Another Alternator Belt Tensioner - 3VX belts?

[coke]

Did you get the right thread bolt? I don't know what it is off the top of my head, but I always go to the bolt store and find a nut that fits on the old bolt and then pick out a bolt with the same threads and spacing as the nut.

[tylernt]

Does anybody know what RPM the alternator turns at? At redline, 5,000 engine RPM (10,000 crank RPM), the alt might see what -- 20,000RPM if the crank:alt pulleys are 2:1 in size? I need to do this mod on my Jetta and want to make sure I get a bearing that can handle the speed...

[TylerDurden]

I bought the two bearings and the set of five bolts from Grainger Suppy and found the bolt to be very difficult to thread in completely. I have an inch of the head bolt unable to thread all the way in. I even tried using a breaker bar, the bolt threaded in nicely early on but gradually became impossible to tighten all the way in. I did manage to have enough bolt to add the two bearings and a nut with a washer. Hope it fixes my problem, any suggestions of why the bolt would not thread all the way through?

I cut more threads to get the bolt completely through. See the second picture comparing the threads.

@tylernt,
IIRC, tach 5K is crank 5K... the alt may run at 10K. The Grainger bearings are rated 16K.

[Fatmobile]

Might want to run a die down the bolt.
Might want to chase the bracket threads too,
a piece of metal might have broken off the bolt thread and jambed in the bracket threads.

[coke]

I just remembered that on my car the alternator bolt (the big one) is tapered at the end, and I do believe you may have to run a tap through the bracket. Not 100% sure, but I'm almost certain at least the bolt is, and the end of the threads in the bracket is tapered down.

Sorry for my highly unautomotive terms. Hope you understand what I'm saying.

[TylerDurden]

Does anybody know what RPM the alternator turns at? At redline, 5,000 engine RPM (10,000 crank RPM), the alt might see what -- 20,000RPM if the crank:alt pulleys are 2:1 in size? I need to do this mod on my Jetta and want to make sure I get a bearing that can handle the speed...

Now that I have some coffee, I have a few more thoughts:

1) The alternator rpm is not too important; the diameter of the bearings compared to the diameter of the AC pulley is.

2) The bearing has very little load, <5lbs perhaps.

3) The stock idler pulleys use similar bearings, nothing fancy AFAICT.

[diesel freak]

Now that you mentioned it I noticed on the remaining bolts in the bag that there seems to be not enough threads. Can I add threads to an existing bolt or can I just buy a bolt with more threads? I have never used a die before, would I need to take the bolt to a machine shop or is is something that I could easily do myself?

[TylerDurden]

I would not use a full-thread bolt, the threaded section will be weaker and have a sloppy fit (narrower diameter).

Adding threads is easy, the tools are cheap. (A good addition to your growing VW DIY arsenal.) You will also need some cutting oil.

Hold the bolt in a vise if you have one
Oil the threads
Put the die in the handle.
Spin the die down the existing threads, the die should have the wider opening facing the head of the bolt
When the die starts to bind, turn it 1/2 turn, then back to clear the chips. Use a small tool to clear the chips if needed
Add some more oil at the die
Repeat until you have enough threads.

(Surprisingly, I found no good youtube videos.)

[diesel freak]

Well I bought a Tap & Die 10mm and it was a piece of cake to extend the threads with the die. The hole was all buggered up from my previous attempt to thread the non threaded bolt all the way in. I fixed that with the 10mm tap. The only difference is that I threaded the bolt from the belt side in to the motor compartment side so that now the bearings spin on the smooth bolt instead of the threads of the bolt. Now I hope that fixes my alternator belt problem, I drove around the block and the alternator was charging and no more squealing, only time will tell. Thanks for all your help.

[TylerDurden]

Sounds promising, keep us posted.

[MagicBus]

Awesome writeup. I actually NEED to try this on my '90 Jetta diesel. Been eating too many belts.

I have a question on your second photo:

Forgive the simplistic question. I don't see an explicit mention of it, but it looks like you ADDED some threads to the bolt? How did you do that?


EDIT - I missed the second page of this thread where you discuss using the die. Thanks - question answered.

[tylernt]

Forgive the simplistic question. I don't see an explicit mention of it, but it looks like you ADDED some threads to the bolt? How did you do that?

Using a die, thread it on to the existing threads, then just keep right on turning and it will cut new threads into the blank area. Use lots of cutting fluid!

[MagicBus]

Forgive the simplistic question. I don't see an explicit mention of it, but it looks like you ADDED some threads to the bolt? How did you do that?

Using a die, thread it on to the existing threads, then just keep right on turning and it will cut new threads into the blank area. Use lots of cutting fluid!

Got it. Will I need a metric or SAE tap and die set?

[TylerDurden]

Will I need a metric or SAE tap and die set?

Best to use metric: 10x1.5

In photo #2 you can see the new bolt, another new bolt with added threads and lastly, an original bolt where the anti-sieze indicates the amount of additional threads needed.


Keep us posted...

[MagicBus]

Will I need a metric or SAE tap and die set?

Best to use metric: 10x1.5

In photo #2 you can see the new bolt, another new bolt with added threads and lastly, an original bolt where the anti-sieze indicates the amount of additional threads needed.

Keep us posted...

Will do. I actually looked at that photo a few times before I realized that was the intent - i.e. to show "the new bolt, another new bolt with added threads and lastly, an original bolt where the anti-sieze indicates the amount of additional threads needed."

I just ordered from Grainger and will source the nuts/washers locally. BUT, when I get my Grainger bolts I'm going to see, first, if I can't match it with an off-the-shelf bolt with the correct number of threads, thus eliminating the need for the die.

Incidentally, the prices have gone up. I'm paying $16.78 a pop for the bearings and $11.84 for the bolts (as of 2011-02-10, ordered online to ship) plus shipping (not available in local stores). So, total is closer to $60 for me. Still worth it if it eliminates this hassle.

How's your setup holding up?

For what it's worth, I was referred to this thread by someone over on VWVortex. They also showed me a link to THIS page:
viewtopic.php?t=8173

Latest posts in the above thread indicate a failed belt. My guess, from looking at the photo there, is the extreme backbend in the belt over the brass roller contributed to this. I like the look of your setup because a) it keeps the stock tensioner in place, and b) doesn't introduce any new harsh bends.

Additionally, it looks like the stock tensioner will now be placing less stress on the belt, as the new roller will take up some slack.


Will be a few days at least before I get this stuff and can install it. I promise an update plus a rolling update on how this works for me.

And, just for giggles and viewing pleasure, here's my thread on VWVortex:
http://forums.vwvortex.com/showthread.p ... -GL-diesel