Alternator swap 55A to 70A, single piece pulley v split pulley - Mercedes-Benz Forum
 
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post #1 of 9 (permalink) Old 06-08-2019, 01:57 PM Thread Starter
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Alternator swap 55A to 70A, single piece pulley v split pulley

Hi,

I thought this was going to be one of the simple jobs...

I'm replacing the (working) 50 Amp Bosch AL80X alternator with the 70 Amp AL68X Alternator on my '76 450SL. The original had a slight bearing noise, and I thought I might as well replace it and get some more Amps into the bargain...

Because shiny things are nice (!) I also decided to fit a new pulley and fan at the same time.

The pulley I bought is a single piece pulley - but has no keyway for a woodruff key. However, it did come with a large flange nut and split washer (note that the photos of this 6033GD5100 online show a large flat washer with key way, instead of the split washer mine included). The pulley is listed as being compatible with the AL68X alternator, and the 450SL.

The original alternator has a pulley that splits into two halves, front and back, with a keyway for a woodruff key.

The new 70A alternator does include a woodruff key, but there's no way to use it, because the single piece pulley doesn't have a slot, so you couldn't put it on the shaft with the key in place.

So...I decided that presumably one wasn't needed. I've fitted the new fan, pulley, split washer and nut onto the new alternator. I used the air gun. All I can hold is the fan or pulley while tightening (I see some reference elsewhere to some bosch alternators having hex sockets on the end so you can hold them, but nothing on this one..

What I've discovered is that with that arrangement, the fan is not held that tight, even when the nut is tight on the shaft. I can spin the fan on the shaft, if I hold the nut, though not easily.

The pulley will also slip, if I try and turn it anti-clockwise, again while holding the nut (when running, the motor will turn it clockwise). It doesn't seem to slip going clockwise, presumably because of the spring washer digging into it slightly.

If I spin the pulley or fan by hand, without trying to hold the nut, nothing slips, and the alternator spins freely. My concern is that there will be more torque when the motor is running, and the alternator is generating current, and the pulley will spin on the shaft (my guess is that there is very little torque on the fan, so that won't be an issue).

Does anyone know if this is normal? I have found other other threads indicating that some bosch pulleys don't need a woodruff key, as the turning of the motor will naturally tighten everything).

I could, of course, fit my old (rusty) split rim pulley (and the woodruff key) to the new alternator, but I prefer the shiny one!

Also....a quick Google search and the EPC didn't show the two piece split pulley - I was considering buying one of those, so I could use the woodruff key. Anyone know the part number (s)?

-Steve


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post #2 of 9 (permalink) Old 06-08-2019, 05:43 PM
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I remember of some pulleys (unrelated to cars) being conical in the spindle and that could be the ones without the woodruff key. These use bolt at the front to make excessive interference as the bolt pushes the cones together.
At max power the alternator will provide substantial resistance to the pulley and I cannot think anything less than woodruff will do (or whatever factory designed for the used alternator).

OTOH, if the total load to the alternator never exceeds 50 amps, the difference to 70A would be only the space alternator occupies. Sure, there are benefits, mostly not commensurating with the effort and cost involved.

.
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post #3 of 9 (permalink) Old 06-24-2019, 06:24 PM Thread Starter
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Having solved this problem, thought I'd share the findings with others just in case they encounter the same issue.

If your alternator has a 'split' pulley with woodruff key, the replacement part number is Bosch 126600382. This seems to be a lot harder to find than the solid pulleys listed all over the place.

This includes the two halves of the pulley, spacers that go either side and a nut and split washer.

I also bought a new fan (separately). The photo below shows all the parts, and the order they go on the shaft. Note that my new fan looks slightly different than the original, but seems to fit fine.

The new metal disk on the left seems to be for some fitment that requires the fan to be spaced away from the body of the alternator. Didn't seem to be needed on my car. Also note that in the photo I've shown a flanged nut that came with the single piece pulley. I actually used the regular nut that came with the split pulley, just as per the old one.
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post #4 of 9 (permalink) Old 06-25-2019, 12:29 PM
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Great find, how much more work do you have left on your Car?


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post #5 of 9 (permalink) Old 06-25-2019, 04:44 PM Thread Starter
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Originally Posted by RaceDiagnostics View Post
Great find, how much more work do you have left on your Car?
Too much!!

Seriously....

Front suspension is all in pieces, but has new ball joints, bushes etc fitted and is painted. The alternator was the last of the engine accessories to finish - everything is now in boxes awaiting re-installation.

Now I've got to replace some hoses and lines under the hood, reinstall all the accessories, install the subframe and steering,brakes, radiator, condenser etc and hopefully that's the mechanical stuff done (it was running only a month ago). Then the interior goes in (though that should be relatively simple - seats and carpets are all in storage awaiting installation). Windshield, wheels and tires and and hopefully I can register the car. Once it's on the road I'm sure there will be some bugs to work out.

How long? If it's finished before next summer, I'll be happy....but it all depends on work and how that intrudes. My wife is already planning trips she will be taking in it...

How is yours going?

(Photos below taken last month before I pulled the subframe and pulled all the accesories off the motor.
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post #6 of 9 (permalink) Old 06-26-2019, 12:51 AM
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I'm almost ready to go for an mot

Last week I put the new exhaust on.....

https://www.racediagnostics.com/gall...i-state=dialog

....then the wheel arch liners.

https://www.racediagnostics.com/gall...i-state=dialog

Just the bonnet to go back on when I return from holiday this week. Still a few bits and bobs to finish off though but will finish these off in time.
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post #7 of 9 (permalink) Old 06-26-2019, 03:23 PM Thread Starter
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Originally Posted by RaceDiagnostics View Post
I'm almost ready to go for an mot

Last week I put the new exhaust on.....

https://www.racediagnostics.com/gall...i-state=dialog

....then the wheel arch liners.

https://www.racediagnostics.com/gall...i-state=dialog

Just the bonnet to go back on when I return from holiday this week. Still a few bits and bobs to finish off though but will finish these off in time.
Wow!!! That is impressive....incredible job - especially the photos under the rear axle.


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post #8 of 9 (permalink) Old 06-27-2019, 08:44 PM Thread Starter
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[QUOTE=RaceDiagnostics;17824722]I'm almost ready to go for an mot


....then the wheel arch liners.

https://www.racediagnostics.com/gall...i-state=dialog

How did you attach the wheel arch liners? I bought some 'buttons' that were on shown on the EPC as the retainers for the liners (my 450SL didn't have them originally), but it's not clear how to use them - it looks like there should be a threaded stud attached to the car for each plastic button to thread onto.

-Steve


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post #9 of 9 (permalink) Old 06-28-2019, 08:29 AM
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I did a trial fit and marked up the fixing positions.



I then put in riv-nuts and welded in studs.



Epoxy primer next...



...then ruberised stone chip....



....and finally 2k top coat.



...and then repeat on the other side. So glad that is all behind me now.


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