Thanks to George Fourchy:
The condition starts with the appearance of a soft banging sound from the front of the engine, which gets louder and louder over time. Slow deterioration of performance for no obvious reason follows over a period of weeks, and continues until the engine will barely run at slow speeds under load, while the banging sound gets louder and louder. Troubleshooting by using a stethoscope on the front of the engine results in determining that no component... P/S pump, alternator, water-pump, or either idler pulley...is making the sound. This determination was confirmed on the Lowrider by running the engine with both serpentine belts removed for a minute or two, while the stethoscope was used again to locate the noise within the engine. This was accomplished by removing the right front fender liner, and placing the probe of the ‘scope against the damper bolt while the engine was idling....this can be done safely, if one is careful and moves slowly, since the bolt is deeply concave and with pressure applied will allow the probe to stay in the center of the bolt head. The only place the sound could be heard through the stethoscope was when it was probing the damper bolt....nowhere else was it audible, even on the pan or oil pump housing.
This most likely will be the “crankshaft cancer” that first struck the Lowrider in the fall of 2000, on the way home from the Indiana SHO convention. The first symptom was a soft thudding audible from the right side of the car, coming from the front of the engine. I first heard it in late July, as I was letting the engine idle in a carport adjacent to a Super 8 Motel in Utah, after a long drive from Kansas. It got worse and worse during the fall, finally becoming REALLY loud in December. I finally took it to one of the SHOClub recommended dealers in my area, and the mechanic said to check the cam drive. I had already checked the idlers and all the accessories...I ran it in place without belts for a few minutes, and it still hammered. I pulled it apart over New Years weekend, and found 22 degrees of slop (cams were 22 degrees behind the crank....but it still ran!) in the timing sprocket and the woodruff key. I took some pictures of it (still have the old sprocket and key..pictures of them are included below), and fixed it using a new key, sprocket, and Locktite 640, the green stuff, for pulleys and shafts. There was .015 inch of wear evenly around the crankshaft under the gear caused by it rocking back and forth for all that time. The original cause was improper (none!) torquing of the crank damper bolt by the last dealer to ever work on my engine, changing the timing belt....4 years earlier! I cut a .015 feeler gauge into thirds and crammed the pieces under the new sprocket, along with the new key and Locktite. It went together just fine, and has been running perfectly ever since....now 75,000 miles later. I have been preaching to the list to check their sprockets whenever the timing covers are off....one can rock the engine back and forth with the alternator nut and a large ratchet or breaker bar, and watch the cam sprockets....if they don't move when the crank does, cancer is present. I got some crap from the SHOTimes list about being able to move the engine with the alternator, but I do it all the time. You only have to move it back and forth an inch or two to check for sprocket slop.
Many of our cars started having this problem over the last couple of years, and it has basically been caused by the failure to torque that bolt. The crankshaft timing sprocket is one of the few weak points in the engine....there should be more than one woodruff key, or the sprocket should bolt to the crank, rather than being single keyed to it. That one key is turning the equivalent of 3 four-cylinder engines' worth of camshafts, and it is very prone to failure (too much back and forth stress on the key from the timing belt, especially at low engine speeds) if that bolt isn't tight and the damper-sprocket sandwich isn't fully compressed.
If I had taken the car to a dealer to have them fix it, they would have told me I needed a new crankshaft, which would have effectively totaled the car. As it was, I fixed it for the cost of a feeler gauge (I had a parts engine), and that was all. (At the same time, I performed a full frontal 60K service.) A list member, Randy Crist, sent me the Locktite, and I've used it on a couple of engines in our local SHO club to repair the same condition, caused by the same loose crank bolt.