Fan Belt Tensioner - Mercedes-Benz Forum

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post #1 of 1 (permalink) Old 03-02-2012, 01:42 PM Thread Starter
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Date registered: Jun 2009
Vehicle: 1955 300 SL
Location: New York
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Fan Belt Tensioner

Some Mercedes-Benz engines (including the 198) employ a very positive screw arrangement to provide proper tension for the fan belt. As I have been missing parts of this assembly since I got my car 40 plus years ago it finally seemed appropriate to track down replacements to make everything whole. The costs quoted for M-B parts were shocking, so it became time for some creative thinking. In essence, what was needed was a threaded type device and an eyebolt (swing bolt/hinge bolt) that would extend as the device is rotated, thereby tightening the fan belt.

A few minutes spent at the local hardware store turned up a 3/8-16 coupling nut 1¾” in length and a 3/8-16 thumb screw 2¼” in length. The raw materials were in hand.

Some work with basic metal working tools reduced the size of the coupling nut at one end so that it would rotate freely around a mounting stud affixed to the engine block. The threaded interior of the coupling nut must also be drilled out to a diameter of 7/16” for a depth of approximately ¼” to accept the mounting stud. Similarly, some small grinding and drilling of the thumb screw quickly produced the functional equivalent of a commercial swlng bolt at much reduced cost.

For those considering such a repair/replacement, be advised that the purists may decry the use of a non-metric thread size, but 3/8-16 is so close to that which was originally used as to be indistinguishable, and the entire project was completed at a cost approximating 3% of that which was quoted for M-B parts.

Last edited by ejboyd5; 03-04-2012 at 07:26 AM.
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