What size bolt is the top bolt to a alternator for a 1999 suzuki esterm

Whatever part number the parts book calls for, it is sold by part number not by pulley size, that is not listed.

Disconnect the negative battery cable.
Loosen adjusting bracket nut or bolt and the bottom bolt, then loosen the long adjusting bolt while pushing down on the alternator. Remove the belt.
Unplug wire from top of alternator.
Unbolt the wire from the rear of alternator. Completely remove upper and lower bolt from the alternator. Pry the alt away from the brackets. You may have to use a hammer to tap the spacer back in its hole about 1/4 inch. This is located in the hole where the large bolt went through. Reverse procedure to install.

first thing to do is DISCONNECT the battery then remove the wires from the back/bottom ao alternator , undo the top adjusting bolt/nut undo and remove the bottom bolt(s) that the alternater pivots on remove the top bolt completely the alternator is then free replacement is just reverse

12mm 175 thread will do the trick

can you take a pic? might be torx or hex cap.

Take it to advanced auto they will look at it and tell you what you need

free off the alternator bolts then wedge the alternator out to tighten.
then do up bolts.

By the "top pulley" you would be referring to the water pump pulley? This is held on with 4, 10mm head bolts. Make sure you have disconnected the battery and then removed the battery cable from the back of the alternator before continuing.

Yes, very easy...here is the steps to do it:

To Remove:

1. Disconnect battery negative cable.
2. Remove air cleaner inlet pipe.
3. Disconnect alternator electrical connections.
4. Loosen (but do not remove) pivot bolt and tensioner mounting bolt.
5. Remove drive belt form alternator pulley.
6. Remove tensioner mounting bolt and belt tensioner.
7. Remove pivot bolt, loosen adjusting bracket bolt and rotate bracket up.
8. Remove alternator.

To Install:

1. Place alternator on engine.
2. Install (but do not tighten) pivot bolt.
3. Rotate bracket down on top of alternator.
4. Install belt tensioner and install bolt loosely.
5. Install drive belt on alternator pulley.
6. Tighten tensioner bolt to 14-19 ft lb (19-26 Nm).
7. Tighten pivot bolt and bracket bolt to 28-38 ft lb (38-51 Nm).
8. Connect alternator electrical connections.
9. Install air cleaner inlet pipe.
10. Connect battery negative cable.

1. Remove or disconnect the following:
2. Negative battery cable

• Front air intake inlet pipe bolts
• Top hose from the air intake inlet pipe
• Air intake inlet pipe clamp and the pipe
• Alternator B terminal cover cap
• Alternator B terminal nut and the B terminal lead
• Alternator L and S electrical connections
• Alternator pivot bolt and the tensioner mounting bolt, loosen but do not remove
• Drive belt(s); relieve tension on the belt by rotating the adjustment bolt
• Alternator tensioner mounting bolt and the belt tensioner
• Alternator pivot bolt

1. Loosen the bolt at the base of the adjusting bracket and rotate the bracket up.
2. Remove or disconnect the following:
   • Alternator