Turn 2 at autocross on my 5th run of the day at 6,000 RPM's I hear a loud grinding noise and then my engine siezes.

long-story short the counterweight on the flywheel came loose and wedged itself between the flywheel and the starter.

Upon closer inspection, of the 4 spot-weld spots allocated, only one was actually spot welded, and after 150,000 miles it decided it wanted to come loose.

Welded it back on securely enough to get me back home, could definitely tell when it was off of there, the engine out of balance shook like crazy, hopefully the journal bearings and rear main seal are ok... going to have to get another flywheel with a 0-balance and put it on there now because I'm sure the welding job threw off the weight and location a bit, but needed it to drive back home anyways....

something to be aware of in case anyone else is still running the stock one....

 

I don't think I have ever seen a thread about a flywheel weight coming off. Seems rare. Gotta be lots of people out there turning 6k on a stock flywheel without issues.

 

I will be checking my flywheel when I get it back from the shop.

 

umm, you don't want a zero balance, unless the crank has been balanced to zero with heavy metal, your flywheel with the weight off was near zero balance

 

hmm... its been years since it was rebuilt.... but that seems incredibly strange to me....
I can't believe a machine shop would have been stupid enough to not internally balance the rotating assembly and instead rely on an imbalanced flywheel to meet an externally balanced spec when it was doing the work before assembly....

Ahh, the stock GM motor is internally balanced up front with a zero balance damper, and externally balanced in the rear by a weight added to the flywheel.... how inept...ah the things I forget after all these years.

guess that's kind of important since I need to go out and buy a new flywheel since I'm sure I'm off by about 40 or 50 grams.
I presume the stock flywheel will have the same balance weight on there and be fine, the stamping showed a mid 700 something number, I assume this was grams of weight, and I'll assume that under 400hp the stock flywheel "should" be fine, presuming that it was tack welded correctly

 

Any suggestions on a brand or part number for a better than stock flywheel with the proper external balance, perhaps some weight loss for the rotating assembly as a whole with that for under $100, or should I just get the $30 from a local parts store and be done?

 

I bought a better-than-stock billit steel flywheel with the factory external balance at a clearance price, and you can get them....oh wait...

...never mind. Inept. Hmm. I don't wanna help anymore.

 

I won't go to bat for a bad design.
A well-built engine that will last to 100,000 easily, performance or not, is properly balanced, internally first, and then externally. Anything else is a short-cut.

 

There is no such thing as internal AND external balance. ALL GM motors with a one piece rear main seal are EXTERNALLY balanced from the factory.

Let's also answer a misconception regarding the balancer. As quoted from

http://www.automotiverebuilder.com/ar/ar99928.htm

"HUB AND BALANCER
The balancer is a two-piece assembly with a pulley that bolts onto the hub. Separating the two made it easier to install the Optispark distributor on the assembly line and out in the field. The holes in the hub are offset, so the balancer only fits on it one way, but there’s no keyway in the hub to index the hub on the crank. This shouldn’t be a problem unless the damper was drilled at the factory to "trim" the final engine assembly.

If it was drilled a lot to compensate for an engine that was out of balance, you could end up with a shaker, depending on how everything stacked up with the remanufactured engine compared to the original engine. If you encounter a balance problem on a remanufactured LT1, try rotating the balancer assembly on the crank 90° at a time to see if it eliminates the problem."