Under Drive Pulleys - PeachParts Mercedes-Benz Forum

duxthe1 · #1 06-11-2010, 01:28 AM

Been a while since I had time to tinker with the Benz but I recently spent a couple of hours on the lathe to cut an under drive alternator pulley. I went with 72mm diameter. No real science there, the size of the blank was the determining factor. I wanted to slow it down pretty good though. My old 103 stays pretty wound up with my wagon's low gearing and doesn't do a lot of idling so I'm not expecting any charging issues.

My tensioner is getting old and I don't think it's got much life left so the pulley isn't going on until I'm ready to commit to a new tensioner, or conversely when the old tensioner fails. In the meantime I'm looking for an underdrive power steering pump pulley. I know I've seen larger p/s pulleys on the 601 or possibly non turbo 602 engine which should mate to my p/s pump. Hopefully the spacing is correct but I havn't confirmed it. Additionally I'm planning to put a seal kit in my p/s pump as it's been sweating a bit lately. So it will be a pretty big job getting the belt drive in order once I'm into it.

As I gather parts for the impending underdrive pulley swap / belt drive maintennance, I''l keep the pics coming.

taint · #2 06-11-2010, 07:52 AM

m102 2.0l - 2.5 16v have a bigger pulley on the power steering pump

gakz · #3 06-11-2010, 11:01 AM

Hmm.. underdrive pulleys.. maybe I shall consider this on my M111 engine?

duxthe1 · #4 06-12-2010, 01:06 AM

Thanks for the tip Taint. I'll definately expand my search. Now that I'm into the project I'm a little anxious to get it underway. The sooner I find the p/s pulley the sooner I can get it done, not that I'm real anxious to drop the cash for the tensioner

As for the M111, it could probably pick up a couple of HP underdriving some of the accessories. Since the 103's ground state is moderate overheating I'm only underdriving the alternator and power steering, leaving the fan and water pump to run at normal speed.

gakz · #5 06-12-2010, 03:05 AM

Powersteering and alternator are the only 2 I would probably underdrive as well on the M111.. we'll see how it goes I guess! LOL

duxthe1 · #6 06-14-2010, 11:26 PM

Taint you were right about the 102 engines having the larger power steering pulley. I snagged one at work today off of a junker. A side by side comparison confirms that the spacing is the same and should be a direct swap. Hopefully the extra diameter won't interfere with anything else. I've got my fingers crossed but I'm not expecting any surprises.

I took a pic of the stock pulleys and the underdrive pulleys for comparison.

duxthe1 · #7 06-15-2010, 08:21 PM

I installed the two pulleys today! The power steering was a pretty tight fit. Installed it has just over 3mm before it would interfere with the water pump pulley. There was a few tense seconds wiggling the pulley in place but that 3mm might as well be a mile b/c it does fit and work.

The alternator pulley was a simple swap. I unbolted the alt. and pointed it downward. Then underneath I just zipped the nut off with an impact and back on with the underdrive pulley.

I didn't loosen my tensioner, I just lifted the belt off of it He-Man style. The old belt was a 2415. The new belt is a 2475. It was just the right length that I could lift it over the top pulley and still have good tension. Better than the old belt by a little bit. I hope that doesn't do the tensioner in but we'll see. I know it doesn't have a lot of life left. Given the rush I was in to get the parts installed I didn't do the seal kit in the p/s pump. Those tandem pumps are a real PITA to re-seal and I wasn't in the mood after the day I had in the shop.

I've got a couple more pics. First is my charging voltage at idle, not a problem obviously.

Second and third are the pulleys on the car with the engine running.

gakz · #8 06-16-2010, 01:59 AM

So you made your Powersteering larger??? That makes no sense

duxthe1 · #9 06-16-2010, 02:17 AM

Yes, the p/s pulley is larger, therefore the p/s pump spins slower. Typically when underdriving, the crankshaft pulley is undersized. Not wanting to spin the fan and w/p slower I didn't go that route. When selectively underdriving accessories their pulleys are oversized which results in more degrees of crank rotation before one rotation of the accessory.

duxthe1 · #10 07-04-2010, 03:34 PM

Well, the new underdrive setup has several hundred miles without any issues. Battery charge hasn't been an issue, despite the slower speed of the alternator. Power steering is working like normal too. It still has plenty of assist at parking lot speeds. One difference I've noticed it that the belt doesn't slip when the steering is held at full lock. Before, it would chirp the belt a little to hold the steering on the locks. Since my p/s pump is a tandem pump I've been paying attention to my hyd suspension and 4-matic, too. No issues with either but I do notice that the hyd pressure release valve doesn't cycle as often.

I ended up making another pulley for a friend, who suggested I start producing them on a small scale. I've toyed with the idea but my biggest hold up is the amount of labor I have to put into producing each one. With a modest investment in tooling I could get the process to be a bit more efficient but I need to gauge interest before I commit.

So any of you guys interested in underdrive alternator pulleys? What price range would you expect / be willing to pay?

So far I have two "pattern pulleys" to copy the spacing from. One is the 103 pulley which applies to the 104 as well. But not the 8 rib 104 setup. I suspect it would interchange with all of the 60X engines as well as the 102 but havn't confirmed those past a quick visual. My second pattern pulley is from a 119 (6 rib) setup. It appears to be the same spacing as the 112, 113 engines. I'm sure that this pulley applies to a few other engines but again not confirmed.

gakz · #11 07-05-2010, 02:10 AM

I need M111

duxthe1 · #12 07-05-2010, 02:20 PM

If you can take a pic of the pulley from underneath we can see if it matches one of my "patterns".

gakz · #13 07-06-2010, 01:56 AM

What do you mean.. underneath?

duxthe1 · #14 07-06-2010, 01:30 PM

As I recall the alternator is not very visable in the supercharged engines. Underneath would probably give a much better view.

duxthe1 · #15 07-10-2010, 04:56 PM

I got a peek at a N/A 111 engine. It's pulley matched a third pulley I have that has the same spacing as the 103 pulley but is machined a bit differently. The only differences are superficial. I'm not sure but I'm suspecting that the differing pulleys with the same spacing may be the difference between whether it's a Bosch or a Valeo alternator that it came on. I also noted this same pulley on a 606 engine. So far as I've seen, all of the inline engines share this pulley spacing. To date all of the "V" engines share the other pulley spacing, too. The supercharged engines are the ones I'm not sure about. I've never paid any attention to how M/B deals with the additional belt drive on those.

Given the tedious nature to cut the pulley profile with a single bit, I'm starting work on making a hob style cutter that can cut the entire profile at once. That will be quite a project in itself not even considering making a drive system for it. The payoff will be transforming hours of work into minutes.