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Cracked Mahle pistons

13K views 80 replies 34 participants last post by  Short Bus 
#1 ·
In cases like this I like to have parts in my hand, but it appears quite a bit of what failed was due to poor assembly and probably poor machine work. You'd have to pull it father apart as in some cases a spun bearing can ruin the block and crank, some times niether and some times just the crank depending on how long it took to spin.

The pistons cracking is fairly normal. The varible spray patter from piston to piston is a sign of injector problems - possible high mileage and just plain worn out. Could be a result of injection timing as well.
Not ganna say who posted this but was just curious what the assembly or workmanship of the machine work has to do with cracked pistons:doh:

Better yet how many cracked Mahle pistons can be accounted for.
Out of all the engines I have seen with replacement Mahle I have only ever seen 2 engines with cracked pistons and they both shared a lot of similarities.
 
#3 ·


Start there... and once you get that resolved you'll notice that these other problems and engines coming back out all the time just seem to fade away and almost completely disappear.

With that going on, I don't care how you put one together, it's not gonna stay that way all that long.
 
#5 ·
It requires around 30 degrees of actual SOI to hit outside the bowl. For instance, at 3000rpm with an injector lag of .7ms, that would require a minimum of just over 42 and a half degrees of advance to accomplish.

I wonder if that was with the programs that run "9" or with the ones running "12" degrees?
 
#13 ·
Not that it will change the burn marks, but keep in mind that piston was cleaned very well with brake clean before the picture was taken...

I will see if I have any pictures of the old motor too, it had no cracking on it.
 
#7 ·
I wish I would have taken some better pics of the pistons on my stock motor when it blew. They had one hell of a star pattern to them. But I didn't know anything about it at the time.
 
#10 ·
Anyone want to post up some pictures of pistons that have had good tuning on them? Or are none of them motors tore apart lol
 
#14 ·
I admit to not knowing anything about this stuff, so can someone tell me what I am looking for in Charles' pic
 
#15 ·
The injector should spray inside the piston bowl for various reasons and when an engine/injection system are designed, the intent is to make sure this takes place. However, if you advance the injection timing, or do anything to alter the piston to injector relationship or the spray angle, you can end up spraying on the face of the piston, potentially causing problems although sometimes not. In general terms, it is not a good thing.

My only point was in the fact that aside from whether or not it's good or bad, just to make it happen the injector has to be spraying somewhere around 30 degrees in advance of TDC. Since the injectors have a latency in the .6 to .7 or so ms range, when running at a common rpm of say 3000, that would require at least 42 and a half degrees of timing to accomplish. Being that I was running 28 degrees of timing making over 600hp, I find it unnecessary for Joe's engine to show evidence of having run 40 or more degrees.

At some point in injection quantity and engine rpm you just can't hit the stock bowl anymore, and it's unavoidable. But this is when running in the 4000ish rpm range.
 
#26 ·
A Lott LOL of Timing - Not really - only half way to the cylinder walls!
Is that the only tunes that have been on that motor? I could be mistaken, but I've heard he had someone else's tunes on their before also.
 
#20 ·
Man I love this site. I am finally starting to understand all this. So Charles what you are saying is when you start getting into the high HP #'s it is pretty uncontrolable to keep the fuel spray pattern in the bowl.

I get it now. Outside bad inside good. Thanks
 
#22 ·
No.

When you start getting into 40+ degrees of timing it's hard to keep the spray in the bowl. At high rpm (higher than 4000) you start getting to the point where timing appropriate for the rpm with a large injection quantity may or may not be staying in the bowl anymore. But for 99.9% of the 7.3 crowd, that's a non-issue.

I get the feeling it was spraying all over the piston face sub 3000rpm in this case.
 
#51 ·
Joe Diesle...This is NOT Daves fault, he did not built this motor
 
#53 ·
I'm lost, are you talking to yourself?
 
#52 ·
I see all you guys talking about timing but who has really checked it. Just because some software on a screen says it's 1 degree does that mean it's true! Injectors can and will do the same thing all by themselves. do any of you check the spray pattern and angles before installing them? Trying to say this or that caused the problem by looking at a picture is a complete waste of time. You need to have all the parts and inspect them before drawing any conclusions as to what may or maynot been the problem. The outcome is the fuel was sprayed outside the bowl, the reason is everyone on here's wild a$$ guess at this point in time!
 
#58 ·
I've done every last thing you just suggested.

What do I win?



And Sun. Jody can manipulate his viewing application all he wants, but it doesn't change what he's viewing, because he's still looking at the same 224kb of hex code everyone else is. The fact that he quotes values like 9 and 12 makes it abundantly clear that nothing of importance has changed with the inception of his wonder template.

Another thing... if you ever add timing and the truck doesn't pick up power, you are way past where you should be.
 
#54 ·
#55 ·
Weird... Thats what my old motors pistons looked like at 130k with DI and Elite tunes on it...
 
#57 ·
Looking at the good vs. the bad, looks like the first ones are just reversed. Smooth on the left and jagged on the right in the good graph, jagged on the left and smooth on the right in the bad graph.
 
#60 ·
Ide like to hear more about Swamps testing Jody's tuning.
 
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