[Lew]

This is what I remember reading regarding a broken crankshaft referring to a light flywheel. I certainly would take the author's advise in what he is saying in the last paragraph of this article.


WOW, this is one of the more extreme failures I have ever witnessed from any engine.... Its not too often that a crankshaft shears on the track on an engine that has 7 main bearings, but this one damn sure did!

The engine has the 3.6 X-51 package and was making 325 RWHP and had seen TWELVE THOUSAND track miles prior to this failure. We had initially thought the engine had broken a rod due to the material that came from the oil sump, but as soon as the engine arrived at our facility a 5 minute inspection found the crankshaft to be in two pieces!

The material these cranks are made from is powdered metal, it's what most modern engines use for crankshaft and connecting rod materials and I am less than impressed with it thus far. I can't believe that a component with such mass could break so extremely.

I feel that this failure was attributed to by a couple of things-

1- The engine was "upgraded" to a lightened flywheel. This new flywheel was installed onto the existing stock engine without being balanced to that assembly. This created an imbalance in the rotating mass AND it did away with the factory dual mass flywheel.

2- The dual mass flywheel was removed to alow the single mass lightened unit to be installed. This eliminated ALL MEANS OF HARMONIC DAMPENING!! The crankshaft was forced to absorb ALL harmonics from the engine and transaxle when the dual mass unit was removed..

So- adding the light weight flywheel was a double negative, not only did it create imbalance, it also eliminated the harmonic dampening of the dual mass arrangement.

Due to this I feel that adding a lightweight flywheel to any existing engine is not a wise decision, and that they should only be added when the entire rotating mass can be balanced and indexed to accomodate the lightweight unit. This means engine disassembly, so I'd only add one of these when doing one of our performance upgrades so the entire assembly can be precisely balanced.


Jake Raby