What belt?

[craigvwdude]

Fellas,
when doing the suby conversion, what alt. belt is everyone using when eliminating all other accessory's? I'll be just running the alternator.
thanks!

[panel]

Craig , I've eliminated the factory adjuster and went with a simple heim joint set-up. You can see it in an older vid.

Belt info: Dayco 5050290. Not sure it'll work for your length but might get you in the ball park.

https://www.youtube.com/watch?v=BO3r-OkzGtA

About 0:24 sec's in.

[GS guy]

Alternator in stock position using the non-AC alternator mount: AC Delco 5K275

Mock-up1.JPG

[Ol'fogasaurus]

If possible I would add an idler pully to that mainly because the upper pully is so small so the contact area is tiny.

Lee

More info: remember, as the RPMs increase the belt will be thrown out into more of an arc/to the sides more and more (mass causing it) as the RPMs get higher. One of the reasons you usually seen them on high powered cars. https://www.bing.com/search?q=idler+pul ... dd80dbe720

[panel]

Ol'fogasaurus......but the factory never had one ?

[Ol'fogasaurus]

Ol'fogasaurus......but the factory never had one ?

The way that a belt works for water pumps and generators/alternators has always been a problem especially as the RPMs go up. The belt has a mass to it; if you swung a bucket of water on a rope as you swung it faster you can feel the mass want to move away from the origination of the action... being you. As the belt wants to swing out the contact area of it on the pullies gets smaller.

Maybe this is better: https://www.bing.com/search?q=how+does+ ... a0e8982d77

https://en.wikipedia.org/wiki/Pulley

Page down to the belt and pully system

In your case I would suggest that the idler pully pushes the belt towards the center of the two main pullies giving both of them more wrap-a-round contact with the belt and the idler pully.. I can draw a pix if you want.

Lee

[panel]

No need for pics I'm a Millwright. It was just an observation that the Japanese engineers thought it was fine without one. I love and learn from your explanations......it's no disrespect it was just curiosity etc.

[Ol'fogasaurus]

Lee

[ajdenette]

Lee I would agree with Panel as you have almost 50% on the alternator and almost 50% increase from the roughly 25% in the Subaru (or Vanagon with power steering) so I don't believe in this case an Idler is necessary also remember that these are serpentine belts with I believe 5 groves so a lot more surface area than an older V grove belt system.

[Ol'fogasaurus]

Lee I would agree with Panel as you have almost 50% on the alternator and almost 50% increase from the roughly 25% in the Subaru (or Vanagon with power steering) so I don't believe in this case an Idler is necessary also remember that these are serpentine belts with I believe 5 groves so a lot more surface area than an older V grove belt system.

Re-write but not too sure how good it is:

A belt has mass to it so the faster a pair of pullies rotate the weight/mass of the belt affects how it sits/contacts on the pullies.

Draw two circles and then join the arcs of the circles at tangent points on each side of the circles with a straight line; mark the contact points on the pullies.

When you rotate the pullies, e.g., change the speed of the rotation of the engine the belt, the straight line going from the one pully to the other pully changes from a straight line into an arc (mass/weight). So, as the RPMs get higher you now have an arc on each side of the pullies that will enlarge as the RPMs get faster, this is what you are now dealing with.

The faster the rotation the sooner it wants to join/leave the pullies in different locations than when the engine was static giving the belt a smaller contact area on the pullies. Adding a secondary adjustable ((Idler) pully, usually, to one side can off-set some of the arc's loss of contact area to the pullies by pushing the belt more towards the center line of the pullies, off-setting some of the weight the speed of the belt is throwing around.

Now draw a slight arc to each side of the pullies joining them at the tangent of the circles and the arc and again mark the contact spots. Notice the contact patch is now smaller.

Wear and belt age also come into play.

This is one of the problems that the old Corvair engines had where the belt also had a 90° turn from the crank pully to the fan pully on top of the engine.

"Idler pullies" https://www.bing.com/shop?q=idler%20pul ... 3508AF0DC7

Lee

If you look at blower belts, they have "teeth" going across the wide belt that fit into reliefs on the crank and blower pullies as the loading on the belts is so great that the belt can slip or break. This is kind of what my original introduction to the problem was; "Chugga, chugga" to "varoom" was the introduction.

[Ol'fogasaurus]

I did a rewrite on this trying to make it clearer but not sure if it has.

Lee