Maintenance and belt alignment of the Vanguard Hovercraft 40hp “Carbon 90” drive.
The drive system consists of the Kohler ECV-980 engine, direct drive lift fan, a set of idlers, a belt and the propeller. The system utilizes a synchronous Gates Polychain carbon fiber belt to prevent drive slippage and reduce maintenance. The belt tension is set at the factory and need not be altered unless bearings or the belt are changed. A sonic belt tension meter is used to ensure precision belt tension. Many smart phones can be used to set the tension at the 70-75 hz that is required. The drive system features double sealed bearings to ensure long life in the marine environment.
Read all the way through these instructions before doing anything.
Belt tension is very important as too little tension can result is jumping teeth and premature belt failure. Over tension can result in bearing failure and or the belt. Tension can be checked most accurately by sound. Pluck the belt at the mid span of the vertical section up to the prop pulley. Listen to the sound with a smart phone running the tension2Go app on a smart phone, laptop computer and guitar tuner. The proper tension for a new belt is 72-75 hz, used belt 68-72 hz. Equally as important is drive alignment. This includes both angular and parallel misalignment, though this is a bit more complicated in the case of the right angel drive system.
Initial alignment is accomplished using a straight edge to observe the alignment of the idlers pulleys to the engine and prop pulleys. The hovercraft belt and the straight edge should appear to be parallel as the head toward the engine or prop pulley. Some experience is required to interpret this as the belt is twisting. This would be an angular alignment, the parallel alignment is controlled by the jacking screw, pictured below. Watch the tracking on the engine pulley to check the jack screw setting. The engine can be rotated by hand by pulling the belt with the spark plugs removed to check the progress of the adjustments.
The other parallel alignment is to the prop pulley, but since there is no direct adjustment for this, the prop shaft is tipped, fore or aft to adjust tracking on the prop pulley.
During all these adjustments belt tension must be checked to ensure the belt does not get to tight. Tipping the idlers for example changes the tension significantly. As you zero in on the alignment the prop shaft can be raised to set the final tension.
Once the pulley and tension is set using the above procedure the system is tested with the prop removed. Care must be taken to insure all tools and objects are clear before running the system at idle. The alignment can be observed by watching the belt at all points, engine pulley, left and right idlers and prop. The belt should not ride hard against a flange or near the edge of the prop pulley. The optimal belt setting should however track towards the left on both the idlers as it moves right under higher power setting.
The alignment can be fine-tuned at idle with a 9/16” wrench provided great care is taken to keep tools and fingers out of the moving lift fan and belt! The prop should not be on at this point.
Once everything is fine tuned, the hovercraft belt tension is given a final check.
Next the 76″ 3 blade hovercraft prop can be installed and tightened to 185 in lbs. Use Loctite and primer. The propeller pitch needs to be set at about 23°, measured at a point 3/4 the way from the center along the blades length. An electronic protractor is helpful here, though some phone apps can do this too.
If the fan was removed the torque on the center bolt is 40 ft/lbs. The six 3/8-16x.75 fan hub bolts are tightened to 20ft/lbs (Use Loctite and primer).
Note: The rudder bar assembly can be easily removed to aid in this work. Disconnect the steering cable, lower bolts and upper bolts. You must use Loctite and primer to reinstall the upper bolts.
Note: Loctite® threadlockers are single-component adhesives that cure in the absence of air and in contact with active metal to form a tough thermoset plastic. They completely fill all voids between the interfacing threads, which makes the assembly a unitized component and ultimately prevents loosening.
When assembling metal parts with inactive surfaces, Loctite® primers are recommended to ensure proper performance of Loctite® threadlockers. When assembling inactive metal parts, which are low in metal ions, the use of Loctite® primers is recommended to ensure proper performance of Loctite® threadlockers.
*Inactive Metals (Primers Recommended)
|· Plated Parts||· Silver|
|· Anodized Aluminum||· Gold|
|· Titanium||· Inconel®|
|· Stainless Steel||· Magnetite Steel|
|· Galvanized Steel||· Natural or Chemical Black Oxide|
|· Zinc||· Magnesium|
|· Pure Aluminum||· Cadmium|
Active Metals (Primers Optional)
|· Iron||· Plain Steel|
|· Bronze||· Manganese|
|· Monel®||· Kovar|
|· Copper||· Brass|
Primers: LOCTITE 37509 Klean ‘N Prime Anaerobic Activator Aerosol Can – 4.5 oz.
Loctite 21348 Primer 7649 4.5 Oz Aerosol Can (Acetone)
Permatex® Surface Prep Activator
Please ask questions as they arise if you are unclear, for your safety, and proper Vanguard hovercraft function.