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Job 1: Checking & Adjusting Belt Tension
Before we launch into taking things apart we should first see if any adjustment is necessary.
As the Road Star Service Manual points out, the drive belt must be properly tensioned. Too tight, and the belt can stress bearings in the transfer case, making them wear prematurely or seize up, causing great danger. Too loose, and the belt could skip teeth or break, also causing great danger.
Belt tension is usually measured and adjusted with the bike resting under its full weight, although it can be done with the rear wheel suspended, too – just be sure the change in position is accounted for, as described appropriately below.
With the bike upright, the belt and adjustments are more accessible. If you have a helper, they can upright the bike, straddling (but not sitting) on the bike.
If you’re working solo, you can raise the center lift snug against the frame to keep the bike upright, but not actually elevate the frame. If you do this, be very sure the bike is stable. There's a fine line between uprighting the bike while leaving it under its own weight and giving enough lift to keep the bike from toppling over.
If your rear suspension has been lowered, or you have loaded on enough weight to lower the average rear ground clearance, you should consider raising the bike to a position where the centers of the front pulley, the swing-arm pivot and the rear axle all line up. This is the belt's tightest point, and the position Yamaha recommends for adjusting belt tension.
Now it's time to check the belt. There are two accepted ways to measure tension in the belt, and they are both pretty easy to do. The two methods are:
- Deflection -- Which involves pushing up on the lower portion of the belt. Yamaha suggests using a tension gauge, available through them. However, many do-it-yourself mechanics approximate the necessary, 10lbs force by hand.
- Torsion -- Which means twisting the lower portion of the belt with your hand.
Measuring Belt Deflection Using a Tension Gauge
If you have a belt tension gauge, adjusting the belt’s tension is easy and should be accurate. Just put it in position under the belt at the measurement window in the lower belt guard, and measure the deflection. If the bike is under its full weight, the window should read a 7.5mm to 13mm (1/3rd to ½ inch) deflection at 10lbs of force. Tip: If you have the rear wheel is off the ground while you’re doing this measurement, the window should read a 14mm to 21mm (0.55 to 0.83 inch) deflection at 10lbs of force.
Note: The tension reading is found by subtracting the un-deflected reading from the deflected reading.
Note: If your lower belt guard has been removed, as many owners have, the correct measurement position is approximately ½ the distance between the pulleys. This should be very close to the rear of the bend in the lower swing-arm tube.
Measuring Belt Deflection Using Your Fingers
This take a bit of skill, so unless you're confident you can reliably approximate 10lbs of force with your fingers, practice a little before you attempt tensioning your belt.
To practice, find a ten pound exercise weight plate or a 10lb bag of flour or other available 10lb substitute. Practice gauging 10 pounds of finger pressure.
Push up on the drive belt with 10lbs of force in the same location as described in the Using a Tension Gauge above, and measure the deflection.
Measuring Belt Torsion -- Another Option
Instead of deflecting the belt to check tension, many owners twist the lower portion of the belt with their hand, using a moderate force. If you have not previously removed (and discarded) your lower belt guard as a cosmetic or safety mod, your guard must first be remove.
To remove the lower belt guard, just remove the three bolts holding it in place, and work it off and out from the bike.
Grasp the belt with fingers and thumb. Twist the belt using moderate pressure. It's fairly easy to get the right twisting force. Just steadily increase your twist until you reach a point where it takes considerably more force to twist the belt very little more. Then back off just a bit.
Your grasp should be done approximately half way between the pulleys.
The belt is correctly tensioned when it twists about one quarter turn, as shown in the photo above.