22 Jun 2022
Less than four weeks after installing the last round of goodies, went out and cleaned the car up, and we took the car on a 150 mile scenic trip





Really digging the freshly refinished wheels and the grey powdercoat! Anyway, the trip went well, until the end of the night. When we were less than 10 miles from home, the car began to run rough, and was missing on most of the cylinders. Check Engine light was flashing, and it barely wanted to idle. Got into a gas station, opened the hood, saw nothing obviously wrong. Fortunately, there is an Android radio in the car, and a bluetooth OBDII adapter in the socket for times like these.


OK, so my hunch was right. Lots of misfiring going on. Hit reset on the codes, and the car ran ever so slightly better, but a mile later, the CEL was on again, and we limped home. Checks under the hood revealed no obvious wiring issues. So, next guess was a bad ECU, let's swap that out. New ECU in, started the car, ran better. OK! Bad ECU. Time to call it a night. Went to go do some other maintenance the next day, and upon moving the car to the shop, CEL was once again flashing, and it was running rough. Uh oh. Put DAS on it, and..


Missing on half the cylinders. On different banks. At different ends of the engine. Weird. Open the hood at idle, and the supercharger belt tensioner is bouncing around like crazy. What the? Get a flashlight out, and one of my fears of all of these engines (M112 or M113) is realized. The harmonic balancer is wobbling. Have heard of this, was thinking it would happen to this engine one day. No sweat, I will order a 180mm crank pulley, and swap it, we'll be done. Hehehehe, silly boy!

First, the requisite week long wait for parts to come in, and then the fun. The handy, dandy M112/M113 crank holding tool fits the balancer in the car. Does not fit a revised contour of the new pulley. Grrrr.... Fortunately, work has a machine shop on the premises, the machinist took pity on me, and turned the tool in a lathe to that the edge off the tool, which now allows it to grab the new pulley. Perfect! Now onto the work. Put the crank holding tool in, got the 27mm 3/4" drive deep socket on there, breaker bar, 6' piece of pipe. Here we go! The pipe literally fell. I had to catch it to keep it from hitting the car. What the? Pull all the tools off, reach in, and remove the bolt with my fingers. Oh no! THE nightmare scenario for any of these MB engines had just arrived at my place. You see, this bolt it supposed to be tight. VERY tight. Essentially, torque it to 147.5 ft*lbs (200Nm), and then turn it another 90°. This pulls the bolt until it is so tight, and under so much load that it literally stretches the metal of the bolt out, causing a springing effect. I have no idea how much torque is on the bolt at that point. but it is a lot. This one came out with fingers.

This means, of course, the whole balancer is wobbling around on the crank snout. It means everything is galled up. In this case, it meant that the balancer did not want to come off the crank, at all. FIVE hours of pulling, prying, tool making, heat, dirty words, and a lot of sweat (It's been right at 100°F here in swampy Florida, lately), the balancer finally gave up the fight, and fell to the floor. Crank is galled, but not as badly as I would have figured. Crank key is obliterated. Pulley took the brunt, fortunately. It is trashed. Rubber for the pulley was fine. So what happened? In short, bad maintenance. At some point, this pulley was removed, whether to be replaced or front main seal, who knows. What is known is that the bolt was not properly torqued. When I see those YouTube videos of people putting this same pulley back on with an impact, well, this is what the end result will be. This failure was a ticking time bomb that was set long before I owned this engine. If you do not have the tools, know-how, or strength, stay away from working on the balancer on the M112(K)/M113(K) family. I think other MB products use the same setup. Frankly, it is a horridly bad design, and a real let down on MB quality engineering. I digress. There is a lot of work ahead.

Recovery is now the game plan. After cleaning up the remains of the crank key, polishing the crank snout, and some trial fits of the new pulley, the key was the next thing up that had to be dealt with. The teardown of a M112 engine sitting in the shop commenced. It was a shame to take apart an otherwise good engine, but it was the best option to get this car moving again. The key is visible with the balancer off the engine, but getting it out requires a tremendous amount of disassembly. After getting to about the 85% mark on M112 parts disassembly, I had a couple of thoughts:
1. This is a lot of work, and will be 10x worse in the car
2. You own a shop full of fabrication equipment. Apply a little fine "Southern Engineering" and fix this car - now!

And so I did. It's one of those things, where it's not stupid - if it works, so stay with me on this. The key, as intended, is only meant to locate the balancer on the crank shaft, to make sure it is indexed to the right location. The tremendous force of the main bolt clamps the pulley in place, and prevents it from moving. I just need to get the balancer located. Breaking out the MIG welder, a solution rapidly came into focus. A spot of weld, a little shaping and cleanup with a Dremel tool, and there we go! Actually, this part only took about an hour, and the only casualty was that poor M112 that I now wish hadn't been taken apart. It's ugly, I'll admit it. Not some of my best work, but at this point I was the better part of 20 hours into this ordeal, and has it been mentioned that it was 101°F out? Oh yeah, it rained. Then the sun came back out. It got hot again. Steam. Lovely. So, while basting in the sauna, this was the end result. It actually looks better, and more square in person, but the camera does what the camera does. More importantly, the balancer went back on, and indexed properly. A proper key will be dealt with then the engine comes apart in the future.

Eagle-eyed readers will notice the horrid abuse the timing covers was subjected to, in the struggle to remove the old balancer. Others will catch a glimpse of the next part. Before we get to that, let's talk about that key again. It's pretty wimpy. And the MB engineers knew it. The trick was that the bolt and its clamping force would take care of it. This is all carefully calculated by the MB engineers, but math sometimes fails lies. If there is a pulley change anywhere in the mix, then more twisting force is applied, and the chance that the bolt is not quite enough goes up. When it does, the key takes the brunt. Being made of a softer steel, and by design, meant to shear to fail, well, it does its job. People who add larger crank pullies encounter this rather often, and so many aftermarket solutions come with what is called a pin kit. These come in two main flavors. One has an insert that fits in the space at the snout of the pulley, and has its own key way that a square key engages a corresponding keyway in the new pulley. The insert has three holes in it that go all the way through to the face of the crank snout, all around the hole for that big main bolt. The installer drills through these holes, into the crank, and inserts the roughly 1/8" diameter pins into the snout. The main bolt hold the pins in, and now everything is more locked together. Other pin kits come with a jig that will put a 1/4" hole right at the interface between the crank pulley and the crank shaft. The result is that the pulley and the crank snout both have these half moon cutouts that when lined up forms a full circle. A hardened pin is pushed down in there, and the main bolt retains it. Makes it like a new, bigger, harder key. My UPR 180mm pulley came with none of this, as their experience said that, "If the crank snout is not damaged, then there really isn't a need for a pin kit." Well guess what?

After reading online, I found that M113K community legend Joe Ernst had devised a fix. Here's a link to it: https://stumptownbenz.com/pinning-th...ercedes-m113k/
In short, I replicated what Joe did, and it worked flawlessly! I cannot thank him enough for putting up this valuable info! So, you can see the half moon in the above pic, here's how it all turned out






Too many images. More in the next post.