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Alternator - options & opinions?

The car is a 2000 Toyota Camry XLE with V6 motor, auto trans, 187K miles. The car dies with my wife driving and won’t restart in the supermarket parking lot. Typical low charge battery, some dash lights and clicking when you turn the key to activate the starter. Troubleshooting leads to a bad alternator.

I get an alternator from my trusted NAPA store (remaned unit) and it looks like the right one. I swap the new one in the car and all goes fine until I tighten up the serpentine belt. I run out of travel on the tensioner and the belt still has too much slack in it. I start the car anyway and get the belt squeal I expect and shut it down immediately. I spend a few minutes rechecking everything and it is a puzzle? I get my tape measure out and find the problem - the old alternator has a 2 3/4" pulley, and the new one measures just 2 1/4". A full 1/5" smaller diameter pulley.

I consider changing the pulleys, and consult my car savey electrical engineer brother who says the pulleys are a bear to remove and it is not a good idea. Plus, the two alternators are going to spin at significantly different speeds. Next I call NAPA and they will order in another alternator, which should come with the correct sized pulley, but perhaps not. The replacement won’t be available for several days due to the upcoming weekend. I have other cars so I can wait.

The plot thickens, perhaps the old alternator isn’t the OEM alternator. I remember my son had starting problems when he had this car at college and I believe the result was a new alternator some 4 to 5 years ago. Can anyone confirm for me what the OEM sized alternator pulley really is for this car?

What are the pros and cons of just putting a smaller serpentine belt on the car and using the newly installed alternator? It will be spinning faster than the one that came out of the car, the pulley is about 20% smaller. Will this 20% difference result in overcharging? Will it put the alternator rpm’s out of the design range and shorten the life of the bearings? These are the possible con’s I can think of. The main pro is a new belt will go on in a few minutes and I’m in business. Otherwise I wait a few days and have to swap alternators again.

Would a pro mechanic just put on a new belt to satisfy the customer who is without a car, or tell the customer the part was incorrect and a new one will be on the car in a day or two?

So, that’s the story. Are there other options I’m not considering? Opinions on whether the new alternator is OK to go with a smaller serp belt?

Choose to resize the belt…or replace the pulley…Neither is difficult. Id venture a guess whomever installed the non stock alternator made a belt change to accomodate this…or visa versa…you are just dealing with the aftermath.

Make sure the replacement alternator is the correct unit with correct pulley and then modify the belt as needed. You may find that if you ask for a new stock belt…it goes on fine with your new setup because the new belt you ask for is the correct size to accomodate the pulley size on the new alternator…that has the proper size everything…

Either somebody at some point made a change and kept it to themselves…or you have the incorrect new part. Its either or really…more than likely…you have the wrong new part…but either scenario is possible.

Just ask the dealer what the stock pulley size is for your vehicle…they change them for various applications. No telling who did what or which… Either someone changed belts…or you got the wrong pulley installed on the correct alternator type…or the wrong alternator type alltogether. Since all parameters are changeable…no scenario presents too much trouble really… Changing pulleys is a piece of cake.


This Is One Reason I Choose A Local Auto Electric Shop To Rebuild (Usually While I Wait) What I’ve Got. It’s Child’s Play For Them And They Stock The Parts.

The Other Is Cost. They’ll Do It A Fraction Of The Unit Replacement Cost.

I suppose you don’t have the core (old unit)? You could see if you are fortunate enough to have a local Auto Electric Shop that would rebuild it, and how quickly, and at what cost.

No offense intended, it’s an old car (I have some older than that). Another option is the old salvage yard. Most will warrant the alternator to work.

Some cars (like my '81 Accord) could come with different size alternator pulleys, depending on if they had AC or not.
The smaller pulley spins the alternator faster at idle so it could deliver more current to keep up with the added load of the AC components.
The larger pulley reduces drag on the engine slightly.
A 20% smaller pulley will not affect how the alternator charges.
It’s regulated to work over a wide range of speeds. After all, the engine can run from <1000 to ~6000 rpm.

I’d buy a new stock belt and see if it fits, or just take the current belt to the part store and see if it matches the new one. Or check the model number on the current belt. If the current belt is non-stock, problem solved.

Update - I just got back from NAPA. I took the old alternator and the serp belt to the store to get some more info. The serp belt is the proper belt for the V6 but the alternator was not the OEM unit.

A guy was shopping at the store said he had worked for Toyota and suspected the smaller pulley would be for a 4 cyl. Also using the smaller pulley on the V6 would “fry” the electrical system.

Then a NAPA guy took off the old pulley with an impact wrench. My job now is to see if I can get the pulley off the new alternator while it is installed on the motor. If not I’ll have to take it off car and back to the NAPA store and they will make the switch. The tricky part will be keeping the pulley from moving when I apply the torque needed to get the nut loosen up.

Thanks for the replies, I have a plan of attack now.

Shouldn’t “fry” anything… But anyway…good news…you have this handled

Also using the smaller pulley on the V6 would "fry" the electrical system.

No, just NO. Sure the pulley spins faster but it has a regulator that prevents over-voltage. The extra amperage doesn’t even get made unless there is enough load. So it wouldn’t “fry” the electrical system. Its about having enough capacity for current not about having too much.

And you learned a very good DIY lesson, the parts stores don’t always supply the right replacement parts even though the “computer” says that is the correct part. Save the old one to compare or swap pulleys just in case. Yeah its a 2nd trip to the parts store but beats not getting your car fixed.


Wrong pully return and get the right part, no need in my opinion to try and fix an incorrectly supplied part. Your tensioner might need replacement also.

Me, I’d just return the alternator with the wrong size pulley and ask NAPA to order up one with the correct size. In the meantime I’d drive another car. If NAPA isn’t able to do that for some reason, my next choice would be to have the local auto electric shop rebuild the first alternator. Hopefully you haven’t turned it in for the core return yet.

In theory – by “theory” I mean the laws of physics – the alternator should still work with the smaller pulley. But here’s the thing: Alternators and the associated voltage regulator are designed to operate on a certain rpm range. If you exceed that range, either too high or too low, there’s no way to predict what will happen. There’s voltage limits, current limits, and heat considerations, all taken into account when they select the wire size for the coils and number of turns. The engineer who designed that alternator would be able to venture a guess what happens outside of the rpm specs, but I doubt they are available for asking.

This is a case where waiting will save you a lot of time I expect.

Maybe they’re better now but fair warning, I never had a NAPA alternator that lasted much more than a year or two, rebuilt or new. I finally just gave up on the warranty and went with Delco. Problems ranged from dead to erratic voltage fluctuation.

I would replace the alternator with the correct one tomorrow. Being told that the correct one is several days away is ridiculous. My local supplier has 2 reman and one new on the shelf and 2 more at other local stores. I would have your NAPA store have one delivered to them in the morning so you can exchange it. Several days for a Camry alternator…are you in a different country?

Update 2 - I was able to remove the small pulley and put the larger one on. Got a good voltage reading and all seems OK. I’m not real pleased with NAPA, but they did assist in getting it right eventually. Just the whole job took a lot longer to complete.

The biggest problem I had with the pulley switch was holding the larger pulley still while I got enough torque on the nut to tighten it. The channel locks worked to get the smaller pulley off, but the larger one was too big for the channel locks I had. I found some vice grips and a way to wedge them against the radiator support that worked.

I’ll do some more voltage checks later today after I drive the car around doing erands. But I think we are done with this thread. Thanks all. Uncle Turbo

Glad you got it resolved Uncle Turbo. Good for you for sticking with it.

Call around to other auto parts suppliers. Any one that has much of a shop will have the tools to replace the pulley. It is no big job.

I presume that when your son had the had the starting issues the wrong pulley was installed and then they had to go with a different belt also…

But you could;
Take the old belt to the parts store and they can measure it, or cross reference the numbers on the belt. Then sell you one that’s shorter.

It will not cause over charging.


common sense answer: We have an Auto Electrical Shop that has been in business long before I was born (I’m 64 y/o) I have used them several times with outstanding success! Yes they will repair/rebuild components very quickly while you wait or even observe. I have had a Ford big block dual point distributer rebuilt (New bushings, points, condenser, ground wire). Points even had dwell set. ($15) Several starter motors, generators, and alternators repaired. None over $10! They test, repair, then re-test while you watch (if you desire). I’m very sad businesses like this are disappearing. My trusted independent mechanic shop has been in business (still family owned) since 1924.

Rebuilding alternators for $10 and distributors for $15 is a sure way to go out of business. You must be referring to prices 50 years ago, this if not relevant today, will only make people feel as though they have been cheated by buying a rebuilt unit.

Have to agree the Alternator ,itself should not overcharge anything ,if the belt works then the pulley should be correct for the unit (you can buy underdrive pulleys that put less parasitic powerloss on the engine (I imagine the charging rate is a bit slower though.)
I assume you routed the belt correctly ?

"Rebuilding alternators for $10 and distributors for $15 is a sure way to go out of business. You must be referring to prices 50 years ago, this if not relevant today, will only make people feel as though they have been cheated by buying a rebuilt unit."

I can’t speak for @sgtrock21, and his prices, but as I have pointed out I recently have had work done at a local Auto Electric (family run) business at a fraction of the cost of a rebuilt unit from an auto parts store.

The building that houses the business is off the main street and not much to see. It’s probably been paid for years, they don’t advertise, and I’m sure the “overhead expense” is quite extremely low. Also, it takes them only minutes to overhaul a component.

They once rebuilt an alternator for me that was actually could not be rebuilt because brushes were not available. When they have downtime at this shop they make brushes that fit these units and stock them.

Just as Sgtrock experiences, my local shop bench tests components before and after repairs, usually while you wait or watch. You can pet the friendly dog, too.

Since I’m the one who brought up local Auto Electric shops, I’m sincerely sorry if anybody is offended or feelings hurt by this sort of thing. That is not the intent.

The intent of discussing this is to have people check and see if they have a local shop like this or one not too far distant. I know of at least two within a reasonable drive from my very rural location.