What size &; threads are the 3 holes in 2001 buick lesabre 3.8 harmonic balancer?

This is the bolt, but the answer is the size of the socket that fits it. If you don't have a full set of sockets and wrenches, doing job is impossible. If it is oversize, and I don't think it is, you can get larger specialized tool from Autozone for free and just a small returnable deposit.

https://www.google.com/search?q=2001+Buick+Century+Custom+harmonic+balancer+bolt

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Using a standard harmonic balancer puller with 3 bolts that are just a bit too large for the 3 openings if possible., Tap them with a die large enough to get a decent grip with the bolts and remove it like any other. If that won't work then just drill and tap 3 holes for the remover. I generally use 10 MM bolts when I do mine.

The crankshaft sensor is located behind the harmonic balancer. There is a special tool you can rent/loan from your local auto parts store in order to remove the harmonic balancer. Once it is off 2 bolt hold the crankshaft position sensor in place. Note there could be many other factors causing your engine to stall or not restart; but those crank sensors do tend to go out on those engines.

it is located behind the harmonic balancer. you will need a harmonic balancer puller

The outer ring should not move independently of the inner pat of the pulley. If it does the rubber isolator in between the two parts is bad and the pulley will need to be replaced. The pulleys are common to fail and you can usually get them from your local parts store or a gm dealer. The center bolt should be a 15/16" . You may need an impact wrench to remove. There will be a couple of threaded holes in the pulley. You will need a pulled and bolts to remove the pulley. A steering wheel pulled works really good for this and you can find the bolts at your local hardware store. I'm pretty sure they are 6mm holes but I do not remember the thread pitch. It's a pretty simple job and the worst part will be getting the crank bolt loose.

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The harmonic balancer is at the very bottom of your engine. There is a pulley attached to the front of it that runs all your belts. You will need a socket and breaker bar or possibly an air gun to remove the center nut that bolts it to the crank. It will be an odd size socket that won't come in a regular socket set and you would be better off using 1/2 inch drive instead of the regular 3/8. You will also need to get a puller to pull it off the crank. The balancer is 2 pieces os steel with a piece of rubber between them so a special puller that bolts to the inner part is what is needed.
The easiest way to get it off would be to let someone else do it for you. You will kill the best part of an afternoon doing it yourself at home. Pay close attention to how your belts line up before you remove them. Hope this helps.

You remove the giant bolt, then you use a harmonic balancer puller, which essentially bolts up rather than using claws to grab. The bolts of the puller go into the pulley fastening bolt holes.

Something must happen to protect the crank threads, a spacer, using the retainer bolt, or whatever, just do not kill the threads.

you will need sockets,the crank bolt i belive is 22mm and you might need in impact wrench to remove bolt. the crank sensor is 1/2 in or 13mm, that a rachet is good.and to remove balancer sometimes youll need a puller. hope this helps.

National fine thread, regular right hand. You may need a puller to remove damper after removing bolt.

i had used three bolts they have to be 6mm thik and like about 6 inches long then you install some flat washers by the head and use a regular crank pulley remover, you'll see three little holes inside the groevs at front side of pulley and there is where you install the bolts