Removed the waterpump on my '92 300SE to replace a leaking pump-to-block o-ring. Doing so of course requires releasing the tension on the belt. Also replaced a rattling tensioner shock absorber while I was at it.

Went to reassemble and retension everything and couldn't for the life of me figure out how to set the tension. AllData diagrams indicated I should align the arrow on the tensioner housing with some seemingly non-existent fixed pointer.

I checked another source for info - the CD I got from MB for the car and it has an exploded diagram of the tensioner device that shows a pointer that goes in between the outer bracket and the tensioner body.

The PO said he had recently replaced the tensioner and the part does look new.

My question is - without that missing pointer, how do I go about setting the tension on the belt. I know that if it slips it's too loose - but over tightening it just ruins bearings in all sorts of expensive items like A/C compressors, etc.

Any suggestions?

In the absece of the pointer, all I can tell you is that you'll have to do it by "feel." Not too tight, but not too loose (though too loose is certainly better). Kind of hard to explain over the Internet.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

take a look at the tension on another car..... i usually push on the middle of the belt...and it should give about 1/2 inch with some pressure..

can't describe it here..but pretty obvious when you take a look...

it's kind of like setting front wheel bearings... just a certain touch..

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


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Middle of the belt between air pump and fan pulley? I think that's the longest open span easily accessible.

yes...i would say that "middle" is good... belt should be snug..but should have some play or give to it....

here's the way i see it---- if it's too loose it will flop.. if it's still too loose it will probably squeel when you step on the gas...

too tight is not good, IMHO

__________________
1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

Brian,

The pointer is a plastic piece that should be installed under the bolt that locks the tensioner down. It often does not get reinstalled, as it can be a bear getting bolt back in there with the limited clearance. They are available from the stealer for about $5 or so.

When you do get it installed, with the bolt still loose, set the pointer to the left-most line, and tighten the adjusting bolt until the pointer is between the two middle lines. If it cannot be tightened to the middle, check the tensioner per the CD procedure to ensure that it will return when deflected 30 degrees. If it doesn't, the internal rubber is sheared and it needs replacement. (Replacements do NOT come with the pointer!) If someone has overtorqued it without using the pointer, it could well be sheared.

While it's off, check the flats on the tensioner shaft for wear/deformation. You might be able to salvage a worn one by flipping the adjustment plate over and swapping its position with the spacer beside it, allowing it to sit on an unworn portion of the shaft. (Fortunately, the adjustment plate flats are symmetrical so you can flip it.

Gerry
87 300SDL
92 400E
67 230 <--- For Sale!

Thanks for the reply, Spook. It would figure that I was already at the dealer today. I never thought to ask if the pointer was available as a separate piece.

When you refer to lines - I assume that you're meaning on the actual body of the tensioner. There are 3 what I would call reference marks on the casting. The first and second are the left and right sides of a bar. The third is the point of an arrow. Hard to describe in print, but if I remember it right that's a good explanation.

The tensioner is new, so hopefully we don't have any issues with sheared internal components.

My main question is what causes the pointer to move? Is the hole through the pointer round, or does it have some keying shape to lock it to the internal shaft of the tensioner (which is what is being "twisted" as the tensioner bolt is tightened, right?).

Thanks again!

The plastic part has a serrated ID that fits over a "mild spline" on the center shaft of the tensioner. If the bolt is loose, you can set it to align with the left-most line. As you tighten the adjusting nut, (left-hand threaded!) the center shaft turns, carrying the pointer. Per the CD manual, there are five lines. It sounds like you have an arrow to start from, and then a range to set it in. Then torque the bolt to lock it in place.

Not a difficult job, other than the access to the dang bolt in the center of the thing, which on my 400E hits right on the "flange" of the fan shroud.

Gerry