427zm

iTrader: (9)

Ok, so as the title says, can a hung injection cause a crack to break? This isn't specific to the LS, it's more of a general engine question.

The reason is ask is at work, we had a customer that broke their crank on a motor (Huge Diesel Motor in a Mining machine) and they believe it is due to a bad injector that hung open.

The more I think about it, the less I think this is possible. The only way I could see this happening is if the injector hung, caused the engine to overrev for an extended period and break the crank. In this particular mining truck that would mean someone would a have a serious wreck with a runaway truck. That is not what happened.

So my question is to you savvy engine guys out there is this possible? Have you seen it? And what causes the crank failure in the end?

David Q

I guess it could hydro-lock the motor causing the piston/rod/crank failure.

3rdCoastPowerSports

iTrader: (5)

typically when you hydro lock the motor you bend a rod or blow it out the side of the block but its the rod that usually takes the hit.

427zm

iTrader: (9)

We'll know more when we get it apart, but it didn't throw a rod. We'll also be checking all the injectors and their fuel as well.

96capricemgr

iTrader: (1)

Did it break running or starting?

I don't really know anything about diesels but depending how much momentum was built up in cranking the engine before a cylinder full of fuel hit compression is suppose it is plausible.

For it to break running I think you are right about how that would have to happen with an overev. I just don't think there would be time to fill a running cylinder with enough fuel to hydrolock with a stuck injector.

You said a runaway engine would have meant a runaway truck, no neutral, low gear etc. that would allow control to be retained while an engine overrevved?

Could have been a manufacturing flaw in the crank that survived till something else went slightly wrong??

bmax

iTrader: (1)

Good luck with it.

slamminjim

iTrader: (6)

It would fill the crankcase with diesel before it broke a crank and it would have spun main bearings
I would think. I have seen a semi have a hung injector and this was the outcome.

Z28Drifter348

Yes I would believe that the crank broke because
the injector stuck open and the crank broke upon startup, But for this to happen while runnin is next to impossible,especially if it is a mechanical injection system common rail system it might be possible but very unlikely. If this happened while the engine was running and it is a mechanical injection system I would believe its a timing issue with the injection pump. Pre detonation is dangerous on a gas motor but it's pretty much fatal to a diesel if the injector fires before TDC. Especially if the charger was cranking and the driver was in the throttle hard. Imagine the piston half way or almost all the way up on its compression stroke and it gets smashed dead on with a sledge hammer.

BigRich954RR

iTrader: (1)

i kinda feel this is what happened. cause on these big diesel the tq per cylinder is high

427zm

iTrader: (9)

It's a mechanical injection system, and recently, both fuel pumps were replaced, but the injectors werent checked. We believe it happened while running, but we aren't sure. We should be disassembling the engine next week.

427zm

iTrader: (9)

Yes, neutral could be used, but these trucks carry between 120-150 tons of material at a time, a retarder is used ALL the time along with the brakes. Pulling it into a low gear would end up with a bag of parts for a Trans and a runaway truck.

427zm

iTrader: (9)

It is obvious we MUST find out if this thing was running during the event, or if it was upon startup. We think it was running, but again, I can't confirm it. As for the driver, there is basically WOT and idle.

427zm

iTrader: (9)

I can't get a pic to load for some reason, google image a "QST30". That's what we're dealing with.

427zm

iTrader: (9)

Good to know.

Z28Drifter348

I was thinking more about this the other day. I'm not 100%sure behind this theory but if the injector failed while the de compression brake was turned on this might cause enough of an imbalance across the crank that it could have caused such high harmonic vibrations the crank gave out. Just a thought.

427zm

iTrader: (9)

Thanks for the info. An update will provided probably early next week. We should have the motor tore down and injectors will be checked by then.

sreve

iTrader: (3)

Diesel engine runaway can happen easily when it finds a new source of
fuel. A leaky turbo or blower seal that blows out will allow the motor to
burn engine oil feed to it under pressure. The govenor will not save it

Truck drivers don't tell on themselves

427zm

iTrader: (9)

Yes, we have seen it happen, to the point of burning a machine to the ground! I will say again though, that is not what happened here. Nothing burned up, and there was no incensed with the truck.

Vexzer

iTrader: (1)

hydraulic'ed