Alternator Belt Shredded? Why?
05-24-2019, 01:18 PM
#16
Rennlist Member
I think I had the belt way too tight. I loosened up the tension a good 1/2" so the tensioner looks like this now.
After adjusting the belt I took it out and ran it much harder for longer time There has been no further degradation of the belt . There was less than 5 min of driving at low engine speeds and I could hear the belt making noise as the part that broke loose was hitting things.
I'll be watching the felt-like surface of the belt in the next few days for signs of slipping after installing a new one (shiny). If nothing develops then it was me over tightening and I'll be more careful to keep the tension in the right area...thanks for the input as always everyone.
05-24-2019, 01:25 PM
#17
Rennlist Member
That lifted edge on the ribbed belt is almost always caused by misalignment of the pulleys. Lining up the pulleys perfectly includes a good straightedge, and a couple measurements to account for thicknesses of the pulley outer flanges. Severe misalignment on ribbed belts usually causes the belt to wear on the edges like that before delaminating.
Other possible causes include poor installation, where a belt might accidentally be installed one rib off on one of the pulleys.
Required tension on the alternator belt is a lot higher than most folks realize. The literal 'rule of thumb' for this belt is the ability to deflect the belt no more than one belt thickness at mid-span with thumb pressure. That's really tight, like guitar-string tight. IIRC the WSM has a target setting to use with the 9501 tool, great guidance if you have access to that tool. Full tension is a requirement with the relatively small diameter and contact area of the alternator pulley. With the GB alternator shown in the pictures, the tension requirement is likely even more acute, as you consider the extra energy conversion available in the premium part. That energy comes from the crank and is transferred via the belt. At full load, somewhere between four and five horsepower is needed with Greg's alternator, all transferred over the couple inches of contact area on the alternator pulley. The bearings in the alternator are sized to carry that belt tension load, of course. Greg may have additional guidance on this, based on his and shared customer experience.
Other possible causes include poor installation, where a belt might accidentally be installed one rib off on one of the pulleys.
Required tension on the alternator belt is a lot higher than most folks realize. The literal 'rule of thumb' for this belt is the ability to deflect the belt no more than one belt thickness at mid-span with thumb pressure. That's really tight, like guitar-string tight. IIRC the WSM has a target setting to use with the 9501 tool, great guidance if you have access to that tool. Full tension is a requirement with the relatively small diameter and contact area of the alternator pulley. With the GB alternator shown in the pictures, the tension requirement is likely even more acute, as you consider the extra energy conversion available in the premium part. That energy comes from the crank and is transferred via the belt. At full load, somewhere between four and five horsepower is needed with Greg's alternator, all transferred over the couple inches of contact area on the alternator pulley. The bearings in the alternator are sized to carry that belt tension load, of course. Greg may have additional guidance on this, based on his and shared customer experience.
Hey Dr. Bob thanks for contributing; I had not thought of the misalignment issue..of course it looks even but that doesn't mean it is.
Maybe a funny question but is there a rule of thumb that says if the belt is deteriorating on the edge against the alternator does that mean the pulley is too far out/in?
Also just confirming if we need to make an adjustment would we remove the front pulley and place a washer behind or move the whole alternator?
Thanks!
05-24-2019, 03:08 PM
#18
Rennlist
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1. Continental belts are very elastic and inferior to the factory belt. This is why we send a brand new factory belt with our new alternators. Because Continental belts are elastic, it is very difficult to get one to factory specified tightness....they simply stretch and start breaking the internal fibers, before they get to the factory recommended tightness. It is easy to ruin one of these belts during installation, because of this.
Factory belts will very rarely need any further attention for 15,000 miles, when correctly tensioned. This is why we exclusively use factory belts....we have extremely low problems (except occasionally with early cars with "V" alternator belts.)
The factory recommended tightness is amazingly tight. It is very doubtful that any non-professional would overtighten one....the problem is almost always undertightening.
2. As mentioned, check your belt alignment, although this is very rarely an issue on a late model 928. The alternator alignment is perfect for these cars. If you have an alignment issue, it will be with the drive pulley.
3. Make sure that the drive pulley is straight. We replace an amazing amount of these pulleys, ruined in timing belt changes. People will do some amazing things when they do not have the special tools needed to get the crankshaft bolt loosened and retightened. Start the car and watch the pulley. There should be zero "wobble" in any of the pulleys.
4. Alternators are designed for use to maintain batteries, never to charge low batteries. Full alternator output for extended periods of time will quickly overheat/ruin a belt. Check your battery condition and state of charge. If your battery is consistently drained after sitting overnight, find and repair the current draw. If the car sits for more than 3-4 days, buy and use a trickle charger.
Factory belts will very rarely need any further attention for 15,000 miles, when correctly tensioned. This is why we exclusively use factory belts....we have extremely low problems (except occasionally with early cars with "V" alternator belts.)
The factory recommended tightness is amazingly tight. It is very doubtful that any non-professional would overtighten one....the problem is almost always undertightening.
2. As mentioned, check your belt alignment, although this is very rarely an issue on a late model 928. The alternator alignment is perfect for these cars. If you have an alignment issue, it will be with the drive pulley.
3. Make sure that the drive pulley is straight. We replace an amazing amount of these pulleys, ruined in timing belt changes. People will do some amazing things when they do not have the special tools needed to get the crankshaft bolt loosened and retightened. Start the car and watch the pulley. There should be zero "wobble" in any of the pulleys.
4. Alternators are designed for use to maintain batteries, never to charge low batteries. Full alternator output for extended periods of time will quickly overheat/ruin a belt. Check your battery condition and state of charge. If your battery is consistently drained after sitting overnight, find and repair the current draw. If the car sits for more than 3-4 days, buy and use a trickle charger.
05-24-2019, 11:59 PM
#19
Rennlist Member
Greg out of curiosity what amount of tightness in belt units does your alternator require? The factory alt requires 9.2 for a new belt and 8.4 for a used one IIRC.
05-25-2019, 03:21 AM
#20
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