Easyrider’s Award for ‘Performance Product 2005’

Sputhe has been a leading manufacturer of high performance motorcycle engines and transmissions for more than 28 years.  Tying the two components together is a logical progression.

As with other Sputhe products, our primary drive system is a totally engineered assembly of matched components.  After carefully studying and rigorously testing the primary drives currently available, we designed a unit that would handle today’s super large displacement high torque engines without excessive width and the complexity of outboard bearings.  We have substantially increased the capacity of the clutch and incorporated the latest belt technology.  We are the only manufacturer to use two inboard ball bearings on our clutch basket to maintain perfect belt alignment.

Our outer belt cover is machined from a two and one half inch thick, forty-seven pound aluminum billet.  The inner housing begins as a twenty-seven pound billet.  The finished assembly weighs only eleven pounds or five pounds less than a stock Softail housing.  This vented housing completely encloses both the inner and outer surfaces of the belt to protect the rider as well as the belt.  Our unique “enclosed open center” design prevents debris from becoming trapped between the belt and the pulleys.  The spans between the pulleys are essentially two box sections joined to a cylindrical section at either end and rigidly bolted to the billet inner housing.  This design results in an extremely robust unit that combines simple timeless styling with extreme narrowness and lightness.

Our clutch has nine Kevlar and steel plate sets with over 200 square inches of friction surface.  It is housed in a hard anodized 7075-T6 billet aluminum clutch basket.  This is one of the strongest non-lockup clutches made, yet it has a light pull and smooth engagement because it uses a diaphragm spring instead of coil springs.  The engine pulley hub is machined from chrome-moly bar stock.  No cast or extruded engine pulleys for us.  Our pulleys are machined from 7075-T6 aluminum billet for the highest possible strength to weight ratio and they are hard anodized for long life.

We have specified a 50mm wide Gates GT-2 belt, which is much stronger than the belts used by most of our competitors.  We have also altered the primary drive ratio to make starting easier and increase road speed while reducing engine vibration and transmission gear loading.

The Sputhe primary drive is currently available for Evolution Softails only.  You may specify either a show polished or a machined finish.  We will be producing units for other models in the near future. 

Comparison of a stock Harley-Davidson Softail primary drive assembly
and a Sputhe primary drive assembly





Front Sprocket/Pulley

6.0 pounds

2.6 pounds


3.3 pounds

0.8 pounds

Clutch Assembly

13.7 pounds

12.5 pounds

Starter Pinion Assembly

0.9 pounds

0.4 pounds

Inner and Outer Housings

16.1 pounds

10.9 pounds

Chain Tensioner

1.7 pounds

0.0 pounds


41.7 pounds

27.2 pounds



Part #8800 $

a -

Zero and 1 ” offset (inquire about other options)

b -

Optional oil filter

c -

Use any cone motor ignition cover

d -

Exclusive double bearing “Cush Drive Front Pulley”

e -

Hard anodized 7075-T6 billet clutch basket

f -

Easy pull diaphragm clutch

g -

200 square inches of Kevlar clutch surface

h -

Inboard support bearing on offset models

i -

Inner belt run is totally enclosed






E-Mail: sputhe@hotmail.com

Tel: (530) 268-0887
11185 Lime Kiln Road
Grass Valley, CA 95949-9715

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SputheEngineering, Inc. ©1997-2013.  All Rights Reserved.