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Discussion Starter #1
OK, so I thought that my alternator was a bit tired since my voltage likes to hang around 10 volts at idle and 12 volts while driving...

Is it possible that the under drive pulleys are what is causing this?

If I replace the u/d pulley with the original should my voltage jump back up?

Is there anything more involved other than removal of the bolt remove the u/d pulley and replace with the OEM?

THANX

Earl
 

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Earl,

If you leave the underdrive pulley on the crank, then going to the OEM pulley will make things worse.

How much do you idle vs. drive?
 

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Discussion Starter #4
Well I compared the "stock" pulley to the one currently on the alt, which I assume is the steeda u/d pulley...they appear to be VERY close to the same size...I don't have a socket large enough to change it out, as it turns out.

Got a sears gift card....gonna buy more tools :D
 

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Check with the big alternator companies, they usually sell the smaller pulleys.
 

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But!

Check with the big alternator companies, they usually sell the smaller pulleys.
Hello

But we need a bigger pulley! lol

See if your local parts store has one(socket), You need to go there to get a longer belt anyways. Some rebuilt alt's don't come with a pulley, so they swap them.

Paul

ps: I should have a big enough socket. drive accross & we can swap the pulleys. You can see the Niagara Falls while you are here. lol
 

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Another clear as mud post by myself...lol

Hello

But we need a bigger pulley! lol

See if your local parts store has one(socket), You need to go there to get a longer belt anyways. Some rebuilt alt's don't come with a pulley, so they swap them.

Paul

ps: I should have a big enough socket. drive accross & we can swap the pulleys. You can see the Niagara Falls while you are here. lol
Why would you want a bigger pulley? That would spin slower! Remember your 10-speed? When you're pedaling along and going faster and faster (your rear wheel spinning faster), remember shifting to higher gears (the SMALLER ones) on the back? If you wanted to slow down the rear wheel, you shifted to the BIGGER gear in the back.

For the math inclined, let's say he's got a 2 inch diameter pulley now, remember C = pi(D), C=circumferance, D=diameter. So 2 times pi is ~6.28". Say his belt is 32 inches long, that pulley goes around 32/6.28=~5.1 times per belt loop. If you decrease the pulley size to 1.75 inches, 1.75 times pi is ~5.5". So 32/5.5 = ~5.8 times that pulley will spin per belt loop, a 13.7% speed INCREASE. So by putting on a smaller pulley, you make your alternator spin faster (your original should be smaller).

Earl said:
If I replace the u/d pulley with the original should my voltage jump back up?

Is there anything more involved other than removal of the bolt remove the u/d pulley and replace with the OEM?
Yes to both questions! The voltage will go up, but you might have to deal with another issue. With the smaller pulley, your drive belt might be too long - you can deal with that by going to your local parts store and getting a slightly shorter belt.

That's also why when you buy those underdrive pulleys, they slow down the alternator cause they are bigger than stock on the accessories, but smaller on the crank (remember the front sprocket on the 10 speed example - smaller one up front made rear wheel slower if you pedaled same speed). If you read everywhere about u/d pullies, that's the risk associated with them - low voltages especially at night when you're running your lights.

Hopefully that is a little clear..... Merry Christmas!!!
 

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if you have a tuner bump up your idle speed to around 900 rpm and that will take care of all problems with voltage and possible overheating if you dont you can put it in neutral at idle
 
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