Broken DMAX CRANK

[Robyn]

Well, Missy here rarely gets to the DMAX forum, but I got my peepers on a Broken crank in a DMAX today.

The engine is a 2004 from a GM 5500 passenger coach.

Making bad noises :eek: and metal in the oil.

My buddy is repairing it for the transit company and plans to remove the crank 0nly and replace it with a good used one along with bearings, seals and an oil system flush.

The pix was shot from my iphone a couple hours ago.

I thought 6.5's were the crank tweeker queens, but I guess these can too.

TO THE MODS, YA MIGHT WANT TO CORRAL THIS AN ADD IT TO THE "IT CAN HAPPEN FILE"

Missy

[Kennedy]

Yes it can happen. It's somewhat rare though and typically can be attributed to bad or imbalanced injectors. Had one break here on the dyno with aftermarket injectors in it. Injectors later tested and found to be WAY out of balance. Many, many, many Dmax stock cranks running at 800, 1000, and more RWHP w/o issue.

[Robyn]

That makes sense.

Maverick and I were discussing the subject last night and the rarity was mentioned.

I have no idea of how the thing was cared for or maintained, so I can't say anything there.

I just had it in my head that the Dmax was "nearly indestructable" in that area.

I am a firm believer that injector issues have much to do with 6.5 crank failures as well.

Cylinder imbalance can certainly cause a ton of extra stress on things.

Missy

[More Power]

Cylinder imbalance can certainly cause a ton of extra stress on things.

Missy

It's interesting that the crank didn't fully separate and break the block.

Sure, anything that takes the dynamics out of the norm can cause problems - though rare.

One big difference regarding injector imbalance-produced engine failures between the 6.5 and the Duramax is the nature of the fuel injection system.

The 6.5 uses a positive displacement injection pump that uses pumping plungers, meaning the pump can only deliver a small preset volume of fuel to a given injector per injection event. There's much less chance of a bad 6.5 injector causing a crank failure.

The Duramax uses a high-pressure common rail system, meaning a failed injector could deliver a much larger volume of fuel per injection event. This could cause that cylinder to hit hard - very hard at each combustion cycle regardless how far the accelerator pedal is pushed. Holed pistons have been a result as well.