1978 911 Marchall alternator bearing replacement
09-10-2011, 02:19 AM
#1
1978 911 Marchall alternator bearing replacement
I searched here and over on pelicanparts and did not find a completely detailed documentary DIY post of alternator bearing replacement. Plenty of posts saying, "I just replaced the bearings in my alternator, and it's so much smoother now..." but how'd you do it, man. And, I mean really, exactly how did you do it. No one wanted to say exactly how they did it. So, here's my attempt to provide a very detailed DIY on this topic. My 911 is a 1978 911SC with the Marchall alternator. Any other alternators are going to be fairly similar, but there will be some design differences.
Removing the alternator from the engine is detailed in any number of places, most notably 101 Projects for you 911. This DIY post starts where you have the alternator on your bench. By no means am I saying this is how you have to do this job. There is often more than one way to skin a cat, but this is how I did it with lots of gory details included.
The first thing is to remove the fan from the shaft. Some say that it came off pretty easy for them. Recently, one Rennlist member said he simply dropped the alternator shaft-down onto some shop rags on a hard surface (to protect the threads of the shaft), and the fan just slid off. I bought a press specifically for this bearing replacement job with the expectation that I would have a lot more use for it in the future, and doing this job on my own, rather than paying a rebuilder, pretty much paid for the press already. I used the press to remove the fan. Any job is much easier with the right tools. So, I positioned the fan on blocks of wood as shown in the pic below and pressed the shaft of the alternator off the fan. The fan goes around the circumference of the alternator, so it's easy to support just the fan while the alternator gets pushed down by the press. If you don't have a press, the alternative is a rubber or plastic mallet or hammer with a block of wood used to protect the shaft as you're pounding it down off the fan. When the fan is off, be sure to retrieve the Woodruff key and keep it in a safe place.
Another alternative, which I thought was pretty ingenious, was posted on pelicanparts. One guy threaded coat hanger through the holes on the fan and was able to use a standard puller to pull the fan off.
http://forums.pelicanparts.com/porsc...n-removal.html
Others mentioned tapping the holes on the fan and using one of the special pullers that threads into holes on the object being pulled. Do whatever you have the tools to do.
When the fan is off, there is a cone shaped washer between it and the bearing. Note the orientation, narrow side facing the bearing. There is another cone washer behind the bearing, too.
This is a good time to remove the brush assembly (or voltage regulator plus brush assembly if you have an internal voltage regulator). It's just two screws. Inspect the brushes, and make a call whether to replace the brushes (or voltage regulator if it's an internal regulator alternator).
Remove the 6 long hex cap screws around the circumference of the alternator.
The top and bottom case halves can rotate free of one another at this time, which is good because to press the front case half (and front bearing) off the shaft, it helps to be able to rotate the bottom half a bit to allow you to better support the front case half while pressing out the shaft. So, position the front case half on blocks of wood (You can just catch the bolt "ears" on the edge of the wood blocks.) I used the metal arbor plates that came with the press (the black blocks in the pic). They give a more solid support than just wood alone. Good to have in this case when you can just barely get the bolt "ears" of the case half on the support to begin with. Get everything set and press away. (In the pic below, the 6 hex cap screws are still installed. These screws should be removed by now. I forgot to take a pic when I was disassembling the alternator, so this pic was taken during reassambly, and then, I forgot to take the pic before putting the screws back in. My bad)
My bearing was frozen to the shaft a bit. There was quite a "snap" sound when the bearing broke loose. And, note that I pressed directly on the threaded end of the shaft. If pounding the shaft off with hammer or mallet, you should protect the threads with a block of wood on the tip of the shaft. I probably should have put wood between the press and the shaft myself.
There will be another cone washer behind the front bearing. Note the orientation, narrow side toward the bearing. Remove it and save it.
With the front case half off the shaft, you'll see the front bearing retained in the case half by a plate held by three screws. Remove the three screws. They may be stiff from corrosion and threadlocker. And, then remove the bearing retainer plate.
Press or use a drift to hammer the front bearing out of the front case half. No need to be careful with the bearing here as you'll be replacing it. You'll now have the front case half, old front bearing, front bearing retainer and screws, and the shaft and rotor still stuck in the rear case half. In the lower right of this pic, you'll also see the conical washers.
Removing the alternator from the engine is detailed in any number of places, most notably 101 Projects for you 911. This DIY post starts where you have the alternator on your bench. By no means am I saying this is how you have to do this job. There is often more than one way to skin a cat, but this is how I did it with lots of gory details included.
The first thing is to remove the fan from the shaft. Some say that it came off pretty easy for them. Recently, one Rennlist member said he simply dropped the alternator shaft-down onto some shop rags on a hard surface (to protect the threads of the shaft), and the fan just slid off. I bought a press specifically for this bearing replacement job with the expectation that I would have a lot more use for it in the future, and doing this job on my own, rather than paying a rebuilder, pretty much paid for the press already. I used the press to remove the fan. Any job is much easier with the right tools. So, I positioned the fan on blocks of wood as shown in the pic below and pressed the shaft of the alternator off the fan. The fan goes around the circumference of the alternator, so it's easy to support just the fan while the alternator gets pushed down by the press. If you don't have a press, the alternative is a rubber or plastic mallet or hammer with a block of wood used to protect the shaft as you're pounding it down off the fan. When the fan is off, be sure to retrieve the Woodruff key and keep it in a safe place.
Another alternative, which I thought was pretty ingenious, was posted on pelicanparts. One guy threaded coat hanger through the holes on the fan and was able to use a standard puller to pull the fan off.
http://forums.pelicanparts.com/porsc...n-removal.html
Others mentioned tapping the holes on the fan and using one of the special pullers that threads into holes on the object being pulled. Do whatever you have the tools to do.
When the fan is off, there is a cone shaped washer between it and the bearing. Note the orientation, narrow side facing the bearing. There is another cone washer behind the bearing, too.
This is a good time to remove the brush assembly (or voltage regulator plus brush assembly if you have an internal voltage regulator). It's just two screws. Inspect the brushes, and make a call whether to replace the brushes (or voltage regulator if it's an internal regulator alternator).
Remove the 6 long hex cap screws around the circumference of the alternator.
The top and bottom case halves can rotate free of one another at this time, which is good because to press the front case half (and front bearing) off the shaft, it helps to be able to rotate the bottom half a bit to allow you to better support the front case half while pressing out the shaft. So, position the front case half on blocks of wood (You can just catch the bolt "ears" on the edge of the wood blocks.) I used the metal arbor plates that came with the press (the black blocks in the pic). They give a more solid support than just wood alone. Good to have in this case when you can just barely get the bolt "ears" of the case half on the support to begin with. Get everything set and press away. (In the pic below, the 6 hex cap screws are still installed. These screws should be removed by now. I forgot to take a pic when I was disassembling the alternator, so this pic was taken during reassambly, and then, I forgot to take the pic before putting the screws back in. My bad)
My bearing was frozen to the shaft a bit. There was quite a "snap" sound when the bearing broke loose. And, note that I pressed directly on the threaded end of the shaft. If pounding the shaft off with hammer or mallet, you should protect the threads with a block of wood on the tip of the shaft. I probably should have put wood between the press and the shaft myself.
There will be another cone washer behind the front bearing. Note the orientation, narrow side toward the bearing. Remove it and save it.
With the front case half off the shaft, you'll see the front bearing retained in the case half by a plate held by three screws. Remove the three screws. They may be stiff from corrosion and threadlocker. And, then remove the bearing retainer plate.
Press or use a drift to hammer the front bearing out of the front case half. No need to be careful with the bearing here as you'll be replacing it. You'll now have the front case half, old front bearing, front bearing retainer and screws, and the shaft and rotor still stuck in the rear case half. In the lower right of this pic, you'll also see the conical washers.
Last edited by Brett San Diego; 09-14-2011 at 04:59 PM.
09-10-2011, 02:58 AM
#2
continuing
The rotor shaft is held in the rear case solely by a plastic bearing cup. This cup may be damaged as mine was.
The rear bearing cup
How mine is broken. My bearing cup has some spiral splits in the plastic between the bearing and the case.
I deemed it still serviceable, however. Where it is split is the plastic that takes up the clearance between the bearing and case. No plastic is missing; it's just split, and there is little movement expected here, so I think things will stay in place fine. I don't know where to get a replacement anyway. Maybe an alternator shop has something. An old thread on Pelicanparts said to call one of the pelican employees to get one. I have no idea if that is still possible. Another guy on the pelicanparts forum made his own:
http://forums.pelicanparts.com/porsc...placement.html
His was damaged more than mine. I contacted the OP of that thread on the off chance that maybe he made a few copies, but no luck.
Next is to get the rotor out of the rear case half, so you can access the rear bearing. The rotor is held in the rear case half only by the plastic bearing cup. You may be able to just hold the case and pull the rotor out. I couldn't, but I didn't know how hard it was safe to pull. (At the time I wasn't sure exactly what was holding the rotor in.) So, I put the case between blocks of wood and pulled up on the shaft while standing on the wood. If you have a vise big enough, you could put the case in a vise. Don't squeeze it too tight.
Now, you'll need to pull the rear bearing, but the clearance behind the bearing is too tight to fit the claws of a typical puller.
I went to Harbor Freight and bought one of these bearing splitter/puller kits, which worked perfectly.
Position the splitter wedge behind the bearing and set it up with the screw puller and pull the bearing off.
The rear bearing cup
How mine is broken. My bearing cup has some spiral splits in the plastic between the bearing and the case.
I deemed it still serviceable, however. Where it is split is the plastic that takes up the clearance between the bearing and case. No plastic is missing; it's just split, and there is little movement expected here, so I think things will stay in place fine. I don't know where to get a replacement anyway. Maybe an alternator shop has something. An old thread on Pelicanparts said to call one of the pelican employees to get one. I have no idea if that is still possible. Another guy on the pelicanparts forum made his own:
http://forums.pelicanparts.com/porsc...placement.html
His was damaged more than mine. I contacted the OP of that thread on the off chance that maybe he made a few copies, but no luck.
Next is to get the rotor out of the rear case half, so you can access the rear bearing. The rotor is held in the rear case half only by the plastic bearing cup. You may be able to just hold the case and pull the rotor out. I couldn't, but I didn't know how hard it was safe to pull. (At the time I wasn't sure exactly what was holding the rotor in.) So, I put the case between blocks of wood and pulled up on the shaft while standing on the wood. If you have a vise big enough, you could put the case in a vise. Don't squeeze it too tight.
Now, you'll need to pull the rear bearing, but the clearance behind the bearing is too tight to fit the claws of a typical puller.
I went to Harbor Freight and bought one of these bearing splitter/puller kits, which worked perfectly.
Position the splitter wedge behind the bearing and set it up with the screw puller and pull the bearing off.
Last edited by Brett San Diego; 09-11-2011 at 08:50 PM.
09-10-2011, 03:29 AM
#3
and continuing
Time to reassemble with new bearings. Here are the bearings needed.
The bearings that came out of my alternator were Nachi brand. Front was a 6303 NSL; rear was a 6200 NSL. I decided to replace with the identical Nachi bearings. These are standard size 2 rubber seal bearings. (Other manufacturers call them 6303 2RS or 6200 2RS for 2 Rubber Seals, but I guess Nachi has its own naming thing going on.) I had difficulty finding a Nachi 6303 NSL bearing until I finally found some on Ebay. I kept seeing NSE bearings, but I wasn't sure if they were the same thing as NSL. It wasn't until after I ordered the Ebay bearing that I came across some Nachi literature that stated that the NSE bearings are a new design that replaces the NSL bearings. At that point I ordered the 6200 NSE for the rear.
OK, clean up the front case and get it ready for the front bearing. I went over the bearing mating surface with 1500 grit emory paper. Then, I used the press with a drift to press the bearing in the case, making sure it was squarely seated all the way in. Again, if you don't have a press, you can use a hammer or mallet and blocks of wood.
Bearing and case in position.
Drift in position on top of bearing. You want to use a bearing drift (or block of wood) that will press on the outer race of the bearing. Don't press just on the inner race.
Bearing pressed in.
And, screw the bearing retainer back into place. I put a little threadlocker on the screws, since they had some when I took it apart.
The bearings that came out of my alternator were Nachi brand. Front was a 6303 NSL; rear was a 6200 NSL. I decided to replace with the identical Nachi bearings. These are standard size 2 rubber seal bearings. (Other manufacturers call them 6303 2RS or 6200 2RS for 2 Rubber Seals, but I guess Nachi has its own naming thing going on.) I had difficulty finding a Nachi 6303 NSL bearing until I finally found some on Ebay. I kept seeing NSE bearings, but I wasn't sure if they were the same thing as NSL. It wasn't until after I ordered the Ebay bearing that I came across some Nachi literature that stated that the NSE bearings are a new design that replaces the NSL bearings. At that point I ordered the 6200 NSE for the rear.
OK, clean up the front case and get it ready for the front bearing. I went over the bearing mating surface with 1500 grit emory paper. Then, I used the press with a drift to press the bearing in the case, making sure it was squarely seated all the way in. Again, if you don't have a press, you can use a hammer or mallet and blocks of wood.
Bearing and case in position.
Drift in position on top of bearing. You want to use a bearing drift (or block of wood) that will press on the outer race of the bearing. Don't press just on the inner race.
Bearing pressed in.
And, screw the bearing retainer back into place. I put a little threadlocker on the screws, since they had some when I took it apart.
09-10-2011, 04:04 AM
#4
Still going
The front bearing needs to go on the shaft before putting the rotor back in the rear case half. You'll remember that the only thing holding the rear of the rotor is the plastic bearing cup. You can't press (or pound) the front bearing on the shaft if the plastic cup is all that is holding the shaft. You'll just push the rotor out of the back side of the case destroying the plastic cup.
I first went over the front and rear of the shaft with 1500 grit emory paper.
Put the cone washer that goes behind the front bearing on the shaft (narrow side to the bearing), and press or drive the front bearing with the front case half onto the shaft. This time you want to press only on the inner race so as not to damage the bearing. I used a 19 mm deep well socket as a drift. It had the right diameter to hit the inner race.
Turn the shaft over and press on the rear bearing, again pressing only on the inner race. I used an appropriately sized socket again.
Now, mate the rotor/front case assembly with the rear case half. The rear bearing needs to get pushed into the rear bearing cup. Support the backside of the rear bearing cup when pushing the rear bearing into the cup. You don't want to damage the bearing cup if it isn't already damaged, or you don't want to push the bearing cup out of place if it already is split like mine was. I could push things together by hand here.
Lastly, install the 6 allen cap screws around the perimeter. Orientation is not important. The front of the case is symmetrical. Bearing replacement is done.
Do not try to press the fan on the front of the shaft at this time. You will just push the shaft out of the backside of the case and damage the rear bearing cup. First, re-install the alternator in the fan housing, secure the housing back on the engine, then use the alternator pulley nut to push the fan on the shaft as you install the pulley. Don't forget the cone washer between the front bearing and the fan (narrow side to the bearing) and the Woodruff key for the fan.
I hope this is found to be helpful.
cheers,
Brett
I first went over the front and rear of the shaft with 1500 grit emory paper.
Put the cone washer that goes behind the front bearing on the shaft (narrow side to the bearing), and press or drive the front bearing with the front case half onto the shaft. This time you want to press only on the inner race so as not to damage the bearing. I used a 19 mm deep well socket as a drift. It had the right diameter to hit the inner race.
Turn the shaft over and press on the rear bearing, again pressing only on the inner race. I used an appropriately sized socket again.
Now, mate the rotor/front case assembly with the rear case half. The rear bearing needs to get pushed into the rear bearing cup. Support the backside of the rear bearing cup when pushing the rear bearing into the cup. You don't want to damage the bearing cup if it isn't already damaged, or you don't want to push the bearing cup out of place if it already is split like mine was. I could push things together by hand here.
Lastly, install the 6 allen cap screws around the perimeter. Orientation is not important. The front of the case is symmetrical. Bearing replacement is done.
Do not try to press the fan on the front of the shaft at this time. You will just push the shaft out of the backside of the case and damage the rear bearing cup. First, re-install the alternator in the fan housing, secure the housing back on the engine, then use the alternator pulley nut to push the fan on the shaft as you install the pulley. Don't forget the cone washer between the front bearing and the fan (narrow side to the bearing) and the Woodruff key for the fan.
I hope this is found to be helpful.
cheers,
Brett
Last edited by Brett San Diego; 09-11-2011 at 08:54 PM.
03-04-2015, 07:35 PM
#5
Instructor
Excellent DIY, thank you. I am just doing mine, but when I pulled my alternator apart, the front bearing was 6203, not 6303, so my ordered parts were incorrect. No big deal, just a couple of days delay.
