2003 E53 M62TU Alternator Belt Tensioner Question/Observations

[tempest411]

Hello,

I started out intending to just change the radiator and a few hoses, but in typical fashion other things were discovered along the way. When I had the radiator out I thought to myself 'gee, it sure does look like it's be easy to swap out the belts the way it is now', and that brings me to what I'm posting about now. I noticed when I backed out the bolt to release the tension that the arm hardly moved at all. I immediately assumed the tensioner was bad and ordered a new one along with the belt. Upon assembling it today I was surprised to see it wasn't really any different going back together. There also really isn't that much travel in the mechanism, even without any belt in place at all. I would expect the mechanism to be able to swing through it's full travel without a belt in place, but it doesn't the lower tension pulley hits the crankshaft pulley. With a belt in place, and it's a pain to put on, the adjustment/tension lever sits at nearly the end of its travel even before the strut has put any tension on the belt. Using a 17mm wrench to turn the lever, it only swings through about 10 degrees before running out of room in the adjustment slot. I've got it set there and am confident it will work, but only just. Have any of you made the same observation?


A couple other things I noticed...There appears to be TWO different adjustment/tension lever designs out there. One in TIS, and the other in photos of parts actually produced, as the example on my own vehicle. They are both identified by the same part number, 1128745904. When searching a reason for why the tensioning mechanism worked so poorly I thought I'd discovered that my vehicle had the wrong part in place. But any other picture I found of these matches what I have. I attached pictures of both designs to illustrate what I'm talking about. Basically, the two differ in that the pivot and clamping bolt positions are swapped.



Also...There is a TON of tension on this assembly! When I first tightened the tension lever down I did so at 15 ft-lbs, which is the normal torque for an 8mm bolt anywhere, but the lever would slip as soon as I took the 17mm wrench off it. It wasn't until I read that it requires 22 ft-lbs of torque on a grade 10.9 bolt to insure it stays put. That's a very bad design! I can't help but wonder how many people have stripped out the bosses in the timing cover, or if any of those mounting bosses have broken off over the years.



Lastly, the listing I found on many websites will direct you to use the wrong belt on the alternator. The first number I got was a Gates K070644, which is equivalent to a 7PK1637. The correct number is a Gates K070640, equivalent to a 7PK1635. I am more than sure the extra 3/8" of the longer belt would've caused me grief considering how little room there is for the mechanism to work. Attached are pictures that will hopefully communicate everything I'm talking about. I can't help but wonder if there isn't something I've gotten wrong...Or maybe it's just a bad design.

[Henn28]

Seems like you’ve got it right, from what I recall. I will note that I bought a complete tensioner assembly, was in a hurry and threw it on, only to have the belt disintegrate at highway speed due to nut “14” (if I recall correctly) being under torqued and contributing to a very slight pulley wobble. Buyer beware I guess. I agree that there isn’t a lot of adjustment “arc” in the part, but it seems to do the job.

The 4.6 and 4.4 belts are of slightly different sizes to accommodate the underdrive balancer on the 4.6. Maybe the vendor you are pulling the part numbers from confused them? The same vendors above sent me the 4.4 belt with the kit, rather than the 4.6 belt I ordered. Luckily I caught that mistake. Or maybe it would have failed immediately and saved me the trouble on the side of the road if I had missed it!