Alternator Replacement on a 528
This is a DIY for an alternator swap on a 528 (M52) I6 engine. Mine is a 1998 with a build date of 12/98 and has a Bosch 120 amp alternator. Total time was about 4 hours the first time, 1.5 the second. (Ive owned a few bimmers)
- Disconnect the battery. You will be taking off the positive lead from the alternator. If it touches anything there will be sparks.
- The air box has to go first. Its held in by one 10mm bolt and several tubes for the air, and two electrical connections. I removed the MAF separately. It takes a lot of wiggling and twisting to get the air box out, but it will give in eventually. Taking the MAF out gives a little more flexibility.
- Once that’s out of the way you have a clear view of the offending part. Note the brand of the alternator. Its either a Bosch or Veleo (sp?). Order the correct one to replace it. I think the cases may be slightly different and may not match up with the air vent.
--Disconnect the alternator positive lead and unclip the other wire harness. Push the spring clip Down to release.
- Remove fan shroud and fan. I didn’t want to do this, but there was no way I could have fit my hands down to get to the belt tensioner without removal of the shroud and fan. It turned out to be pretty easy.
-- Remove the fan by turning the reverse thread nut and holding the pulley. Mine wasn’t very tight. There is a thread on how to make a pulley holding tool, see the last photo (compliments of BimmerBoard.com), or you can try using a LARGE screwdriver between the pulley screw heads. I made the tool. Cost $11 at Home Depot for the metal.
-- Remove the shroud. Pull the two plastic rivets at the top corners of the shroud. Start working the piece up. It takes a little work getting it around the radiator hoses and stuff. There is a small ½” hose that runs along the top of the radiator to the overflow bottle. It will need to be disconnected and plugged, since I had quite a bit of anti-freeze wanting to come out. I taped it off with self sealing silicone tape. There is a large hose that runs along the bottom and can easily be left connected. Set aside.
- Now you have a huge amount of space to get to the alternator.
-Remove the belts. This is a good time to replace them unless you did it within the last 6 months.
-Replace the idler pulleys. The single pulleys for the 2 tensioners are about $15 each. The off set pulley for the Alternator is about $25. I would rather do it now than opening it up again later. They come off with a 16 mm socket and an 8mm allen for the AC tensioner. They should turn freely and have no play at all. Inspect the water pump pulley. Its plastic, but no bearings. Replace if needed.
--The A/C belt hyd tensioner is moved with a 8mm allen. It takes a lot of leverage to move it, so plan on a ratchet or bar, not the L-shape keys
--The Alt/Hyd/water pump belt tensioner is turned with a 16mm socket.
- Once the belts are off, take off the two 16mm bolts holding the alternator on. They are easy to get to once everything is out of the way. The lower bracket holding the alt on to the block was tight on mine. I had to pry the alternator off, even with the bolts removed. Also, note the alignment tab on the idler pulley when you put it back on.
-Issues with reinstallation
--Like I said before the alternator lower bracket was tight. It made it a pain to line up the lower bolt.
--Fan shroud fought going back in. Have a beer handy. And don’t forget to have the fan go down WITH the shroud. There are tabs on the lower end of the shroud that keep it in place down below. Make sure it is held in place on the lower end.
--Clean out the alternator cooling hose. Mine was stuffed with leaves.
- This is an easy job and can be done in 1.5 hours if your in a hurry. It just takes some digging to get to the actual Alternator.
Last edited by Flybot; 09-25-2009 at 03:54 PM.
There has been alot of demand for an I6 DIY.
Just curious how many miles when your Alternator failed?
About 141K miles. The idler pulleys were pretty loose as well.
Off to the DIY section.
New to this site so hello!
I've got an E39 2001 525i and have followed the instructions for removing my alternator.
I loosened the 8mm hex bolt on the tensioner which was already loose. I think I got the belt off with more luck than anything.
What is the best way to put the belt back on? The tensioner os obviously spring loaded but how do I go about holding it back to slip the belt back on??
2001 E39 525i
Not sure if it is the same on the I6 but on my V8, if you look very closely at the 8mm tensioner nut, you will notice ANOTHER hex "nut" which is part of the bracket underneath.
First you'll need to mount the bracket with the belt placed loosely on the pulley
Then, while using another wrench to turn that bracket nut clockwise to take up the belt slack. You will see the bracket move up and the belt tighten up.
Finally, tighten the 8mm to 30 ft/lbs and double check the belt is taught.
I further add to this excellent DIY, I wrote a DIY that also includes Alternator Removal Info here:
DIY: 1998 528I Oil Filter Housing Gasket & "Freeze Plugs" Repair:
Just did mine 2 nite, in the dark outside, in the cold down to 10 degrees towards the end. I managed to do it without taking the fan or shroud off. I have various types and lengths of extensions and deep well sockets and short and long arm ratchet wrenches that allowed me to bypass any fan removal. But now I found that I should have bought 2 idlers as they are both loose. Took about 3 hours. Also I found the Ultima alternator from Oriellys had a compression nut on the bottom mount so there was plenty of clearance when setting the alternator in place and just make sure the bolt sucks the nut in when you tighten it, mine made a ball joint popping sound when it sucked in..