Broken Rod And Bent Push Rods......

[kdixer]

too much timing from a custom tune can hurt rods

 

How?

 

 

Too much of the burn cycle will be complete before the piston reaches TDC therefore the connecting rod will be exposed to extreme pressure as the crank continues to move the piston upwards. The burn cycle is supposed to work with the momentum of the crankshaft. If the fuel mixture is ignited too early it will fight the momentum of the crankshaft. The weakest link between the crankshaft and piston is often the rod and sometimes the wrist pin. The explosion can be compressed to an extent, but the connecting rod and wrist pin are not strong enough to compress the explosion created beyond a certain amount of fuel. The time it takes from the point the spark plug sparks and a certain % of the fuel mixture is burned is set by the ignition timing. Ideally you want maximum cylinder pressure to be achieved right as the piston reaches TDC or cycles slight past TDC. This way the piston is propelled downward with as much force as possible creating effecient HP. If the timing is too early, too much of the fuel mixture is burned before the piston reaches TDC. You have to visualize the fuel catching on fire and understand that it does not just combust in a uniform manner. The flame usually starts at the spark plug and spreads throughout the combustion chamber. We are talking milliseconds but the fire spreads, it does not just appear.

[donjames911]

I would love to see pics of the engine. This sort of thing is what I really liked about being a mechanic. Trying to figure out what happened.

That "bug on the screen" avatar is way cool!

[wavery]

I've never heard of a stock engine blowing a rod due to pre-ignition. A AA blown, fuel dragster cranking 12,000RPM maybe..... a stock engine..... I don't think so.

 

My guess is, the tech put something together wrong when changing the cam. Somehing came undone, the piston hit a valve and bent it, next trip up with the piston, it hit the bent valve and all hell broke loose.

 

Heck yes a broken valve will break a rod....... steel doesn't compress very easily and somethings gotta give when that piston comes up and hits it. Especially if the driver has his foot in it (which he has every right to do).

 

I was a GM Service Rep before I was a Dealership Service Manager. The Service Reps job is to protect GM. He is not out to "Get" the customer and he's not looking for excuses to deny a warranty claim. Abuse would have to be so obvious as to be easily provable in a court of law before any Service Rep would even consider denying a claim like this. His 1st objective is to keep GM out of court. If he has to bend the rules in the customer's favor to avoid litigation, he will do so. If a Factory Rep denies this claim, I will be truly shocked. There would have to be a glaring reason to do so.

 

We once had a case where a customer poured water into a revving engine and demolished it. We had a neighbor testify in court that he saw the guy doing it. GM lost the case. Not only did we have to give the guy his $ back on the vehicle, we had to pay all court and attorney costs and we got a world of bad press over it. The only reason that we took it to court was because it was a slam dunk.......

too much timing from a custom tune can hurt rods

 

How?

 

 

Too much of the burn cycle will be complete before the piston reaches TDC therefore the connecting rod will be exposed to extreme pressure as the crank continues to move the piston upwards. The burn cycle is supposed to work with the momentum of the crankshaft. If the fuel mixture is ignited too early it will fight the momentum of the crankshaft. The weakest link between the crankshaft and piston is often the rod and sometimes the wrist pin. The explosion can be compressed to an extent, but the connecting rod and wrist pin are not strong enough to compress the explosion created beyond a certain amount of fuel. The time it takes from the point the spark plug sparks and a certain % of the fuel mixture is burned is set by the ignition timing. Ideally you want maximum cylinder pressure to be achieved right as the piston reaches TDC or cycles slight past TDC. This way the piston is propelled downward with as much force as possible creating effecient HP. If the timing is too early, too much of the fuel mixture is burned before the piston reaches TDC. You have to visualize the fuel catching on fire and understand that it does not just combust in a uniform manner. The flame usually starts at the spark plug and spreads throughout the combustion chamber. We are talking milliseconds but the fire spreads, it does not just appear.

 

[kdixer]

Not saying it is common, but that is how drastically advanced ignition timing could affect the bottom end of the engine. Simply stating the mechanics of it.

 

In this case I think the intent of the dealer was shown by the "we saw signs you over revved your enigine" statement. I would have to know how they "think" they can tell. Maybe what they saw were signs that the piston was attempting to sieze up in the cylinder due to some sort of defect preventing proper lubrication to that particular cylinder?

 

Possibilities are endless without photos or first hand knowledge.

[The Chosen One]

Not saying it is common, but that is how drastically advanced ignition timing could affect the bottom end of the engine. Simply stating the mechanics of it.

 

In this case I think the intent of the dealer was shown by the "we saw signs you over revved your enigine" statement. I would have to know how they "think" they can tell. Maybe what they saw were signs that the piston was attempting to sieze up in the cylinder due to some sort of defect preventing proper lubrication to that particular cylinder?

 

Possibilities are endless without photos or first hand knowledge.

 

 

they had just done an oil change on the truck. it was necessary when taking the top end apart. trust me , this truck is babied she has a lot of highway miles sitting at 72K currently.

[Wires]

Not saying it is common, but that is how drastically advanced ignition timing could affect the bottom end of the engine. Simply stating the mechanics of it.

 

In this case I think the intent of the dealer was shown by the "we saw signs you over revved your enigine" statement. I would have to know how they "think" they can tell. Maybe what they saw were signs that the piston was attempting to sieze up in the cylinder due to some sort of defect preventing proper lubrication to that particular cylinder?

 

Possibilities are endless without photos or first hand knowledge.

 

No way that could happen without the knock sensor detecting and rolling back the timing. If I put 87 octane in my 91 octane truck, it detects knock before my ears can, and retards timing.

 

I don't disagree with what you're saying, it could happen on a non-modern, non-EFI vehicle, but anything with a knock sensor will prevent you from even hearing a "tick", so there is no way it will knock.

[Doug_Scott]

too much timing from a custom tune can hurt rods

 

How?

 

 

Too much of the burn cycle will be complete before the piston reaches TDC therefore the connecting rod will be exposed to extreme pressure as the crank continues to move the piston upwards. The burn cycle is supposed to work with the momentum of the crankshaft. If the fuel mixture is ignited too early it will fight the momentum of the crankshaft. The weakest link between the crankshaft and piston is often the rod and sometimes the wrist pin. The explosion can be compressed to an extent, but the connecting rod and wrist pin are not strong enough to compress the explosion created beyond a certain amount of fuel. The time it takes from the point the spark plug sparks and a certain % of the fuel mixture is burned is set by the ignition timing. Ideally you want maximum cylinder pressure to be achieved right as the piston reaches TDC or cycles slight past TDC. This way the piston is propelled downward with as much force as possible creating effecient HP. If the timing is too early, too much of the fuel mixture is burned before the piston reaches TDC. You have to visualize the fuel catching on fire and understand that it does not just combust in a uniform manner. The flame usually starts at the spark plug and spreads throughout the combustion chamber. We are talking milliseconds but the fire spreads, it does not just appear.

 

 

You are forgetting the knock sensor. If you have the timing so far advanced as to create detonaton (and that is exactly what you are describing), the knock sensor takes over long before that happens and backs the timing up. In other words, you cannot create the scenario you present on an engine with a knock sensor installed and working (and remember, the lack of a knock sensor will set the CEL).

[redvett]

The PCM only retards the timing around 11 deg when knock occurs and if timing is advanced above the threshold spark knock will still occur.

[kdixer]

too much timing from a custom tune can hurt rods

 

How?

 

 

Too much of the burn cycle will be complete before the piston reaches TDC therefore the connecting rod will be exposed to extreme pressure as the crank continues to move the piston upwards. The burn cycle is supposed to work with the momentum of the crankshaft. If the fuel mixture is ignited too early it will fight the momentum of the crankshaft. The weakest link between the crankshaft and piston is often the rod and sometimes the wrist pin. The explosion can be compressed to an extent, but the connecting rod and wrist pin are not strong enough to compress the explosion created beyond a certain amount of fuel. The time it takes from the point the spark plug sparks and a certain % of the fuel mixture is burned is set by the ignition timing. Ideally you want maximum cylinder pressure to be achieved right as the piston reaches TDC or cycles slight past TDC. This way the piston is propelled downward with as much force as possible creating effecient HP. If the timing is too early, too much of the fuel mixture is burned before the piston reaches TDC. You have to visualize the fuel catching on fire and understand that it does not just combust in a uniform manner. The flame usually starts at the spark plug and spreads throughout the combustion chamber. We are talking milliseconds but the fire spreads, it does not just appear.

 

 

You are forgetting the knock sensor. If you have the timing so far advanced as to create detonaton (and that is exactly what you are describing), the knock sensor takes over long before that happens and backs the timing up. In other words, you cannot create the scenario you present on an engine with a knock sensor installed and working (and remember, the lack of a knock sensor will set the CEL).

 

 

Knock sensors help to reduce this scenario, but you cannot rely on knock sensors alone. Detonation has to occur before the knock sensors take action. Or atleast some type of harmonics similar to spark knock. Imediately going to full throttle often sets off the knock sensor. It is often set off during a shift sequence as well. But back to the point, repeated exposure to detonation can be bad even if it is not constant exposure. A person cannot just jack the ignition timing way up and count on the knock sensors to remedy the situation. Not to mention that a tune can also change the function of the knock sensor by changing the amount of timing that is pulled when spark knock is detected. If the timing is advanced enough, the ECM may not pull enough timing to squash the spark knock. I am not saying this is what happened, I am merely saying that is how too much ignition advance can hurt connecting rods which is what you asked.

 

There is another thread in the fuel economy section where the OP (not this topics OP) stated his spark plugs showed signs of detonation. According to your theory, should'nt the knock sensors have prevented that?

[441G]

i think a while back i read on the gm fullsize forums that the op was having some problems with pinging after his custom tune - thats why i posted about the possibilty of what bent the rods

[svensk]

GM had a completely bullet proof setup with the LM7 and then they added AFM and completely turned the 5.3 into a POS. At least you have some really nice high flowing heads on the new 5.3.

After your power-train warranty is up I would switch to LS7 lifters and shut off AFM.

[fbachman]

FYI,

 

Pretty sure they can pull the maximum revs from the PCM, so in 15 seconds they can tell you what the maxium it was rev'd too.

 

I believe that belongs in the OBDII standard. I know Acura could do that with their PCM's. They told me I hit 7.5k in 1st gear @ 65MPH (missed a shift....)

 

Sounds like they're trying to screw you over.

 

This is a good point. There are many scan tools out there that allow you to pull the logs and save the data yourself. Not saying their cheap.... but may be worth pulling the data yourself.... incase they claim something that may not be supported by the data you have.

[kad2112]

What was the result? Did this get covered under warranty?

Thanks

Keith

[nickvrebel]

No way that could happen without the knock sensor detecting and rolling back the timing. If I put 87 octane in my 91 octane truck, it detects knock before my ears can, and retards timing.

 

I don't disagree with what you're saying, it could happen on a non-modern, non-EFI vehicle, but anything with a knock sensor will prevent you from even hearing a "tick", so there is no way it will knock.

want to bet?

 

You are forgetting the knock sensor. If you have the timing so far advanced as to create detonaton (and that is exactly what you are describing), the knock sensor takes over long before that happens and backs the timing up. In other words, you cannot create the scenario you present on an engine with a knock sensor installed and working (and remember, the lack of a knock sensor will set the CEL).

wait for it.......

 

 

The PCM only retards the timing around 11 deg when knock occurs and if timing is advanced above the threshold spark knock will still occur.

BINGO! and lets not forget, we redvett is commenting on a stock truck. a custom tuned truck could be set at anything. There is a LOT more parameters than simple timing, shift point and speed limiters that a real custom tuner deals with. If you would like to argue otherwise I will gladly load a tune in your truck that will grenade the engine in minutes if you really want... people are saying it can't happen, so it won't hurt anything, right?

[Sly]

Did the truck get covered or not?