crvtec90 Posted January 9, 2009 Report Share Posted January 9, 2009 I bought a rebuilt motor in order to save time and I am lucky that I did not install it. I dropped the pan first to get a good look before wasting time putting in a bad engine. Two of the piston skirts had pieces broke off the bottom and another was cracked and would probably break soon. What makes this happen.? The engine had new bearings but i am not sure if it had new rings. What would make this happen? I know the motor was run after the build due to the carbon in the cylinders but I dont know what turbo or possible mods. When I took the rod cap off one the pistons, it fell out on its own ..... so I believe there would have been very low compression on that cylinder. Sorry if this is in the wrong forum. Link to comment Share on other sites More sharing options...
Technology Posted January 9, 2009 Report Share Posted January 9, 2009 Yeah, the piston would normally stay in there, even if it was super oily. Were the rings broken? The other option is that the piston was the wrong size for the engine. Link to comment Share on other sites More sharing options...
Tim_C. Posted January 9, 2009 Report Share Posted January 9, 2009 Detonation. It makes the piston pivot on the pin hard and quick and it flexes the rings, puts a lot of stress on the ring lands, and smacks the skirt on the cylinder wall. Link to comment Share on other sites More sharing options...
Indiana Posted January 9, 2009 Report Share Posted January 9, 2009 I've never seen a piston with a cracked skirt lets see some pictures. Just because a rod cap fell off means nothing and you can't assume compression at all just because you see a cracked skirt you'd have to see the rings to know and the rest of the piston. I'll guess that by now you have those all removed and have looked at them. What did you find and I hope you didn't pay much for that. Link to comment Share on other sites More sharing options...
TurboRaider Posted January 9, 2009 Report Share Posted January 9, 2009 Skirt cracking is common on some motors. The factory used a solid skirt piston possibly because they had problems with isolated skirts that are used on the NA motors If someone replaced the factory pistons with one that have a slot throught the oil groove ( isolated skirt) its not surprising they would crack. Curious to see what kind of pistons you have. Kevin Link to comment Share on other sites More sharing options...
Dad Posted January 9, 2009 Report Share Posted January 9, 2009 Too much piston to wall clearance perhaps? Dad Link to comment Share on other sites More sharing options...
Indiana Posted January 9, 2009 Report Share Posted January 9, 2009 (edited) Skirt cracking is common on some motors. The factory used a solid skirt piston possibly because they had problems with isolated skirts that are used on the NA motors If someone replaced the factory pistons with one that have a slot throught the oil groove ( isolated skirt) its not surprising they would crack. Curious to see what kind of pistons you have. KevinI wonder if this engine he got has dished pistons and oil jets he didn't say maybe he isn't aware of those differences. Early pistons were like this and somewhere, maybe it was the 2.0 turbo motor eaerly to mid 80s I'm pretty sure Mitsubishi did that then they changed all of them at the same time. These are ACL, AU parts. AU had a Mitsubishi engine plant that recently closed. http://www.b2600turbo.com/images/IM000364.JPG http://www.b2600turbo.com/images/IM000366.JPG Your motor you bought, do the pistons have a dish in the top and you see oil jets in the block? http://www.b2600turbo.com/images/IM000182.JPG http://www.b2600turbo.com/images/IM000256.JPG Edited January 9, 2009 by Indiana Link to comment Share on other sites More sharing options...
crvtec90 Posted January 9, 2009 Author Report Share Posted January 9, 2009 U guys are great! Thanx 4 all the replies. This whole experience has been very upsetting, but i cant say I have not been warned. There are more than a few threads on these engines being put together without paying close attention to the details. I was shocked to see a rebuilt engine that did not get new freeze plugs. They are cheap and easy to install. One of the freeze plugs looked like someone gooped some epoxy on it to stop a leak. I took my pocket screwdriver and poked at another one that looked funky and it put a hole in it. Whoever installed the head must have had trouble getting the cam gear to line up because there were deep scratches and gouges in the end of the cam made by using pliers to hold it. Some lifters were pitted and the gasket surface of the head was pitted. There were deep circles under the head bolts like there was no oil used when tightened down and I could see where the head was hit a few times when hammering in the jet valve eliminator plugs. All this added up to loose metal in the engine which made some nice grooves in the cam. I spent the money I should have used to build it myself and now i need to spend more. I did get a decent crank,rods,bearings, arp head studs out of it but it was not what i really needed. Anyway, I dug the pistons out and they are not oem. I noticed a few of the rings are very tight like the ring lands are crushed and the spacing of the gaps is not correct either. Link to comment Share on other sites More sharing options...
Indiana Posted January 9, 2009 Report Share Posted January 9, 2009 (edited) I don't see marking that would indicate they are oversize but that motor was burning oil and that motor has 1000s of miles on it from the way those ring lands have burnt oil like that. The marks in the head are likely from when the motor died in the first place from a broken chain that killed the oil pump and the head was chewed up and they reused it. That skirt may just have been damaged if dropped before installation. How is the honing marks in the cylinders? Are they all smoothed off and look shiney? Maybe those were ten over pistons put in a stock bore cylinder. That motor could have been rebuilt ten years ago who knows. Edited January 9, 2009 by Indiana Link to comment Share on other sites More sharing options...
crvtec90 Posted January 9, 2009 Author Report Share Posted January 9, 2009 Indiana, thanx 4 the piston pics. U and TurboRaider are correct. yes mine do have the slot in the oil ring groove. I do have the piston oil squirters though. The rods are factory but they are not the same. 2 have a D, 1 is an I , and 1 F . The rod cap did not fall out . The piston itself slid out when i took the cap loose. The motor was on the stand upside down and it just fell to the bottom. Only one piston did this. Link to comment Share on other sites More sharing options...
Edde Posted January 9, 2009 Report Share Posted January 9, 2009 Yikes, what a mess. You didn't get that motor from someone here I hope. Link to comment Share on other sites More sharing options...
crvtec90 Posted January 9, 2009 Author Report Share Posted January 9, 2009 Yikes, what a mess. You didn't get that motor from someone here I hope. Yes i did. I tried to get a partial refund with no luck. Shot me down saying he had too much money invested to let go for cheaper. Link to comment Share on other sites More sharing options...
Dcrasta Posted January 9, 2009 Report Share Posted January 9, 2009 (edited) Feedback forum Name and Shame. Thats a sad motor. Can the block be saved/rebuilt? You can go cheap with some factory cast pistons. Edited January 9, 2009 by Dcrasta Link to comment Share on other sites More sharing options...
TurboRaider Posted January 10, 2009 Report Share Posted January 10, 2009 (edited) Most cracked piston skirt I have seen cracked through the oil ring groove. Cracks at the bottom? Wtw... I agree with Indianna that might be from the piston hitting the rod on assembly. A long time ago I had a turbo motor with Sealed Power pistons and the slot in the ring groove. The motor was great till it hit about 60,000 miles and then it got loud. All the pistons skirts had cracked through the ring groove. High loads and high RPM on a long stroke motor are a bad match for that style of piston. Als the sharper the notch at the end of the groove the sooner it will fail. I would love to see a good high res picture of the cracked section. Kevin Edited January 10, 2009 by TurboRaider Link to comment Share on other sites More sharing options...
crvtec90 Posted January 10, 2009 Author Report Share Posted January 10, 2009 The cracked pistons did not treat the block fairly. The cylinders have scoring. I glanced at it earlier and I dont see crosshatch. Definitely needs oversize pistons and boring. I have my original block still and it looks good. I can still see the crosshatch and the factory pistons are not beat up. I had cracked the head on my original engine and figured it would be better to just swap the whole thing and not have to worry about the bottom end. Now I think i will just find a cheap head and use my original shorblock. There was 80-90K on it . The crank and main bearings are nice and clean. The rod bearings have dark areas but are smooth. I thought there was a service bulletin about replacing the rod bearings at the dealer. Does coolant in the oil make them dark. Maybe give it a quick hone and new rings, or should I just clean it up, put it back together and run it. I dont have the block here 4 pics right now. Just wanna drive it again soon. Then use the beat up block to do the proper rebuild to support future mods. Link to comment Share on other sites More sharing options...
crvtec90 Posted January 10, 2009 Author Report Share Posted January 10, 2009 (edited) heres a pic of another piston that was cracked but not broken loose yet. My camera is not super and neither are my photo skills. hope this comes out. left side of the skirt cracked 1/3 of the way down. Edited January 10, 2009 by crvtec90 Link to comment Share on other sites More sharing options...
Indiana Posted January 10, 2009 Report Share Posted January 10, 2009 (edited) I have a thought, OEM pistons and most aftermarket are all offset pins for this motor but the mfg. puts a mark on the top so you know which is to go to the front. JE for example doesn't bother to put a mark on theirs because they do not have an offset pin so a mark wouldn't matter. If I had to guess I'd say those pistons were put in all backwards if the mark was misread or the machine shop put them on the rods backwards and then someone looked at the rods to know which was the front so I'd look in to that and then knock some heads for sure if that was the case. I have seen this from a DSM we got with one of those wonderful JDM crap junkyard engines in it people buy and think they are still good. Just for the sake of building that motor and wondering why it didn't seem to run properly we did pull it out and guess what? All the pistons were in backwards. The honing marks were all worn off and the skirts were smooth. One rod had been replaced and when the machine shop measured it it was too small and that was not all that bad but who ever had that motor in JAPAN frucked it up cause the guy we got it from all he did was buy it and install it, it had that cyclone intake manifold with the duel runners and not the parts to make it work and it would never run right and that's the way I bought it. The "JDM" motor was junk there are morons over there too. and ask that one guy if this post is thread jacking Edited January 10, 2009 by Indiana Link to comment Share on other sites More sharing options...
TurboRaider Posted January 10, 2009 Report Share Posted January 10, 2009 (edited) One last thought is that pistons are typicly turned to have a barrel shape to them and the peak of the barrel is typicly at the center of the skirt and that is where the load should be taken and where you would see most polishing. I could not see that in the photos. It might be that the pistons were overheated and the skirts colapsed. I also remember seeing some ACL pistons that fit pretty tight at the bottom of the skirt. Also the deep circles under the head bolts can happen from lots of thermal cycles over time or a really good overheat the pulls the washers into the head as the head expands and the loads go through the roof. Aslo from the picture it almost looks like the tip of the skirt is broken outwards, is that right? Can you get a close up of the wear marks around the crack? The highest load area should be super polished. Wierd stuff..... Kevin Edited January 10, 2009 by TurboRaider Link to comment Share on other sites More sharing options...
crvtec90 Posted January 11, 2009 Author Report Share Posted January 11, 2009 The pistons do have arrows on top to point forward and If i remember correctly they were. However I thought the rods were supposed to be facing a certain way, not sure which way, or am I wrong. If I can borrow my co-workers camera I can get some better pics. The ring lands are definitely crushed a little because the rings dont move easily on any of the pistons. Link to comment Share on other sites More sharing options...
benja92231 Posted January 17, 2009 Report Share Posted January 17, 2009 I agree with Dad,ask the guy that sold you the motor if he took it to a machine shop or if he has bills for machine work? Link to comment Share on other sites More sharing options...
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