Serpentine Belt Tensioner Heads-Up

[CruisnDiesel]

I hope this thread isn't too cold, you guys really got my attention. My 2004 647 has almost 100K on it, and the battery light has been flickering on and off. I took a look at the belt, and it and the tensioner look like the fluttering bad example in the videos above. So I have been reading through this great forum contemplating my next steps. What I could see of the belt looked pretty good, but it is the original. I bought a spare belt from europarts five years ago. It is a Contitech PN 6 PK 2260. Different than the number Vanven had in post 29 for the 647. Would anybody else like to weigh in on the correct Contitech PN for a 647 belt?

I need to decide how deep to go, so I will look to see if the water pump is leaking, check the alternator pulley, maybe check for reasonable torque and smooth movement in the tensioner, look for any breakage in the idler, and replace only with MB parts! This is a passenger van with the aux rear AC, so there are two condensors in front, and a second small cogged V-belt in front of the serpentine. I will check the tensioner and replace that belt also.

In post #37 Steady-Eddie mentioned replacing the pulley on the alternator. Where can you get a replacement alternator pulley? I read in another post that MB only sold the complete alternator. I assume that there area couple special tools involved in removing the pulley from the alternator.... is that correct?

Thanks for any help ...

[talkinghorse43]

Sounds like you need a new alternator. You could just change the pulley, but it doesn't seem to be a good investment to me since when I checked the parts (w/o tooling to change it) were ~$80. Go to Europarts-sd.com for a new Bosch. Wouldn't hurt to check out the rest of the serpentine belt path for damage while you're at it and install a MB original belt, but probably its early at 100k to change other parts out if they look OK. For the second AC compressor belt & tensioner, check current threads for recommendations. The good Doktor recommends Sprinters like yours with the dual belt harmonic balancer (crankshaft pulley) have their pulleys replaced every ~100k miles to ward off a catastrophic failure that could doom the engine or tranny.

[CruisnDiesel]

Talkinghourse43 thanks for the pointer to the HB problems, I spent a few hours reading through that thread getting educated on that problem, not sure what I will do. I too saw the good Doktor's 85K mileage replacement recommendation. Failure of the HB is bad for sure, but I can't tell from all the posts if my T1N is at high risk or not. I only haul kids with it, so it has never been overloaded, but it does have aux AC. I inspected the HB, it has the older bolt, and no cracking that I could see.

[seans]

Originally Posted by CruisnDiesel

I hope this thread isn't too cold, you guys really got my attention. My 2004 647 has almost 100K on it, and the battery light has been flickering on and off. I took a look at the belt, and it and the tensioner look like the fluttering bad example in the videos above. So I have been reading through this great forum contemplating my next steps. What I could see of the belt looked pretty good, but it is the original. I bought a spare belt from europarts five years ago. It is a Contitech PN 6 PK 2260. Different than the number Vanven had in post 29 for the 647. Would anybody else like to weigh in on the correct Contitech PN for a 647 belt?

I need to decide how deep to go, so I will look to see if the water pump is leaking, check the alternator pulley, maybe check for reasonable torque and smooth movement in the tensioner, look for any breakage in the idler, and replace only with MB parts! This is a passenger van with the aux rear AC, so there are two condensors in front, and a second small cogged V-belt in front of the serpentine. I will check the tensioner and replace that belt also.

In post #37 Steady-Eddie mentioned replacing the pulley on the alternator. Where can you get a replacement alternator pulley? I read in another post that MB only sold the complete alternator. I assume that there area couple special tools involved in removing the pulley from the alternator.... is that correct?

Thanks for any help ...

Wow - sounds a lot like what I'm in the middle of. See this post I made today on the water pump replacement thread.

(from that thread:)
tornapart.jpg

I'm replacing the alternator, belt, tensioner pulleys, and I'm considering replacing the water pump and other hoses. I have non-OEM parts and am considering doing a temporary repair now and a permanent full repair (replacing the non-OEM parts with Mercedes parts) in the spring when it is warmer.

If you follow the instructions from an earlier post (which I've linked to in my post) you will find that by removing a lot of parts including the bumper, you'll have a LOT more room to work and inspect. I found I had to remove the turbo resonator to get to the top alternator bolts, and this would have been a LOT easier if I had moved the radiator first.

I want to, but have stopped short of removing the transmission cooler lines to swing the radiator out (per the instructions mentioned in the link above). I have never pulled them before but there are a number of threads where people are complaining of transmission fluid leaks at the radiator. I really want to get a better view - I think I might have a weeping water pump seal - but if you remove the wrong fittings you might be asking for trouble aka replacing the radiator. More people need to weigh in on this. See talkinghorse43's posts adjacent to this one (which is just before the other post and includes my guess of which are the danger fittings.)

Can you please post a link to the Doktor A 85K mile maintenance item post?

Thanks and good luck!

[CruisnDiesel]

I think I read through some earlier posts on the 647 water pump replacement thread. Looks like you are pretty far into it. It is tough to decide how far to go with replacing parts while you have easy access. I haven't seen any indications of leakage from my water pump, so I may just replace the belts and alternator for now. I think I can do this from underneath without taking much else apart. I see you also have the Aux rear AC compressor. Here is the link to the Doktor's 85K suggestion: http://sprinter-source.com/forum/sho...&postcount=145
Sorry best I could do on the link ....

[MightyGopher]

Thread kinda got lost in the facts. The Dr. is 100% correct. I replaced my OE tensioner at 236K because it had a little slop in the wheel. Do not use any tensioner that is not MB or Litens. Dayco sells the same tensioner as europarts, mine fractured at 12K just exactly like Talkinghorse. Napa sells the litens OE tensioner for a few bucks more, but well worth it. The dayco model will leave you stranded without warning and if you do not notice the missing belt, perhaps a engine!

[Coast2Coast]

Just got off the phone with the local Mercedes Sprinter dealer in Westminster they said the OEM Idler Pulleys are made by INA and the Tensioner is made by litens.

Anyone had any bad luck with INA Idler drive belt pulleys (qty) 2 ? as shown in link below

http://www.eurocampers.com/2001--200...red_p_542.html

[vanven]

Originally Posted by talkinghorse43

Continuing...

The ends of the spring shown in the exploded view in the post above fit into recesses in the tensioner body and the inside of the top of the tensioner to provide torsional resistance to pivoting. The spring is also compressed on assembly and provides clamping force to hold the back plate in firm contact with the plastic insert. This effectively makes the back plate/plastic insert a brake or shock absorber, apparently meant to dampen oscillations. I haven't disassembled the OEM Litens brand tensioner because I plan to use it as a spare part in the future, but experimentation with the torque wrench shows me there is no such damper in the Litens brand tensioner. The 1st pic below shows the top of the tensioner body and the cavity for the central spring. Also, this shows the top sleeve bearing for the central shaft. Again, this bearing appears to be coated with PTFE, which is partially worn away.

The last pic shows the central shaft attached to the top of the tensioner. The surface of the shaft in contact with the two sleeve bearings is corroded, which accounts for the increased pivoting torque and the overload failure of the roller mounting arm. Note also where the shaft meets the top of the tensioner. It can't be clearly seen, but an O-ring like the seal at the bottom is also fitted here. This is where I believe the water responsible for the corrosion of the central shaft entered. Since the design of the tensioner depends on the friction between the back plate/plastic insert to provide damping, that friction pair will lose thickness due to wear which will remove the top O-ring from contact with the sealing surface (top of the central tube of the tensioner body) allowing the seal to be lost.

Therefore, the very design of this tensioner dooms it to early failure.

Thanks to this analysis Europarts-sd (Steve) emailed me to offer me a free replacement for my INA (second one). He did this w/o me requesting it. Thanks again talking horse.

[SRT2]

Originally Posted by abittenbinder

When a belt tensioner does not pivot smoothly, in spite of heavy spring tension, it MUST be replaced.

Easy to evaluate with a long flex head wrench w/17mm, 12 point socket, from under the vehicle.

Beware of aftermarket tensioners.

Doktor A

While I have "strayed" when replacing A/C compressors, power steering pumps, and alternators, I will only use OEM Mercedes parts for the tensioner, water pump, and idlers. Nothing shuts a truck down quicker than chucking a belt, and keeping the correct tension is a must. Good advice, Dr. A!