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  #1  
Old 06-04-2010, 08:07 PM
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Replacing 240D accessory drive belts

Hi, thought I would share what I learned and maybe learn a little more in return... today's job (and sadly, it took more of today than I would have liked ) was replacing accessory drive belts on my 240D. I had tried last weekend to get going on a valve adjustment, but the belts were so loose that they slipped when I tried to rotate the engine by putting a wrench on either the steering pump or the alternator. I guess I have better compression than I thought. The belts were kind of squeaky anyway, and the alternator was all the way to the end of its adjustment, so I figured it was time to replace the whole set.

Anyway, what I learned was that

1. The factory service manual is kind of skimpy on this. I skimmed it, didn't see anything too tricky, refers to special tension measurement tools I don't have, etc.

2. My power steering pump has a tensioning bolt that isn't shown in the manual (see photo with red arrow to tensioning bolt). Basically, when you tighten that bolt it pulls the power steering pump up, increasing tension; there's a specially shaped nut with a hook that goes into the body of the pump, and it pulls as you tighten.

3. For the life of me I couldn't figure out how to loosen the tension on the belt that drives the air conditioning compressor. To my eyes it looks like the whole darn thing is non-adjustable, but I must be missing something. On this style of AC compressor system do you have to remove the whole pump to get the belt on and off?? I ended up just cutting the old belt off, since my pre-purchase inspection had revealed it to be low on refrigerant and non-operational anyway. I'm including a photo of the top and bottom of the AC compressor in case anyone wants to point out what I'm missing in the way of an adjustment method. There's a scan of the manual below, but I couldn't match up what I've got to what it shows.

4. Since I don't have the fancy measurement tools, does anyone have a recommendation for how much deflection for how much pounds pushing on a belt?

When I get back to doing the valve adjustment, does it make sense to pull all the glow plugs so that the engine is easy to turn over? Are there one-time-use gaskets that need to be replaced if I do that? Seems to me I recall reading something about that.

Cheers, thanks for your help.

Kurt

Attached Thumbnails
Replacing 240D accessory drive belts-fsm_refrigerantcompressorbelt.jpg   Replacing 240D accessory drive belts-p0709_mercedessteeringpump.jpg   Replacing 240D accessory drive belts-p0714_mercedesaccompressor.jpg   Replacing 240D accessory drive belts-p0716_mercedesunderac.jpg  
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Old 06-04-2010, 10:45 PM
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Can't tell from your pic but...loosen the bolts that hold the compressor to the engine. Then turn the threaded adjuster marked in read counter clockwise to loosen the compressor. The compressor will either pivot or slide down its adjustment slots.

I use a belt 1/2" shorter than stock on the SD and have to rotate the engine to get some of the belt on but it is correctly adjusted near the middle of compressor travel. Use your finger to deflect belt 1/2" or so in lieu of the fancy gauge. You don't want it too tight or you'll damage bearings.

Don't pull the glow plugs. Use a 1.2" ratchet with proper size socket (27mm on SD) with a short say 1.5" extension on the center nut on the crank shaft. Turn in direction of normally running engine.
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Old 06-05-2010, 01:34 AM
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and facing the motor, is the correct direction clockwise or counter clockwise ?
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Old 06-05-2010, 10:17 AM
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Quote:
Originally Posted by TnBob View Post
and facing the motor, is the correct direction clockwise or counter clockwise ?
Clockwise.
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Old 06-05-2010, 10:28 AM
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That is the older style A/C and my manual says the same thing. I haven't seen one of those, so can't comment.
Measure the deflection in the middle of the belt, you're looking for a half an inch and an inch.
The power steering is adjusted by that bolt, loosen the three bolts holding it on and then turn the bolt.
I wouldn't remove the glow plugs unless you're going to change them out, as mentioned, use a 27mm or 1 1/16 inch socket on the crank.
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Old 06-05-2010, 12:53 PM
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Glowplugs

I'm curious why you would recommend against pulling the glow plugs? Is it just that it's one more possible thing to screw up ? I actually did have an ulterior motive for pulling them: I was planning to do the Marvel Mystery Oil soak in the cylinders. I've been running for a week with MMO in the crankcase, and darned if it doesn't seem to run smoother and more powerfully. That troublesome low compression cylinder may be coming around after all.

Kurt
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Old 06-05-2010, 01:03 PM
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It's been a long time since I replaced the AC belt on my 77 300d which had that style of compressor. My recollection is that the idler pulley adjusted on it. I may be completely mistaken.
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Old 06-05-2010, 01:28 PM
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Hey Kerry

On the 77 300D, if I switched to the r4 compressor from the york, are the expansion valves going to stay the same??
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Old 06-05-2010, 02:00 PM
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Quote:
Originally Posted by Argospete View Post
Hey Kerry

On the 77 300D, if I switched to the r4 compressor from the york, are the expansion valves going to stay the same??
No idea. I'm an idiot when it comes to AC.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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Old 06-05-2010, 02:52 PM
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Quote:
Originally Posted by gastropodus View Post
I'm curious why you would recommend against pulling the glow plugs? Is it just that it's one more possible thing to screw up ? I actually did have an ulterior motive for pulling them: I was planning to do the Marvel Mystery Oil soak in the cylinders. I've been running for a week with MMO in the crankcase, and darned if it doesn't seem to run smoother and more powerfully. That troublesome low compression cylinder may be coming around after all.

Kurt
The only reason not to, is there's no reason to pull 'em.
But if you want to do a MMO soak, go ahead and yes, there is a one time use heat shield in the hole, replace them and install dish side up.
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Old 06-05-2010, 03:19 PM
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Quote:
Originally Posted by toomany MBZ View Post
The only reason not to, is there's no reason to pull 'em.
But if you want to do a MMO soak, go ahead and yes, there is a one time use heat shield in the hole, replace them and install dish side up.
I believe you are thinking of the injectors, not the glowplugs.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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Old 06-05-2010, 03:32 PM
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^ Doh! You're right, there aren't any washers or anything else in the glow plug holes.
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Old 06-05-2010, 05:24 PM
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From what I remember from the last time I changed those belts there is a section in the manual that describes how you would measure the belt tension without a gates device. The long sections of belt should deflect around 1/2" and the short sections should only deflect about 1/4". They give specific lengths, but I'm pretty sure this method should work just fine. They also tell you to tighten the tensioner on the alternator a small bit after you have tightened all of the other bolts. This keeps tension on the bolt, holding it in place. Other people have said they have to continuously tighten the alternator belt, but this hasn't been the case so far.

My ac compressor was in a different place or I'd give you some advice. I think I had to use a piece of softwood to brace and push against the compressor to get the belt on though.
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Old 06-05-2010, 07:30 PM
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That smaller pulley to the right is the idler pulley (referring to the third picture). Feel behind and you should find a bolt. Loosening the bolt will allow the pulley to rotate counterclockwise, relieving tension on the belt. Use another wrench on the bolt on the front of the pulley to tension the belt and then tighten the rearward bolt.
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Last edited by yellowbenz; 06-05-2010 at 07:56 PM. Reason: clarify
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Old 06-05-2010, 07:55 PM
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Well, I looked at ALL of the photos finally. Photo one highlights what I talked about above. It is a pic of the idler pulley to the right of the York compressor (if you are facing the car). Procedure as described in the photo.

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