Cylinders - Tecumseh ECV105 Technician's Handbook

CYLINDERS

Visually check the cylinder for broken or cracked fins or a scored cylinder bore. Check the main bearings for wear or
scoring. If the main bearings are worn or scored they can be replaced on some models. See "Crankshaft Bearing
Service" in this chapter.
Use a dial bore gauge or telescoping gauge with a micrometer to accurately measure the cylinder bore. Measure in
the piston travel area approximately 1/2 to 3/4 of an inch (12.7 to 19.05 mm) from the top and the bottom . Measure at
90 degrees to the piston pin, 45 degrees to the piston pin, and even with the piston pin as the piston would appear
when assembled. A rigid hone is recommended to "true" any cylinder irregularities. If the cylinder bore is worn more
than .005" (.127 mm) oversize, out of round or scored, it should be replaced or re-sized to .010 or .020 oversize (.254
mm or .508 mm). In some cases engines are built with oversize cylinders. If the cylinder is oversize, the oversize value
will be imprinted in the top of the cylinder (diag. 23).
To re-size a cylinder, use a commercially available hone of the proper size. Chuck the hone in a drill press with a
spindle speed of about 600 R.P.M.
Start with coarse stones and center the cylinder under the drill press spindle. Lower the hone so the lower end of the
stones contacts the lowest point in the cylinder bore.
Rotate the adjusting nut so that the stones touch the cylinder wall and begin honing at the bottom of the cylinder. A
light honing oil should be used to lubricate and cool while honing. Move the hone up and down at a rate of 50 strokes
per minute to avoid putting ridges in the cylinder wall. Every fourth or fifth stroke, move the hone far enough to extend
the stones one inch beyond the top and bottom of the
cylinder bore.
Check the bore diameter every twenty or thirty strokes
for size and a 35 o - 45 o crosshatch pattern. If the stones
collect metal, clean the stones with a wire brush when
the hone is removed. (diag. 21).
Hone with the coarse stones until the cylinder bore is
within .002 inch (.051 mm) of the desired finish size.
Replace the coarse stones with finishing stones and
continue honing the cylinder to the final size. Tecumseh
recommends using a 390 grit hone for finishing.
Clean the cylinder and crankcase with soap and water
and dry thoroughly.
Replace the piston and the piston rings with the correct
oversize parts as indicated in the parts manual.
Trenching has been incorporated in the cylinders of the
H50, H60, HHM80, and HM100 series of engines, as well
as the TVM125,140, and 220 models. Trenching improves
air/fuel flow and results in increased horsepower in these
engines. When reinstalling the piston, rings, and rod
assembly in these engines, stagger the ring end gaps
and place the ring end gaps out of the trenched area.
This will prevent the rings from possibly catching the
trenched area and breaking during assembly (diag. 22).
TRENCHING
GAPS
STAGGER RING END GAPS AWAY FROM TRENCHING
21
GAPS
22
INDICATES
.010 OVERSIZE
CYLINDER
23
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