The Duramax Crankshaft Failures.
And How to Avoid Them.

Lets talk about your problems…..

The 6.6 Duramax Diesel Engine has been a fantastic platform since its conception with the LB7. Most manufacturers have had a lot of different changes with their platforms. And though the L5P is by far the most changed of all the GM 6.6 Duramax Diesel Engines, it still hasn’t seen a displacement change.

Though there have been many variations of the engine, some of the same problems have followed each one. Two major issues that have plagued the 6.6 Duramax Diesel engine, strike fear in the owners. And that is because when either one of these events takes place, they mean catastrophic failure of the engine. Though the 6.6 Duramax Diesel is a true contender in the performance arena, it is evident that the failure can take place at any power level. We have seen many stock LB7, LLY, LBZ, LMM, and LML engines succumb to such failures.

There are some things about the 6.6 Duramax Diesel Engine that make it susceptible to the crankshaft failure. Though many would tout security in the alternate firing order camshaft, we have seen failures with engines running them. The LB7 through LML Duramax Diesel crankshaft has a smaller journal diameter at roughly 3.145 diameter. The water pump is driven by gear from the crankshaft. This is common practice on larger diesel engines. But these engines will also use much larger crank journals in industrial applications. When water is being driven by the impeller, it sends this pulsation back to what is driving it. There is a frequency that is induced back into the driving crankshaft.

 “A whole lotta’ shakin goin’ on!”

 Everything oscillates at a frequency, all things in nature. But what becomes very dangerous is when things begin to find a resonant frequency. Or a natural frequency where a medium vibrates at its highest amplitude.

A few weeks ago, we had a machine cutting tool manufacturer come in for us to sample some of their boring bars. The part we were working on was a sleeve. Although we had “pie jaws” to hold the cylinder shaped sleeve. We still fought “chatter” as the part thinned out. There are many different types of boring bars made, and they are made from different materials. Each material oscillates at different frequencies. So long as the material you are cutting, and the tool you are using do not match up in frequency, they won’t achieve the nasty harmonic that we know as chatter. This eventually led to the failure of the boring bar, as seen in the photo.

Now, what does all that mean? That is the best example of why a GM 6.6 Duramax crankshaft fails that I can give. There are a couple things to do about this. The biggest thing is not to get excited, no seriously, well maybe not you, but your crankshaft. The engine is rotating about and the crankshaft is twisting because every 90 degrees of the crankshaft rotation, a detonation is taking place. This is extremely violent! If we can maintain the frequency to a more manageable rate, we can help it live. 

Balance is the key to life…… or a happy engine anyway…

How are we able to do this? Through balancing! I cannot begin to express the importance of balancing in an internal combustion engine. Keep in mind the crankshaft stores this energy each time a combustion event takes place. It has to release it somehow and somewhere. That is the reason for the harmonic damper. Think about that word we just said a minute. You may not truly think about what its job is. Sometimes it’s referred to as a harmonic balancer. While it is true that it does balance the externally balanced engine, that isn’t its whole job. That is the reason it is so important that when you are rebuilding your engine, or buying a reman engine, that you replace the harmonic damper. 

But here is where it really becomes even more problematic with buying a remanufactured engine. Most engine rebuilders don’t balance the engine. Crazy, right? I know. But it’s the dirty little secret that I have seen more engine builders try to downplay. They use the argument that because it turns slower than a big block, it isn’t needed. Which frankly is straight ignorance. 

Your grandmother’s ceiling fan turns slower than them both. But remember watching that 3 out of 4 bladed fan swing wildly in the wind as a kid? I sure do. It was exciting, and fun to watch as a kid. But not really something I would enjoy thinking about in my engine. What makes this worse is the fact they bore the cylinders larger and put bigger pistons in. Larger than the factory pistons. Which means the factory balance job, which isn’t balanced all that well to begin with, is now even farther out of balance!

 So this aggravates the condition, and makes the chances of crankshaft failure even higher. If your engine is running right now, you’re not in the market for a reman engine. But there is something you can do to help with your current condition. If you are in the market for a remanufactured duramax diesel engine, NOW is the time to be educating yourself about these things. Asking the right questions. And making sure that not only does your builder claim they are balancing your new engine. But they also can produce a balance sheet when you receive your reman engine. At Choate Engineering Performance, we include this in all info packets when your new duramax engine is shipped.