Cylinders - Tecumseh ECV100 - 120 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).
21
22
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