Keith Browning Posted July 10, 2006 Share Posted July 10, 2006 I have read a lot of posts in various forums that a distinct star shaped pattern on the piston heads is indicative of the use of performance enhancing devices. Is there any truth to that statement? /forums/images/%%GRAEMLIN_URL%%/shrug.gif We have a truck in with blown head gaskets on it's SECOND ENGINE. Very clear carbon star on all pistons. This truck is used to deliver travel trailers and is used heavily for towing. It also has a 4" turbo-back exhaust. Quote Link to comment Share on other sites More sharing options...
sparker Posted July 10, 2006 Share Posted July 10, 2006 I too have heard, point-blank, that there is a very distinct star pattern formed on the piston head when any form of aftermarket programmer has been used. What I've been told is this is due to more radical timing and changed pulse widths. I used to have pictures of this, but I'll see if I can find some. If you have a chance FD, would you snap a pic of what you have and post it? Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted July 10, 2006 Author Share Posted July 10, 2006 I just shot a few pics... will have to wait until I get home to upload. Quote Link to comment Share on other sites More sharing options...
Diesel Jay Posted July 10, 2006 Share Posted July 10, 2006 Every DI diesel will display a star pattern -- stock, or not. However, Nav does have engineers who analyze the patterns as part of their failure analysis. Those guys can tell if timing/pressures were altered, or if too much fuel was injected, based upon the placement and shape of the pattern, as well as any damage/melting of the piston. Thus, you'll always find a star pattern. Quote Link to comment Share on other sites More sharing options...
blown99 Posted July 11, 2006 Share Posted July 11, 2006 Every DI diesel will display a star pattern -- stock, or not. However, Nav does have engineers who analyze the patterns as part of their failure analysis. Those guys can tell if timing/pressures were altered, or if too much fuel was injected, based upon the placement and shape of the pattern, as well as any damage/melting of the piston. Thus, you'll always find a star pattern. \\ I agree with you. I almost always see a star pattern when I do a tear down whether it be a navistar, cummins or cat engine. They can range from dots on the piston in a star pattern to lines ranging out from the tip of the semitorital cone on the piston to the dish. Did the customer burn a hole in a piston? Do you have any pictures to put up? Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted July 11, 2006 Author Share Posted July 11, 2006 Actually, I disagree that you will always initially find a pattern because most of the engines I have apart are not well running specimens. In fact, most of the engines I have had apart were so carboned up there was no visible pattern at all. But I will admit that once a light cleaning of the piston crown is performed a spray pattern does become evident. I have only come across anything this distinct once before now and that is why I ask if there is more to it. Take a look. If you think that this is about "normal" for a 6.0L please share your opinions. Like I said, I don't typically pull apart healthy engines. /forums/images/%%GRAEMLIN_URL%%/wink.gif Quote Link to comment Share on other sites More sharing options...
Cetane Posted July 11, 2006 Share Posted July 11, 2006 I have to agree with Diesel Jay as long as the engine has been running fairly well before the teardown. I have disassembled a lot of diesels lately, from 6 cylinders through the newest ITEC and they all had some sort of "star" pattern on the piston. Most of these had gone through pretty substantial testing in either chassis or dyno development. I have to say most werent production fueling or timing but none of them were being torn down because of piston failure. That being said there is a "science" to reading the pattern kind of like reading a spark plug. I dont think you could immediately say a star pattern indicates a tuner but if you were experienced enough you may be able to tell the difference between normal fueling/timing and a engine that has been subjected to modified values. Quote Link to comment Share on other sites More sharing options...
HGM Posted July 11, 2006 Share Posted July 11, 2006 The way it has been explained to me, the injection should(in a perfect world) be contained inside the bowl.. Different loads may contribute to a variation of how intence the patern might be, but as a rule if the star pattern reaches the outer edges of the piston, it is due to a programer changing the PW and timing, and will begin to burn the edge of the piston.. In my opinion, its not clear enough to say "pay me, you added a chip".. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted July 11, 2006 Author Share Posted July 11, 2006 Thanks for the good posts. /forums/images/%%GRAEMLIN_URL%%/thumbup.gif Okay, perhaps we are learning something here. At least I am. My thinking is that the harder an engine is worked the more the pattern will be evident. I did state that this vehicle is constantly towing so it is obviously well loaded most of the time which is in contrast to the many "Texas Cadillacs" we service. I also believe the size of the pattern also has something to say. Though this piston has been cleaned it shows the pattern largely contained within the bowl. This is more in line with what I typically see. The focus of the photo was the fact that the piston was cracked. I thought I had a shot of the entire crown. With a regular flow of engine work now coming in I am going to start taking more photographs of pistons to see what shows up. Submissions are welcome but let's limit it to 6.0L's. Quote Link to comment Share on other sites More sharing options...
sparker Posted July 11, 2006 Share Posted July 11, 2006 again, excellent info guys. what you are all saying makes sense for sure. FD, those are some pretty distinct patterns for sure and extend out pretty far. Quote Link to comment Share on other sites More sharing options...
Diesel Jay Posted July 11, 2006 Share Posted July 11, 2006 Sorry, should have noted that in a properly running direct-injected diesel, the star pattern will always be evident. Quote: The way it has been explained to me, the injection should(in a perfect world) be contained inside the bowl.. Different loads may contribute to a variation of how intence the patern might be, but as a rule if the star pattern reaches the outer edges of the piston, it is due to a programer changing the PW and timing, and will begin to burn the edge of the piston.. In my opinion, its not clear enough to say "pay me, you added a chip".. There was more truth to this in the past. Combustion was never completed contained within the bowl, but it was more so than with current engines. However, with today's retarded timing and the use of EGR, a lot of combustion occurs after TDC. With the piston traveling downward, and the fuel still burning, you're going to see that pattern expand beyond the piston bowl. As an aside, the whole science behind piston bowl shape and design is very indeterminate. There are a lot of theories to describe how fuel gets moved around in the combustion chamber, with spray patterns, swirl, tumble, cone angle, etc. However, it's very rare to find the theories actually supported by the testing data. So, piston bowl design is really more trial & error than anything else. That also means, however, that trying to contain combustion completely with the bowl is akin to capturing lightning in a bottle. If you have no idea as to the optimum shape, size or placement of the bottle, it's just dumb luck should you happen to succeed. /forums/images/%%GRAEMLIN_URL%%/smile.gif - Jay Quote Link to comment Share on other sites More sharing options...
Diesel Jay Posted July 12, 2006 Share Posted July 12, 2006 I ran this by some folks who analyze these sort of things on a daily basis, and they noted that the pattern here indicates the timing is badly retarded. The injector plumes are too big, as if the piston was too far away from the nozzle while injection was occuring. If things were operating normally, you should see more of the pattern contained within the piston bowl, but in this case, it looks like none of that is occuring. - Jay Quote Link to comment Share on other sites More sharing options...
Torqued_Up Posted July 12, 2006 Share Posted July 12, 2006 So if I read this thread right a pattern should be visible but for the most part contained in the bowl? So Doc, how did this truck run and what was wrong with it? The truck w/ the pistons I mean. Quote Link to comment Share on other sites More sharing options...
sparker Posted July 12, 2006 Share Posted July 12, 2006 What I was figuring is with the larger star pattern, the injection started earlier (hence the retarding of the spray) to complete a longer duration for more fuel; and this timing change would've been caused by a chip/programmer. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted July 13, 2006 Author Share Posted July 13, 2006 So Doc, how did this truck run and what was wrong with it? The truck w/ the pistons I mean. The truck ran really well actually but it was losing and expelling coolant. The end result was right side gasket leaked, the EGR cooler leaked and the right head was bad. The flatness measured 0.004" within a 4" line between cylinders 3 & 6 lengthwise. This is the second truck we found with BOTH a head/gasket concern AND a bad EGR cooler! /forums/images/%%GRAEMLIN_URL%%/eek.gif Quote Link to comment Share on other sites More sharing options...
Diesel Jay Posted July 13, 2006 Share Posted July 13, 2006 What I was figuring is with the larger star pattern, the injection started earlier (hence the retarding of the spray) to complete a longer duration for more fuel; and this timing change would've been caused by a chip/programmer. I asked my contacts the same thing. They noted that if the timing was that far advanced, the CP's would have been astronomical, to the point that you'd start seeing melted aluminum on the pistons. - Jay Quote Link to comment Share on other sites More sharing options...
sparker Posted July 14, 2006 Share Posted July 14, 2006 Quote: Originally posted by sparker: What I was figuring is with the larger star pattern, the injection started earlier (hence the retarding of the spray) to complete a longer duration for more fuel; and this timing change would've been caused by a chip/programmer. I asked my contacts the same thing. They noted that if the timing was that far advanced, the CP's would have been astronomical, to the point that you'd start seeing melted aluminum on the pistons. - Jay Don't some of the programmers/chips cause more injections per rotation? Starting more advanced in the cycle with more injections continuing as the cylinder gets farther down in a retarded sense. I believe some of these do this to help control the CPs and still get away with more fuel. I'm not sure about the melted pistons but if the CPs were that high for that long, he'd most likely be going through coolant as well and be in need of some headstuds. Quote Link to comment Share on other sites More sharing options...
Diesel Jay Posted July 14, 2006 Share Posted July 14, 2006 Don't some of the programmers/chips cause more injections per rotation? Starting more advanced in the cycle with more injections continuing as the cylinder gets farther down in a retarded sense. I believe some of these do this to help control the CPs and still get away with more fuel. I'm not sure about the melted pistons but if the CPs were that high for that long, he'd most likely be going through coolant as well and be in need of some headstuds. Nav couldn't even get Pilot Injection [2 injection events] to work reliably at idle, much less at higher RPM's. The physical, moving parts of the G2 HEUI injector are just too hard to control. Some of the aftermarket programmers have re-enabled PI, but I don't know that any have used it above idle speed. That would be playing with some seriously unknown variables. Quote Link to comment Share on other sites More sharing options...
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