When the Harley-Davidson® Evolution® powered Sportster® was released in 1986 it was obvious that the new engine had a lot of potential. Aside from the obvious benefit of aluminum finned cylinders and a modern cylinder head and valve train, the crankcases were beefed up enough to handle larger bore sizes with far fewer problems than previous engines. The crankcase cylinder deck height was raised to be the same as a big twin engine at 5.375” from the center of the crankshaft, and the cases were stronger in general so that material did not have to be welded on to the sides of the cylinder deck in order to accommodate 3 5/8” bore cylinders. The taller crankcase deck did result in cylinders that were too short to allow a practical stock bore stroker to be designed, so big bore was the only option!
FITMENT
- 1986–'03 Harley-Davidson® Sportster®
- 1994–'02 Harley-Davidson® Buell®
FEATURES AND BENEFITS
- Available in three displacements, for four-speed (1986–’90) and five-speed (1991–’03) models, and in natural aluminum and black powdercoat finish.
- Two displacements available : 89” big bore stroker kit and a 103” monster engine kit
- Requires that the crankcase cylinder spigot holes be bored to accept the larger cylinders
- Complete instructions are provided for this machining operation, and S&S has special tools available that simplify the crankcase boring procedure.
- Made to Order—Get what you want & need
| S&S® Sidewinder® Big Bore Kits for 1986–'03 Harley-Davidson® Sportster® Models |
| Displacement |
Stroke |
Bore |
Compression Ratio |
Piston Type
|
Cylinder Length |
Engine Life
|
Application |
Part Number |
| 79” ** |
3 13⁄16” |
3 5⁄8” |
‡ |
Forged |
Stock |
Stock-like |
1986–'03 |
91-3002 |
89”
|
4 5⁄16” |
3 5⁄8” |
‡ |
Forged |
+.437" |
Very good |
1986–'90 |
91-3121 |
| (5.087”) |
1991–'03 |
91-3123†
|
| CTO |
Specify |
Specify |
|
Specify |
Specify |
|
1986–'03 |
106-5834 |
‡ Compression ratio depends on cylinder head type used. If stock heads are used extensive cylinder head modifications must be performed, making compression ratios completely dependent on final combustion chamber volume.
† 1991 and later engines require conversion to 1986-’90 style pushrod tube assemblies when using adjustable pushrods. S&S kits for 1991 and later engines include a special pushrod tube adapter. Pushrod tube assemblies are not included and must be purchased separately.
** This kit has stock height cylinders and will fit Buell® motorcycles. |
