To check level, turn dipstick cap tightly into receptacle
for accurate level reading. Drain excess oil as needed.
Oil fi ller cap loose or gasket damaged causing spillage
out of breather.
Replace ring gasket under cap and tighten cap securely.
Breather mechanism damaged or dirty causing leakage. Replace breather assembly.
Drain hole in breather box clogged causing oil to spill
out of breather.
Clean hole with wire to allow oil to return to crankcase.
Gaskets damaged or gasket surfaces nicked, causing
oil to leak out.
Clean and smooth gasket surfaces. Always use new
gaskets.
Valve guides worn excessively thus passing oil into
combustion chamber.
Ream valve guide oversize and install 1/32″ oversize
valve.
Cylinder wall worn or glazed, allowing oil to bypass
rings into combustion chamber. Piston rings and
grooves worn excessively.
Bore, hone, or deglaze cylinder as necessary.
Reinstall new rings, check land clearance, and correct
as necessary.
Piston fi t undersized. Measure and replace piston as necessary.
Piston oil control ring return holes clogged. Remove oil control ring and clean return holes.
Oil passages obstructed. Clean out all oil passages.
Figure 13-31.