CR melted piston discussion, why, why not, and for the love of god how not to..

OK I have to make a post before I go to bed while it's on my mind... Picture this, because I still don't think many of you get what I'm trying to say, and I apologize... A mechanical engine usually melts pistons due to a faulty/ cracked injector tip.. Why does this melt pistons? Raw fuel pools in the combustion bowl and when ignited, a extreme hot spot is created and the piston might as well be in a forge.. So if you have increased rail pressure and a pilot injection event that has been altered to occur sooner, more fuel than needed is injected too early and causes raw fuel to pool in the combustion bowl. When this is ignited by the next occurring event and the piston might as well be in a forge... please share your opinions, but this is what i see...
 
Devan Manis said:
I don't think that is the case. The common rails are quieter for the simple fact that the cylinder pressure curves are more linear and less spikey. The multiple injection events help to smooth out the cylinder pressure curve. The injection events of the 12v would be more linear, but one all the fuel in the cylinder combusts the pressure spike is out of controll which causes the rattle.
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your right on the pressure curves being more linier in cr's due to the events, but with the mutiple injection events the temps should be sustained for a longer period of time than in the 12v. that crazy pressure spike on the 12v should be around where the highest cyl temps are, and it should drop from there as the pressure dies off, whereas in the cr that temp range would be more linier as its being sustand by the multiple events therfor exposing the piston to higher temps for a longer period of time and reducing the ability of the piston to absorb the heat before it becomes to much right? cause if the same amount of fuel was injected in each engine, the cr piston should be exposed to high temps for slightly longer right?
 
XTrEmE9156 said:
OK I have to make a post before I go to bed while it's on my mind... Picture this, because I still don't think many of you get what I'm trying to say, and I apologize... A mechanical engine usually melts pistons due to a faulty/ cracked injector tip.. Why does this melt pistons? Raw fuel pools in the combustion bowl and when ignited, a extreme hot spot is created and the piston might as well be in a forge.. So if you have increased rail pressure and a pilot injection event that has been altered to occur sooner, more fuel than needed is injected too early and causes raw fuel to pool in the combustion bowl. When this is ignited by the next occurring event and the piston might as well be in a forge... please share your opinions, but this is what i see...
Click to expand...

i think you are spot on on this one. cause the same thing happens in cr's if the tip leaks, you lose a piston due to raw fuel burning on the piston. that first injection event could act exactly like that if its sprayed in a large enough quantity and sparyed at a time where it doesnt get the chance to burn off proporly ( due to more fuel being injected, at a higher rpm, at an earlier timing point due to mods).



i think its a combo of all of these things weve talked about honestlty
 
One more thing I will add to the discussion on cr injs and rpms. A 600 series engine has 3 injection events. You can make peak power with that engine at around 3200-3400rpms and then it dives off. Now get rid of two events and how much faster is the injector now? How many rpms can that inj now work at and still be effecient now that it cut its work down by more then half?

Has anyone seen the Banks Dmax go down the track? How many events do you think they are running? I will give you a clue, Bosch software does one injection event.
 
and theres a reason for that too.

well look at it from cummins point of veiw, why is that pre event there? to reduce emmitions by raising cyl temps slightly before the main injection events take place so they burn better and cleaner. the other seperate events are there to quiet the engine by reducing pressure spikes cause those are all things your adverage person doesnt want and the gov. doesnt want. these engines are designed for queit, emmitions complient operation, not crazy power output as that can be done with one event, although it will be dirtier
 
bprumos said:
your right on the pressure curves being more linier in cr's due to the events, but with the mutiple injection events the temps should be sustained for a longer period of time than in the 12v. that crazy pressure spike on the 12v should be around where the highest cyl temps are, and it should drop from there as the pressure dies off, whereas in the cr that temp range would be more linier as its being sustand by the multiple events therfor exposing the piston to higher temps for a longer period of time and reducing the ability of the piston to absorb the heat before it becomes to much right? cause if the same amount of fuel was injected in each engine, the cr piston should be exposed to high temps for slightly longer right?
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I think you are spot on with that, but the reason I don't believe that this is the cause of the melt downs is because it doesn't add up in other common rail, non cummins applications.
 
the reason ithink it doesnt add up in the other cr's like dmax is cause of different piston makeup. the dmax pistons should be under almost exatly the same amount of stress as a cr cummins give or take a little, but thier cracking thier pistons instead of melting them, that tells me that their pistons are a harder alloy that probably resists melting more then the cummins ones, but is more prone to cracking like thier doing. the dmax pistons are also quite a bit smaller than the cummins ones so therefore theres less matierial there to handle that same amount of stress which would lead to why they make thier pistons a little harder than the cummins ones.

and i think a big reason you dont really hear of it as much in the other cr aplications is cause the dmax and the cr cummins are the two largest player in the high performance common rail diesel field or whatever you wanna call it. those two engine are really the only two cr diesels of that size that are modded to such an extent
 
With exception of a few, the 03-early 04 don't seem to have the problem as bad as the 04.5-07 do. Check out the thread they started to see what type of cr's melt the most and i'd say its 95% are 04.5 and later. Another reason I don't believe it's related to the efficeincy of the burn. It would make it alot easier for me to make up my mind completely if someone had a cut away of an 03 piston, or even a vp.
 
the reason the later ones melt is becuase all that small pre injection is there for is to pre heat the cyl so that the main events burn better, and the different piston is prolly there to aid in that. the earlier ones are the same setup but without that pre event and a piston designed to operate without one and they dont melt cause thier cyl temps are a few hundred degrees cooler right before the main shots of fuel are spit in.
 
I think you have it backwards, the 03 and up all have a pre-injection event. The 04.5 and later all have an additional third event to help heat up the CAT. The third event is probably injected to late to really burn to the point where the cylinder temps that the crown of the piston see are affected, but are manifest by the higher EGT. I remember when the cummins 600's came out that everyone was reporting really high egt and were concerned over it, but these were a result of the third event.
 
bdp said:
One more thing I will add to the discussion on cr injs and rpms. A 600 series engine has 3 injection events. You can make peak power with that engine at around 3200-3400rpms and then it dives off. Now get rid of two events and how much faster is the injector now? How many rpms can that inj now work at and still be effecient now that it cut its work down by more then half?

Has anyone seen the Banks Dmax go down the track? How many events do you think they are running? I will give you a clue, Bosch software does one injection event.
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What about a D-max? You can turn over 5K and it still have a couple of events.....

HP fall off is programming. It may turn over 4K on a dodge, but there isn't any duration up there.
 
The additional injection events are for emission purposes; pre event for NOx and noise reduction, and post events for cat. heating and/or DPF heating. For strictly performance, I think a single injection would be the most ideal.

I assume the tuning required (ie: tming and pulse width) is something most people do not want to get involved in with the cummins?
 
triton said:
How bout looking at this from another angle. Stock trucks can typically handle sustained periods of heat.... why ? Computer controlled timing, duration and fueling/defueling. We do nothing but increase every one of those parameters with our trucks but, not in a controlled way. If the programming can be done to where events don't over lap either other and work with each other.... we'd be good. Otherwise, by pushing and pushing for more power without controlled programming.... we're going to continue to see melting pistons.

just some random rambling :)
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this makes perfect sence as well.. But has its fault as well...SO if we leave a CR stock it wont melt pistons? not so true if you read some of what is on here... stock CR's have melted pistons,

Unbroken has another good way, incorrect angle, incorrect bowl, and injection pressure way to high...equals the mess we are in right now..

So why do we need to run smaller turbos to keep these things inline? From reading this, it is stated that too clean a burn equals melted pistons? but as merrick said, a higher EGT truck will live? quite contrary to the 12V's..

elimination of pressure boxes will also stop this problem?

so what this, and readin the other 200 posts says..

run a smaller turbo, hotter egts, no pressure box, and your problems are reduced? but not eliminated?

Seems these things are better left stock to "avoid" problems. whats the fun of a stock truck? hence why tow rigs have minor mods only?

So again, what is the threshold on these things? or the so called "safer zone" for CR's? or is there none?

This bein the case, if the 6.7 went back to the previous design, in theory, shouldnt it be a better motor than the 5.9? You lose power due to the emissions stuff, but your motor lives with the reduced risk of a melted piston?

if this is so, its perfect example of you cannot have your cake and eat it too...

someone please correct me if i am wrong...
 
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chrleb1 said:
What about a D-max? You can turn over 5K and it still have a couple of events.....

HP fall off is programming. It may turn over 4K on a dodge, but there isn't any duration up there.
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My point was poeple are saying the inj isnt fast enough for more rpm I say it is. I know the power isnt dropping off due to the multiple events, thats more due to inadequet inj drivers.
 
Well add me to the list of melted piston owners. just got word num 3 looks like a mushroom, injector still looks good. valves hit on num 1.
03
smarty tntR
lev 5
timming 2
rp2
mp8 15% holding 27K all the way down 1/4 with 90hp sticks and a ATS Aurora 5K. My temps were in the 1450 range with eng around 230deg. Truck ran fine, started knocking (valve to piston on num 1) but still ran great. There was no abnormal smoke or vibration. I'll try and get some pics.
 
joelc79 said:
Well add me to the list of melted piston owners. just got word num 3 looks like a mushroom, injector still looks good. valves hit on num 1.
03
smarty tntR
lev 5
timming 2
rp2
mp8 15% holding 27K all the way down 1/4 with 90hp sticks and a ATS Aurora 5K. My temps were in the 1450 range with eng around 230deg. Truck ran fine, started knocking (valve to piston on num 1) but still ran great. There was no abnormal smoke or vibration. I'll try and get some pics.
Click to expand...



Very Sorry to hear that man!!
 
joelc79 said:
Well add me to the list of melted piston owners. just got word num 3 looks like a mushroom, injector still looks good. valves hit on num 1.
03
smarty tntR
lev 5
timming 2
rp2
mp8 15% holding 27K all the way down 1/4 with 90hp sticks and a ATS Aurora 5K. My temps were in the 1450 range with eng around 230deg. Truck ran fine, started knocking (valve to piston on num 1) but still ran great. There was no abnormal smoke or vibration. I'll try and get some pics.
Click to expand...

:bang:doh: Sorry to here buddy
 
See, I still dont get it... For the last 2 years I drag raced and pulled my 06 with 3.3's stg3 cp3 fro John and a 66 and got it super hot multiple times with rp on 4 and the puck on 60hp. You would think that my pistons would have been torched. Ive looked at them several times and all is well. Why is my situation any different then others? Also, Timing has always been on #3 RP was always above 27.5k
 
HIGH TECH RAM said:
See, I still dont get it... For the last 2 years I drag raced and pulled my 06 with 3.3's stg3 cp3 fro John and a 66 and got it super hot multiple times with rp on 4 and the puck on 60hp. You would think that my pistons would have been torched. Ive looked at them several times and all is well. Why is my situation any different then others? Also, Timing has always been on #3 RP was always above 27.5k
Click to expand...

I hope your not superstitious man!!!! Knock on some wood ,Fast!!!!

LOL
 
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