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chipped piston same spot second time! is my car a lemon?

G

guimond47

New member
hey guys roughly 3000km ago my front pistons were chipped idk how it happend because i bought it like that to repair the car and drive it my self. i under up throwing a whole new used bottom end with pistons and all into it and put the l67 heads and lim and supercharger on it. turned out great ran like a charm . now last night i put some headers on that same car ( this is roughly 3000km after that rebuild) ran mint for 24 hrs. today i installed my new aero force gauge as well as the 104 AL plugs . went for a ride down my street with new plugs and then BAM started clicking like crazy . i ran a misfire test on my aero force gauge and had 158~ misfires on cylinder 3. soo i knew something was up. pulled that plug out of cyl 3 and the tip of the plug was bend. i knew there for a chipped piston happend. took me and hour to strip the engine and found that nice chipped piston. now my question is why would i chip a piston with headers stock PCM and running on 91 oct and higher. and its the second time it happend! is it possible to have a bad PCM ? i have a spare bottom end so im gonna replace that 1 piston with another one. is there anything else i should do. the heads have no sign of mark on the or dent. im gonna mostlikly get a machinist to check them out tho. but if theres any idea of why it happend twice someone please let me know. its gonna be like the 4th bottom end in the car going on now since the previous owner had same problem..



do i really need new head bolts because i just bought them 3000km's ago and do i have to hone the cylinder before putting another used piston and rings in it?
cylinder has no damage at all ( boy im lucky)
 


Swap the WHOLE bottom end run AC Delco OE spec plugs you dont need anything over that. What were they gapped at? Could be a million factors. IMO Id use the whole bottom end you said you have and go back to OE spec AC Delco plugs!!!
 
that whole bottom end i had was the old blown one im just gonna take the good piston from the old one and slap it in this one. and as for the plugs im gonna be putting a 3.4 pulley soo i need the 104 AL for less knock . these plug are recommended by like everyone on the forum..... and was gapped at 53 thou.
 
Ur taking the block out to get one piston in? Why not swap the entire block? Also don't reuse TTY bolts. Those head bolts are torqued pretty hard and can be used once. Diamond pistons are nice too
 
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well first things first, fix piston. Do you have a tuner or know someone who can tune it? i would add fuel to the center 2 cylinders and a little more to that one in particular.

Also like said there has to be a reason why that cylinder went out again. if your using the same heads, maybe something is wrong there. like said check the injector for that tube. remove it and make sure there isnt anything clogging it. also take a good look at the exhaust spring and valve for that cylinder. maybe something is binding and it isnt traveling all the way. or the push rod is bent? and it isnt opening all the way and closing early. was there any damage on the spark plug? did it look white or black? this will tell you if it is running rich or lean. if lean... you got a fuel issue. if it looks rich then it might be mechanical issue.

you could always move the injector to another cylinder... but it would suck if it blows another piston.


things to do right now once it is back together. run 103 plugs. i know people may object, but you are having possible detonation that is killing the piston. swap to a colder plug at least just for that one cylinder and gap it closer. also make sure to run 93. and deff dont swap to the 3.4 until you figure out what is going wrong.
 
X3 on the fuel issue. I would check the injector for that cylinder while idling. I wouldn't drive the car too much if you're chipping that quick. On a 95 Grand AM GT I had for a little bit, the injectors were fine when cold, but once the engine heated up, one injector would stop pulsating. I checked using a stethoscope on the injector to hear it. Also, running lean would make the car run hot. Is the car running hot?
 
Was the aeroforce picking up any KR? I think it should have. Also check if your knock sensors are plugged.... I discovered the other day that my rear knock sensor cable was unplugged and it wasn't triggering any SES codes.

See if you can get at least a canned tune, it adds more fuel for WOT and addresses oder issues that may cause KR or lean mixtures.
 


Not only make sure the knock sensors are connected, but you may want to pull them and make sure they aren't coated w/ coolant goo. The old Dex is known to coat them making them not perform as well, or at all.

Then be sure to use some thread sealant on them and torque them to the proper spec when installing or once again they will not read knock correctly. IIRC the spec is 14ft/lbs. You will want to verify this.

I would get a new longblock and go from there instead of piecing one back together that has already eaten 2 pistons. There is something wrong. Get a longblock, swap over your intake and accessories and call it good. With having a job right now the last thing you want is a "project car". You need to put something together that will last and actually get you to and from your new job, not leave you stranded w/ a 5 cylinder over and over.

For the cost of new head bolts (since stockers are TTY and not reuseable), HG's, LIM gaskets and various others to keep doing this over and over, you could have already found one for that price. Check craigslist for a good 3800 motor. Series II, Series III doesn't matter.
 
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For sure...just don't get a high compression 3800...or you'll be asking for more trouble without a way to tune.
 
^^good point, blue. forgot about that. Yea, def. no N/A longblocks. Make sure its from an S/C'd car or you will be doing more than chipping a piston w/o a tune, lol... More like picking pieces of it out of the oil pan :D
 
He said no job atm so piecing together is what he has to work with. If you have the time then I say go for it. I would try doing some bench testing of the injectors first. Think I used a 9v battery to test the ones on the grandam. Just listen if the one for that cylinder sounds different than the rest. The clicking on the bad one for the bad injector was faint, hardly sounded like it moved. If anyone has a better battery supply voltage then please chime in.
 


If you can, do an injector balance test. This will tell you if you are having flow issues with the injectors themselves.:th_winking:
 
Thanks guys for the help . I actually went to a local junk yard and took a piston from a supercharged 3800 still in great sshape. And at the same time i pocket it 3 injectors lmao . Ill just slap one of those on there lol . And other than that im putting it back togethor right now lol:)
 
Good luck on rebuild #5. Hope it holds together for you this time around.

but if theres any idea of why it happend twice someone please let me know. its gonna be like the 4th bottom end in the car going on now since the previous owner had same problem..
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If it blows up again then I would seriously consider just getting a longblock and go from there. Best I can figure w/ buying new headbolts for that side, 1 HG, new LIM gaskets, oil, filter, coolant, TB gasket, machine shop charges to check the head, and shipping on the parts you are probabaly right around $260. This is about half of what I would expect to pay for a good L67 longblock.

Since this motor has already taken out the bottom end 4 times in its life there is something seriously amiss whether it be a fuel supply issue, wiring, ECM, etc. I'd say give it a go one more time then just start fresh. I understand you have no job atm which is why I say to replace it now and come out ahead in the end vs. blowing it up again and again. You will end up spending more $$ on it that you don't have right now. I've been down this road before. After I was 2 motors out and $500 in the hole to my Dad I finally just bought a good used motor and called it a day. That car is still running today w/ no issues.

Heck, someone on here may have a known good longblock they could sell to you at a decent price.
 
darkhorizon said:
Tuning is not a big deal!!!!!

If I had a dollar for every time you talked out your ass about "tuning" I would be rich.
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If you seriously think you can run a high compression bottom end with a regualr GTP PCM...it's a wonder we never hear about all those cars you tune...because they are all in pieces.

Seriously, cut out the crap information.
 
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