I recently had to change my distributor because of a screeching noise and vibration coming from the top of the distributor shaft. The noise was LOUD! When I took the cap off, the upper shaft (where the rotor goes) had alot of play in it. I've never seen a distributor go bad like that before. Anyone have any idea what would cause this?

 

Probably just the bushings inside worn out, I had a bad distributor in my S10 truck too. GM isnt known for having low tolerances and perfect balance inside the engines and components. Lots of thier products have a balance shaft inside the engine to balance out the shaking that would happen from components that are "good enough" to assemble... think there is a balance shaft inside anything made by Ferrarri? Nope, cause "good enough" for Ferrarri is perfect. I saw a really interesting show about ferrarris factory on TV before, they are amazing automobiles. Everything about them is made on site, the only thing that rolls in their gates is raw materials - rolls of leather, train cars of ore for casting... they make EVERYTHING for their products. Ferrarri pistons and rods and valves are exactly the same weight as each other down to ten thousandths of a gram, their paint is the same thickness everywhere on the car too, they even have trees inside the plant to keep the humidity levels the same, they are truly awesome machines, i hope I can own one some day.

Its like when you look at a brick wall. There is thousands of bricks there, but you can find one or two that are cracked in that wall. Same thing happens on the distributor shaft assembly line I guess...? Once in a while one fails. I dont know if anyone will know why they fail. I personally think that they are built with good enough quality so they can sell more replacement parts!

 

I guess it's a good thing I have a parts truck! LOL

 

Things fail for unknown reasons all the time. Could have just been a bad shaft or could have been someone doing something incorrectly sometime in the vehicle's life. Hard to say. Check over the replacement one before you drop it in.

And now for a little diversion from the topic just to clear up some misconceptions about the balance shaft...

The balance shaft was not installed to correct for out of balance assemblies or lack-luster tolerance holding, it was there to cancel out unwanted vibrations from the design of the engine in terms of firing order or, more correctly, power stroke distribution.

The optimum bank angle for a v6 is 60* which will allow the pistons to fire at 60* increments keeping power stroke occurrences balanced. By using a 90*V engine, the power stroke pulses happen at 90* increments. For a v8, this is ideal, but for a v6, not so much. For every revolution of the crankshaft, 3 cylinders fire off at 90* intervals with the final 90* being empty. The balance shaft counters this empty space, smoothing out the operation of the engine.

Even with a perfectly balanced rotating assembly on one of these engines, you would experience a rhythmic vibration with some additional excitation at particular RPMs depending on the rigidity of the system (motor mounts, trans mounts, etc). The design could have changed to a much more expensive crankshaft layout to separate the pistons allowing for an even 60* offset in power strokes, but it is easier to put a balance shaft into it. Besides, these engines are damn reliable. I wouldn't recommend them change a thing.

I typically don't like linking to Wikipedia because there are often inaccuracies in their data, but THIS PAGE explains the function of a balance shaft.

 

Interesting fact and that makes perfect sense. I guess thats why Ferarri V12s have such a tight V design then, like 30 degrees...

 

All I can say is this, I paid $400 for my truck 4 years ago... try finding a Ferrarri of ANY condition for that price! I'll replace 10 distributors if I have to... my truck owes me nothing! Besides, GM did something right. I've got over 140k on the original, (never been rebuilt) motor and I can't seem to kill it and believe me... I'VE TRIED!!!!! In fact, it runs better today than it did when I got it! Gotta love General Motors!