240hoke Posted December 30, 2006 Share Posted December 30, 2006 So today I took out my engine and tore it down. The reason I was tearing it down was to find and mark exact TDC for more accurate tuning and to install some ARP rod bolts. I was also wanting to double check my cam timing as my car had always been kinda hard to start and lately had seemed to be missing a little at idle. Turns out my timing was dead on, but I found something much worse: piston damage mainly concentrated on #6 with a little on #5. It looks like something got inside my motor and bounced around for a little while. Whatever it was it was big enough to damage the motor but small enough to not do any damage whatsoever to the turbo. These are Forged and ceramic coated JE pistons that are less then a year old (Notice the ceramic coating!! .... perfect for turbo/nitrous applications my ASS). Piston Damage: Head Damage: The dimples were enough to pinch the top compression ring so much so I cant remove it with any resonable force. Scoring on the sides: Scoring on hte main bearings So thats where im at right now, I honestly dont know how it happened, but it did. Not exactly sure what to do at this point either. There is no crank or block damage that i can see at all. Another thing wierd I noticed is i can wiggle the pistons a bit in there bores Your thoughts and suggestions please, if yall think this is bad enough to warrant a rebuild i may just be junking the L28 all together. Quote Link to comment Share on other sites More sharing options...
Guest 280ZForce Posted December 30, 2006 Share Posted December 30, 2006 Ouch, looks lil a lil bb was shooting around in there. Sorry to hear the bad news, that majorly sucks...good luck on whatever engine you pursue next. Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted December 30, 2006 Share Posted December 30, 2006 ouch dude!! so what could that have been? How many miles are on the bearings? this is a standard size bearing from my motor that was supposedly an oiling problem(low oil from leaky motor and one big over-rev). Could it have been another casting imperfection that came out of your head? Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted December 30, 2006 Share Posted December 30, 2006 Wait...does your turbo have ball bearings Austin? Quote Link to comment Share on other sites More sharing options...
240hoke Posted December 30, 2006 Author Share Posted December 30, 2006 Nope, just a regular ol t3 center section. Perhaps it got demolished in the combustion chamber or the damage occured at idle while the turbine speed was slow enough to not be damaged. i dunno if this is what was causing my motor is miss a little, it could have been like this since day one for all I know. Those bearing have a good many miles on them, they were in the motor since Ive had the old 260. But I inspected and reinstalled then when i put the new forged pistons in last year and they were perfect. Its been just a couple thousand miles since then. My guess is the pressure from the object caused extra stress on the bearings. I wasnt tearing the motor down because I thought something was wrong i was just double checking stuff really. This surprised me. heres what that coating used to look like LOL: Quote Link to comment Share on other sites More sharing options...
Guest Aguyandaredhead Posted December 30, 2006 Share Posted December 30, 2006 Did you have anything like the rods "Shot Peened"? It could be a piece that was hidden in a nook or cranny that came loose after assembly. Just a thought. Jeff Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted December 30, 2006 Share Posted December 30, 2006 Thats what you call detonation my friend.... Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted December 30, 2006 Share Posted December 30, 2006 Bummer Austin. I am sorry to see the damage. It does look like detonation. The #6 cylinder runs the hottest (furthest from the water pump) and then the #5 is second. As far as the bearings, well, I am not surprised to see the wear if they have been used on more than one motor. Quote Link to comment Share on other sites More sharing options...
Warren Posted December 30, 2006 Share Posted December 30, 2006 Can't agree with you J. The pattern is too symetrical on both the head and the piston. Looks more like FOD (Foreign Object Damage). Something got sucked in and compressed between the piston and the head...notice the edge of the piston is marked too? Quote Link to comment Share on other sites More sharing options...
240hoke Posted December 30, 2006 Author Share Posted December 30, 2006 I agree with warren and have a hard time believing its detonation. Note especially the raised lip around the dimples and the dimples on the edge of the dish. looks more like a "cold" deformation I guess you could say. But i dunno, I was running some pretty crazy advance at SEZ so umm perhaps it was detonation Heres a picture of detonation I found on gooogle: The bearings were in the same motor just the motor was put in a different car with different pistons. There was no shotpeening done, right now im thinking perhaps MIG slag from the I/C pipes. I blew rings lands on #1 before I did anything else on my last rebuilds with stock pistons, seems like 1 and 6 are the quickest to go due to intake design and as you said cooling on 6 Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted December 30, 2006 Share Posted December 30, 2006 Do the dimples on the dish lip match up with the dimples on the head? It seems like they would. Quote Link to comment Share on other sites More sharing options...
Tony D Posted December 30, 2006 Share Posted December 30, 2006 I'm having to agree with FOD, detonation would make something similar, but more looking like a "sponge" as shown in that last photo, and if it's detonating in #6, that severely, you would see similar formations, only less as dramatic in the other chambers as well. I think Austin has it about the bearing damage, the non-compressibility of the object caused an overload on the bearing, and collapsed the oil wedge. It was something hard, & symetrical. I was in a rush once, and lost an intake washer down the intake on my VW Bus, passed through, but to this day it's hanging on monafilament fishing string from the rearview mirror to remind me not to rush. What confounds me is the probability of something that small and round getting in there in the first place. Something like a piece of steel shot that was laying on top of the piston, and occasionally made it up to the rim before blowing out the exhaust valve... All that damage could have happened in cranking the engine initially, and once it fired, out the exhaust it went. Usually this severity of damage would be caused during slow mechanical cranking (like with the starter), as during runnning at even idle speed, the kenetic energy of the parts in contact would start breaking stuff, instead of simply making imprints. That Sucks. Quote Link to comment Share on other sites More sharing options...
blairjj Posted December 30, 2006 Share Posted December 30, 2006 TonyD and Warren, I agree that it was FOD. I look to the scoring on the piston as further proof. Austin are the pistons in #5 and #6 both scored? What about the others? If it was FOD I believe that the object would have increased the sideloading on the piston as well as the bearing. Jay Quote Link to comment Share on other sites More sharing options...
2003z Posted December 30, 2006 Share Posted December 30, 2006 had to be fod, those patterns are just too similar to be anything else. Sorry Austin, whatever the cause, it sucks, but the good thing is you found it now, and not in the middle of nowhere on a cold dark night. Quote Link to comment Share on other sites More sharing options...
240hoke Posted December 30, 2006 Author Share Posted December 30, 2006 Thanks for all the replies guys. Blairjj there is literally one single dimple on #5. Bearing damage is to the top as well. I have only pulled the #6 piston so far, I will check all the other bearings and scoring in the morning. Quote Link to comment Share on other sites More sharing options...
olie05 Posted December 30, 2006 Share Posted December 30, 2006 sounds/looks like a rebore is in order. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted December 30, 2006 Share Posted December 30, 2006 The dimples on the head match the ones on the piston and they only occur where the raised part of the piston came up to the head indicating interference. It definitely looks like it was a BB or a ball bearing. Not detonation. You can probably calculate with some accuracy the sized of the FOD and the number of revolutions that it took to get it out. It came in from one valve and followed the edge of the bore wall, bouncing it's way over to the exhaust valve and out. You were pulling lateral G's at the time which kept it to one side of the bore....hmm. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted December 30, 2006 Share Posted December 30, 2006 im going to guess slag from welding intercooler piping.. that got sucked in or broke loose ... thats what me and bobby concluded lol Quote Link to comment Share on other sites More sharing options...
Dragonfly Posted December 30, 2006 Share Posted December 30, 2006 I agree with the others who say FOD, I also agree with Tony D that it was probably done with the engine being cranked over by the strater and not while running. Any object hard enough to make that many impacts and not be deformed itself in the squish zone (flat part of the head) would have been like the perverbial "bull in a china shop" and done an insane amount of damage at any engine speed above cranking. I would also take a very close look at the valves to see if there is any damage on the back sides or in the runners to indicate how this got into the engine. What confuses me more than the #6 piston is the #5 piston only having a single impact mark??? If you got a piece of something in each of them how did #5 get so lucky by comparison? Myself being the way that I am the amount of damage you have would warrant a rebuild if it were my engine. Good luck and I hope you solve the mystery. Dragonfly Quote Link to comment Share on other sites More sharing options...
Cjarloz Posted December 30, 2006 Share Posted December 30, 2006 dang sorry about the luck austin. look at this as a growing experience. a chance to grow into a 2jzgte hehehehe Quote Link to comment Share on other sites More sharing options...
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