Topline pistons cracked, what causes this?

[infinite_kaos]

So I rebuilt my engine a couple months ago, I did a budget rebuild since I needed to get the car running asap. I rebuilt it correctly, with help from the haynes manual and a friend at work (mainly for advice, he didn't touch the engine)

Before I even got to a thousand miles on the engine it blew. For a while it was running good, but couldn't get it to run perfect. I had a gm maf blowthrough set up, and couldn't tune the translator for the life of me, so I never went WOT and I kept it below 4000 rpm below 500 miles. Then slowly took it up to about 6k rpm after the first 500.

When I finally got rid of the translator and blowthrough, I went with a 2g maf and evo 9 injectors with evo 9 fuel pump. I've read on here that, the 560's are enough to compensate for the airflow difference with the 2g maf.

Anyway, a week before the engine blew, I started to get some smoke when I would let off the throttle and it was getting in the cabin and smelled terrible. Not like regular oil, I made a thread about it, but no one said what the smell could be, just gave advice on the smoking.

I disabled the pcv system and the smoke went away. One night driving home, I noticed a very large loss in power and it scared me a little bit. The next day I checked everything, timing, plugs, compression and everything was good to go. Compression was 150 on all 4 cylinders.

I drove to work that day, and right when I was a mile from work, the coolant temp gauge shot to HOT, I immediately shut off the engine, and coasted in neutral until the car came to a stop. Let it cool down, tried to start it and it sounded as if there was no compression whatsoever. I tried starting it again while giving it gas and it started, but it wasn't happy. I limped the car home (with my girlfriend following) and it was running so weak, as if it was on 2 cylinders. Everytime I stopped I had to hold the idle high or it would stall, and when I would start to drive again, smoke would billow out the exhaust.

Got home did a compression test, and got 20's and 30's, I immediately though head gasket, so I started tearing it apart to find the #2 cylinder had basically melted. The front side of the cylinder was missing a big chunk out of it, but it didn't look broken off, it was more like it melted, like the shape of a waterfall (ill post pics later)

I was pissed, I never got any knocking or pinging or anything, and never went WOT. So I pulled the engine out (by hand and by myself, which I don't recomment cause its heavy and my back still hurts ) I tore the engine completely down and I found that every piston was cracked in between the 1st and 2nd ring, and one piston was cracked between the 1st and second ring, and 2nd and third ring. And they were all cracked in two places, like I could pull the chunk out of each cylinder.

So my question is, what would cause this? Is it faulty pistons, or was it operator error. Sorry for the long post, just trying to be as informative as possible.

 

[donniekak]

Your tuning caused the engine to run really lean, and this is the result. Many people have used topline pistons with good results, running super lean will melt any piston. Changing injectors and maf to tune a car is not acceptable. The minimum need to tune is a fuel controller of some sort, and most important, a way to see the afr. Even a logger with a narrowband voltage reading is better than nothing.

 

[Jeff99GS]

Man you ran her lean

You gotta post some pics of these things

 

[brian9397gsx]

she went lean i also had toplines fail but it was due to detonation cracked 2 of them was not their fault

 

[GSX93DSM]

I wouldn't really say you go it to run lean. The fact that it got that hot probably blew a gasket and possibly cracked the pistons. Second getting rid of the pcv system is bad; especiallyif it is not done right. That can blow crankcase seals causing problems. As for running lean. If the only thing you had was blow through and maf, with stock injectors and fuel pump or even if you had bigger injectors and a fuel pump it would run more rich. You would set the maf to see size injectors you got and be done. Running lean is kind of hard for me to believe, for what you have got.

 

[schemauer]

Running lean melted the pistons. Common result. Cracked piston or ring land is usually detonation related. With an untuned engine who knows what was going on inside that thing.

 

[infinite_kaos]

I guess its possible to have run it lean although I can say that I monitored what I could to prevent that. I had the gen 2 translator and was able to see my o2 voltage, when I would get the voltage around .98 it would stutter and bog out in higher rpms, so I would go negative in the mainscale until the stuttering and boffing stopped, but the o2 voltage was showing zero's! So I figured faulty o2.

The time that anything bad happened was on the long trip that it started smoking in the cabin everytime I built boost then let off the throttle.

The pcv elimination was a temp fix to see if the pcv valve was the cause of the smoke. When I removed it and tried to blowthrough one side I couldn't the other side I could, but I figured under I pressure then I can blow air was getting passed it. And it proved to be correct when the smoking stopped.

I have read the pros and cons of removing the pcv and didn't think it would result to a blow motor, as a matter of fact, the info I read stated you get better crank ventilation under boost with two breathers as opposed to one, since the pcv closes under positive pressure from the manifold.

When I finally got rid of the gm maf setup and translator and went with the 2g maf, the car ran better, but it was still lagging. I believe the detonation occured during the time the gm maf was installed and finally the engine gave out the day that I drove to work. Could that be a possibility?

 

[bastard dsm]

thats what happens when you dont do it right.

 

[lacroixdp]

If you can't afford the proper monitoring equipment, you are better off leaving the 1G MAF and 450cc injectors on. As you found out, it is very risky to modify your car without some sort of logging solution and a way to either check your EGT or your A/F. If you would have had either one of those, they would have warned you a long time ago of impending doom. IMHO, it is the very first thing you should buy - do it before you touch anything else in that engine bay. A logger should be right after that, if not at the same time. The PCV modification didn't blow your engine, but you need to leave it stock. The PCV valve closes under boost to prevent pressurized air from going into your crankcase. I've known more than a few people that go with the 2G MAF and the bigger injectors to compensate, but I do not like that at all... you need at a minimum an SAFC to properly trim your fuel. Hopefully on your next build you'll have better luck.

 

[infinite_kaos]

I agree with what you're saying, I should have definitely had the correct monitoring equipment, and I kick myself in the nuts for not doing it. I knew I should have but thought it would be safe. Especially since I've read that many have had success with the 2g maf and 560 injectors.

But like I have said, I really don't think that's when the problem occured, I think it was from the maft, I had the mainscale at -33 just to get the car to act right.

All in all I've learned from my stupid mistake, this next build will be done right with the correct monitoring and tiuning equipment (ecmlink)

So end result is, the pistons cracked because I'm stupid . But this just gives me a reason to do it right. I'm gonna take my time, and not use this car as a DD (obviously ) and get another car in the mean time so I don't rush things.

Thanks for being blunt guys, I honestly appreciate it.

 

[TOONAH]

Since you said that all four pistons were cracked between rings, I will agree with the others
that detonation, aka, ping, knock etc most likely did the damage. It is also possible however, that you got the number one and number two rings bass ackwards during install.
Another cause of this type of failure is improper ring gap.
Did you gap the rings to factory specs?.
Getting back to 'knock' damage though. Turbo 4G63's have a knock sensor and the ECM is supposed to retard the timing if a certain knock threshold is reached. So I might ask if you had the base timing set right. On initial start up, one usually uses a timing light to check base timing immediately.
I do also agree on the good advice given in this thread that any mods involving air and fuel must be accompanied by a Stoich gauge (air/fuel ratio). It is more important than a data logger system. A narrow band gauge can be had for $50 and since this type of gauge has very high input impedance in can be wired in parallel to the ecm signal.
Good luck on your re-rebuild!
Check those ring gaps near the top, in the middle and the bottom of the cylinders. If you see a variance of greater than four thousandths, have the block bored and honed.

 

[infinite_kaos]

I rebuilt the engine to factory specs, rings gapped properly, checked, double checked, triple checked everything, correct placement of rings, correct placement of ring gaps around the piston. Every part of the rebuild was done by the book.

I think it was just the matter of running too lean. Like I said learned from my mistake, and will be sure to have everything that I need.

 

[TOONAH]

Well, hope my Mahle pistons don't melt down! I just got the motor running after a complete rebuild and now need to fine tune it. I don't even have an o2 sensor in it so it is running really rich. I need a wideband controller with a Stoich gauge for starters. Since I will be using a 3" GM MAF, I guess I need a MAFT Pro too. Thats $600 more. Jeez, my project is breaking the bank. I can tell the motor is going to pull like a monster. I don't intend to rev it over 3K rpm till I have the above gear installed and check for boost leaks.
The MAFT Pro is supposed to let me do my own fuel maps.

 

[BogusSVO]

the way you discribed your pistons failing, is common when the ring end gap is not correct.
You said you "built it by the book", thats good if EVERYTHING is going back stock, but when you mod, thats when other things have to be changed.
The ring end gap you run on a 10 psi engine, is not going to be the same as you run on a 25psi engine.

What happened was your cylinder temps got higher than stock, and the rings grew, closing up all the end gap, once that happened, the rings "waved" in the ring land, placing a higer side loads on the ring lands causing them to snap. Something had to give.

I personally do not belielve in cast/hyper pistons in a forced inducted engine. Forged is always better. Yes I know there are some here that run them with out issues, but I would have to bet they have all the monitering bells and whisles, and can tune, and have spent hours and hours, working the boost and tune up to the higer boost ranges. I do give those guys Kudos for that.

But for the guys who do not have a grand in montering/tuning equipment, Get forged pistons or run lower boost levels.

when you rebuild, check your ring end gap closely, if you go with stock replacement rings again, I would advise you to add .003-.005 MORE ring end gap than max stock spec if you plan on running more than stock boost.
If you get aftermarket rings, read the paper that is included, most of the big ring makers will include a chart with a formula to give you the ring end gap. most of the time they will give you a factor to multiply by your bore size to give ring end gap.

here is an example of what I am talking about
the ring maker, Total seal Piston rings, Gapless top ring set
blown gas top ring Boxe X.007= ring gap
2nd ring BoxeX.006= ring gap

I still add about .003 to this just to feel a little safer.

so an 85mm bore x .03937 =3.346 converting form mm to inch
3.346x .007=.023 ring end gap top ring
3.346x .006= .020 ring end gap 2nd ring