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Old 07-10-2003, 10:58 AM
Registered User
Join Date: Jun 2002
Location: Connecticut
Posts: 118
Angry Need help! How to access stripped fan hex nut?

I am in the midst of replacing the serpentine belt tensioner on my 1992 300TE 4Matic wagon, (for the first time). Before I began the job, a mechanic told me the fan hex nut was stripped, which I have confirmed, so I removed the radiator and shroud, to gain access. But having now done so, I realize that due to the air conditioning unit, (looks like a thin radiator with metal tubes running through it?), and two auxillary fans, there still isn't sufficient space to fit a drill in their to remove the stripped bolt. Am I correct in assuming that these items have to be removed, (or pushed aside?), and if so, what is the procedure - can I do it or is that a professional job only? I have no idea what I am doing when it comes to A/C and I can' find anything regarding removal in the 124 repair CD other than job # 83-560 which pertains only to the removal of the auxillary fans. Am I stuck, or do I have any options? What are the dangers, if any, to merely unscrewing the nuts and removing the whole unit? Thanks in advance!

1962 MB 220SEb Sedan
1992 MB 399TE 4Matic Wagon
1995 Subaru Legacy AWD Wagon
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Old 07-10-2003, 11:10 AM
Posts: n/a
Mine was also stripped/seized. The A/C parts were removed by the dealer including the R134 discharge and recharged after the job. It can be a tough job. I bet some one here has done it though. I let my dealer do it.
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Old 07-10-2003, 11:34 AM
DR.DIESEL's Avatar
Senior Member
Join Date: Mar 2003
Location: Puget Sound, Washington St.
Posts: 522
Get a tool from Snap-On or Mac Tools called an EASY-OUT.
They sneak down and grab onto the stripped bolt.
I use them for this job and have never failed.
The Snap-On # is REX10A "Screw Extractor Set"
and really not expensive. $30 I think.
Good luck.
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Old 07-10-2003, 12:16 PM
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Join Date: Jun 2002
Location: Connecticut
Posts: 118
Dr. Diesel, I misspoke in my post: it's actually an allen BOLT, (not a nut), which is stripped. Correct me if I'm wrong, but I thought the only way to get this out is to drill it first, then use an extractor. Is that what the snap-on tool you describe is? I'll certainly look to find it if it works on bolts too! Thanks!
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Old 07-10-2003, 12:46 PM
Posts: n/a
Another idea: if you know a welder - weld another nut on top of the bolt (MIG weld would not be too invasive or generate too much heat) and then simply use the proper size wrench to remove.
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Old 07-10-2003, 01:04 PM
haasman's Avatar
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Join Date: Jun 2001
Location: San Francisco, CA
Posts: 3,097
An EASY-OUT can often work with the head of an allen bolt, depending on the size.

You can also, if room permits, use a chisel and hit the heat perpendicular to the head side in the counter-clockwise direction. Often this will move it enough to get vise grips on it.

Another trick is to fill the allen head with something to take up the slack and ensures the allen wrench holds. It has been suggested to try valve lapping compound which is a gritty paste.

As a rule, I always tap an allen into the allen head to double-check it is fully seated before turning.

Keep us posted,

'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
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Old 07-10-2003, 01:15 PM
bjcsc's Avatar
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Join Date: Nov 2002
Location: Charleston, SC
Posts: 672
Another option, if it isn't countersunk, would be to file two opposite sides of the head flat and take it out with an open end wrench or vice-grips.

Re: Welding: A good way to weld to a cap screw is to sacrafice an allen wrench. Put the wrench in the stripped hole and weld it there. This way you don't have to get "behind" or underneath a nut. It takes less welding, too (brazing works too if the area can take the heat, or if the cap screw doesn't go to ground)

Re: Drilling: Forget it. Most cap screws are hardened and drilling them is a nightmare, unless you can heat them up first.
1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick
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Old 07-10-2003, 03:25 PM
sixto's Avatar
smoke gets in your eyes
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Location: SF Bay Area
Posts: 20,123
JB Weld might be strong enough to bond a nut to the stripped allen head bolt.

95 S420
91 300SE
87 300SDL
83 300SD
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Old 07-10-2003, 04:13 PM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,804
Perhaps you could carve the head away with a dremel tool. The fan would come off, then you could deal with the threaded shank. And perhaps the part behind the fan could come off where you can deal with the problem on the bench.
95 E320 Cabriolet, 140K
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Old 07-10-2003, 06:28 PM
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Join Date: May 2003
Location: Long Island, NY
Posts: 83
Sears has a set of bolt extractors with hardened teeth that grip worn bolts on the outside. They increase their bite as you turn counterclockwise. A set costs about $20.00. You attach them to a socket wrench.
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Old 07-10-2003, 07:02 PM
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Location: Evansville WI
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With damaged allen heads on the fan bolts, I've had good luck tapping a torx bit into the hole. Depending on how chewed up it is, you can use a T45, T47, or T50. The radiator will need to be removed usually to be able to tap it in place, but it beats drilling, as the condensor needs to be removed then.

Just as a side-note though, I hope the original poster and his mechanic realize that the pulley hub does need to be locked into place with a special tool to be able to remove the bolt. If he doesn't realize this, maybe he thinks the THREADS are stripped and not the head?

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Old 07-10-2003, 07:22 PM
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Join Date: Jun 2002
Location: Connecticut
Posts: 118
Gilly, original poster here: I have removed the radiator and have looked at the allen bolt, which as you know is recessed, with a mirror and flashlight. The allen head actually doesn't look completely rounded inside, but when I fit the 8mm allen bit in and move the ratchet counter-clockwise, it does feel like it is slipping past each notch as it's turned. I do not have that special tool you mentioned. Do I really need it? Can't I just hold the fan blade with my free hand, or is there some internal clutch that spins even when the fan blades are still and needs to be held in place? If so, where is the tool inserted and can some makeshift thing be used instead? The mechanic I took the car to was new to me, but they supposedly do a lot of work on MB. Thanks for your and everyone's help and suggestions to get this problem licked!!
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Old 07-10-2003, 07:35 PM
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Location: Evansville WI
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You almost "have" to have a means of locking the fan hub. If you try doing it one more time, you'll notice the pulley behind the fan (the one that turns the fan). When you try turning the bolt, you'll probably notice that the pulley is rotating along with the bolt. Kind of hard to tell. If that pulley is turning, you're not forcing the bolt loose, you're just spinning the pulley (and the hub/bearing that the pulley and fan are bolted to). There are 2 blank holes in the hub (the HUB now, not the pulley; the pulley is bolted to the hub). This special tool is a piece of rod, about 3/16" diameter, with a 90 degree bend at the end. The bent end inserts into either one of these blank holes. The bent end has to be lined up with these 2 "ribs" that are cast into the bearing bracket itself. If you look behind the pulley, slightly to the drivers side (near the crankshaft position sensor) you will see these 2 ribs that the tool "saddles" into.
Typically the way this works is you'd put the tip of the rod into this "saddle" area and then rotate the bolt holding the fan on counter-clockwise. Keep turning until you feel this "tip" go into one of the blank holes. You may get a couple little "ticks" out of the tool as it passes by one of the actual bolt holes, there are 4 bolt holes and 2 blank holes. The 4 bolt holes are the 4 bolts that hold the pulley to the hub. This is the BACK side of the holes though, not the front where the heads are.
You can't really hold it by the fan itself. For one thing it's plastic, for another it's mounted on a viscous clutch, so there is no effort possible on the fan.
The torx sockets really have worked nice for me, but possibly you just aren't actually "turning" the bolt yet.
Good Luck

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Old 07-10-2003, 07:43 PM
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Location: Evansville WI
Posts: 9,616
This is the tool, you may be able to make one OK.
I think I have an old one if you need a good measurement on the rod thickness.
It's the one on the top left:

The "small" 90 degree bend is the end that engages into the hub, the large 90 degree bend would sorta be considered a 'handle". You do need to hold some pressure towards the hub (towards the fan side i guess you could say) while you turn the bolt to get the tip to drop into a blank hole.


ps I just did a search to come up with this picture of the tool, I know nothing about the supplier on this web page, this is not an endorsement. Looks like a decent enough price though.
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Old 07-11-2003, 12:05 AM
Kyle Blackmore's Avatar
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Join Date: Sep 2001
Location: almost beyond Hope...B.C.
Posts: 897
I just went through this on my 300CE , I made the tool to hold the fan and borrowed the proper socket for it. That didn't work so I tried a Torx bit, 50 was too small and 55 was too big. I found a short bolt extractor (5/16") made by Hanson that almost grabbed but not quite . I evacuated the A/C and removed the condenser , along with the rad and aux. fan . I then had room to drill the inside of the bolt about 1/4" deeper with a 5/16" bit and used the bolt extractor to remove the bolt.Simple , no? . I was doing the head gasket at the same time so I had to drain the coolant anyways. The A/C evacuate/recharge was $150 and all the time and scraped knuckles make this a very expensive bolt . If the only reason to remove the bolt is to change the fan tensioner (on a 103), it can be removed without removing the bracket bolt on the front cover completely , just loosen it enough to get the bracket out of the way, then goop some RTV on the bolt before you tighten it to avoid a oil leak there. Good luck
1985 380SE- 160,000km 'Blistu' - Sold
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