The Specifications of a Honda SL100 Engine

by Kevin Boone

The Honda SL100 was manufactured between 1969 to 1971 with a bore and stroke of 1.988 inches (50.5 mm) and 1.949 inches (49.5 mm), respectively, delivering 11.5 horsepower at 11,000 RPMs. The SL100 operated with a 9.5:5 compression ratio and had a 6.04 cubic inch (100 cc) displacement. The engine displacement gives the motorcycle its name.

Piston and Oil Rings

For the SL100, the piston ring side clearance ranges from 0.0008 to 0.0011 inches (0.025 to 0.030 mm), not to exceed 0.0275 inches (0.70 mm). The oil ring side clearance should be between 0.0059 and 0.0158 inches (0.15 to 0.04 mm), not to exceed 0.0197 inches (0.5 mm). The side clearances for the top and second piston ring gaps range between 0.0059 and 0.0138 inches (0.15 to 0.35 mm), with maximum clearances of 0.0197 inches (0.5 mm).

Engine Valves

The SL100 contains valves and valve springs that must be adjusted correctly for best cycle performance. The intake valve stem diameter should be between 0.2145 to 0.2150 inches (5.450 to 5.465 mm) with a minimum clearance of 0.2130 inches (5.420 mm). The exhaust valve stem diameter ranges between 0.2138 and 0.2146 inches (5.430 to 5.445 mm); it should not be less than 0.2126 inches (5.400 mm). The valve seat width should be between 0.028 and 0.059 inches (0.7 to 1.5 mm). The valve spring length should be 1.406 and 1.591 inches (35.7 and 40.4 mm) for the inner and outer measurements, respectively. The minimum inner length is 1.358 inches (34.5 mm); the minimum outer length is 1.535 inches (39 mm).

Crankshaft and Connecting Rod

The crankshaft run-out for the SL100 engine should range between 0.001 to 0.004 inches (0.03 mm to 0.1mm). The connecting rod clearances range between zero to 0.0004 inches (0 to 0.01 mm) for the side clearance and between 0.004 to 0.014 inches (0.10 to 0.35 mm) for the vertical clearance. The maximum clearances are 0.002 inches (0.05 mm) and 0.0032 inches (0.8 mm) for the side clearance and vertical clearance, respectively.


The SL100 is 75.4 inches (191.5 cm) long, 31.9 inches (81 cm) wide, and 42.9 inches (109 cm) high. It weighs almost 212 lbs (96 kg). The SL100 holds 1.05 qts (1.0 L) of SAE 10-W30 oil. The gas tank holds 2 gallons (7.5 L); it has a 1.25 qt (1.2 L) reserve tank. The SL100 requires a spark plug gap of 0.024 to 0.028 inches (0.6 to 0.7 mm). It uses the type D-8ES (NGK) or type X24ES (Nipondesno) spark plugs.

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