Alternator replaced.

Gabe Athouse

New member
Well that wasn’t the cheapest or easiest alt I’ve ever swapped out, but I got er done. I wish merc hadn’t used those damn 6 point bolts everywhere. Those are weird and uneccesary imo. Speaking of which I have the special sockets for them, but I seem to always make do with box wrenches when needed, do they make box wrenches that are for these type of heads?

I opted for a factory replacement 150a new Bosch unit, which will match my new sealed flooded Napa battery.
Question, is the serpentine belt tensioner supposed to be spring loaded or does it have a lock down bolt that I can’t seem to see? I just forced it loose and then tight again, but if it’s supposed to be springy then it’s not.

Btw I paid 185$ for the new unit on amazon, and it came with official looking Bosch paperwork in a Bosch box so I feel good it want a scam unit. It also came with a lifetime warranty? So I filled out the card and sent it in. Why not? Dunno if it will work or how I’ll even remember I have it but that’s the story there.
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Erratic Member
Yes, the tensioner is spring loaded.

It does NOT have a lock-down bolt.
It has a 3/8" square hole to accept a ratchet wrench square pin to assist in removing the tension on the belt during replacement.
Drawings and discussion in section 7, pages 7 and 8 in the 2006 service manual.


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2004 140” SHC U.S. T1N
The belt tensioner is spring loaded and should move freely. Replacement is straightforward, though you’ll find two more bolts to use your E-torx sockets on!

The tensioner is shipped with an 1/8” locking pin that positions the arm to make the two mounting bolts easy (easier?) to get at.
I used a pop-rivet shank to lock mine open for removal, but it doesn’t sound like you’ll need it?

When the pivot siezes your belt will slip and you’ll get faster component wear, etc. When they’re poorly made they can fail catastrophically... My OEM was a Litens (which seemed okay when I followed a recommendation to replace it while I had the rad fan off at 180,000 miles). I would personally avoid castings by INA after seeing this thread:



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Gabe Athouse

New member
Cool thanks. Yes I was getting some belt squeal now and then so it seems im shopping for a tensioner. Is there a preferred model?

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