07 sti blown ringlands on two stock motors. help!
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This is a discussion on 07 sti blown ringlands on two stock motors. help! within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; hey guys, car is driving me nuts. hoping to get some good suggestions from you all. bought stockish (only cobb ...

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    07 sti blown ringlands on two stock motors. help!

    hey guys, car is driving me nuts. hoping to get some good suggestions from you all.

    bought stockish (only cobb intake and cobb stg1 tune) 07 sti and it hasn't run right since the day i bought it three years ago. p0304 code and idling rough within a few months of buying it. subaru replaced cyl 4 piston (cracked ringland) and rings under warranty and also machined the cylinder heads for the first time and said it was fixed. same exact issue manifested two months later. subaru dealer was super shady so i wasn't going back there. was told by a new tuning shop (specialize in subaru builds and tuning) best way to spend my money would be to put a new short block in it instead of refurbishing factory block. sat car for a year (company truck) while i saved up the money for a new block.

    had shop buy brand new subaru short block and install it along with stage 1 exedy and grimmspeed uppipe. paid to have the shop send heads out to be checked by a machine shop (second time heads have been machined). new motor appeared to work fine. after 2000 miles on the brand new short block, had same issue yet again. had shop pull motor. failing leakdown test. heads sent to a new machine shop (third time heads have been machined...). pitting on exhaust valves and intake valve not seating properly in cyl 4. put everything back together and still failing leakdown in cyl 4.

    engine sent to subaru for warranty replacement. they declined and i'm still waiting to hear why. now shop is saying they'll put a new piston and rings in it and it should be fine.

    my question is this - did those 2000 miles i just drove screw up the actual cylinder wall? i'm not sure who to trust anymore. i've spent every penny i have trying to get this car driving the way it's supposed to and i'm afraid the shop is just going to throw a new piston in a bad cylinder (like subaru did before) and i'll be right back where i started...sans thousands of dollars. beyond frustrated. thanks for your time!

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    Registered User Devon4390's Avatar
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    just kinda read this twice. u mention cyl. 4 is always the culprit. may be just blowing air from my mouth but, maybe its not the block. maybe possibly a fuel issue. or maybe crank shaft or cam. whatever they didnt change when they keep repairing the engine.. whatever has been in there since day 1 is messing up thse ringlands. and could have something bent or not enough or too much fuel. or something. idk but. see if u can get a parts list of everything they changed on the car when they performed repairs.

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    the entire bottom end was swapped out. block and rotating assembly. new plugs, same coil packs and same injectors but the mechanic is assuring me that they look perfect.

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    Registered User Devon4390's Avatar
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    so everything. cams, crank, rods, bearings, pistons of course, what about top in?

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    bought brand new short block from subaru. heads/cams are re-used. they were "machined"/checked to spec when the shop installed the new block but i'm thinking they really weren't because after i started having issues with 1000 miles on the new block the motor was pulled again and an intake valve on cyl 4 wasn't seating properly. so a completely different machine shop went through the heads (3rd time) and found pitting on exhaust valves (cyl 4) and the intake valve not seating properly. they fixed the head so now the head should be completely fine but in the mean time i have ringland failure in cyl 4 and the shop is talking about just throwing a new piston and rings in it. i want to know if that's safe or not because imo the cylinder wall could be all marred up now. broken piston for 1k miles could screw up the honing...right?

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    Registered User Devon4390's Avatar
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    in most cases. the piston should be "broken" in or pretty much broken in by 1000 miles. true. now, normally on a build once you install new pistons and rings, you do rehone that cylinder and start fresh. so i would believe that yes u would have to rehone this cylinder. thing is. number 4 has issues consistantly on ur car. so, im thinking something up top is causing this. maybe cams. is it possible? im not 100% sure. but being it was a whole new block. all new lower parts. new machining and specs are met. it should have been fine. but being it has failed numerous times using the same heads, same cams. man, im starting to think something on ur cam is messed up. lobes, pitch, something. i mean. its not a good thing at all that ur engine is broken withen 1000 miles for sure, but to be the same troubesome piston after a brand new shortblock. it cant be the short block thats broken.

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    well for now, i think the plan is to get the injectors tested and valve job done on the heads then put it all back together and start datalogging to see if all is well. just not sure if i'm ok with paying for a brand new motor and not getting a brand new motor. now i'll have a motor with one cylinder ever so slightly larger than the other 3.

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    injectors came back perfect, heads are off to machine shop for a complete valve job. next, checking to see if touch honing will put the cylinder out of spec for stock pistons or not. if i can't use stock pistons i'll probably buy another stock block from subaru and sell these 2 other blocks.

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    OMG WTF MainFrame's Avatar
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    Problem with that is, those stock pistons are weak. They should be fine with a good tune, but just a small knock event, occurring regularly at a commonly used area of the powerband will cause them to crack over time.


    What have your data logs and learning view looked like on the previous engines? I know of a few cars that did not take well to the Cobb stage 1 OTS map right off the bat, and ended up cracking ringlands because the tune was bad. Blown engines which could have been prevented by simply taking a look at the logs and tweaking the map a little. Just because the tune "feels" good, and it works on other cars, doesn't mean it works on your car.

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    i have no data logs. that's something i will be doing in the immediate future. didn't know i should/needed to. i'm only ever looking to do intake, uppipe, downpipe, exhaust, injectors, fuel pump, e85. maybe 5 years from now i can retire it from dd status and have it be a project car. stock pistons should be good for this power level with a protune correct? i'm not looking to buy forged pistons if i don't have to for the power level. if the car is completely apart and it's a convenience and reliability thing then i suppose i could be swayed to do it.

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    OMG WTF MainFrame's Avatar
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    Quote Originally Posted by 07hawkeyeguy View Post
    i have no data logs. that's something i will be doing in the immediate future. didn't know i should/needed to. i'm only ever looking to do intake, uppipe, downpipe, exhaust, injectors, fuel pump, e85. maybe 5 years from now i can retire it from dd status and have it be a project car. stock pistons should be good for this power level with a protune correct? i'm not looking to buy forged pistons if i don't have to for the power level. if the car is completely apart and it's a convenience and reliability thing then i suppose i could be swayed to do it.

    Yeah, with those mods it should run good and shouldn't need forged pistons (I would add in a 3-port EBCS). At that power level, with a good tune (and good fuel(good injectors like ID1000s)) it should be more reliable on the OEM shortblock. When you tear an engine down to build it the likelihood of something going wrong increases dramatically. That said, if it were me I would probably opt to rebuild the block you have, blueprint and balance it.. with custom fit forged pistons. That would likely be cheaper than buying a whole new one. Although going that route, having a machine shop and assembler who you absolutely trust would be key.. but it would never last 200k like an OEM shortblock potentially could.

    One concern about e85 is the quality and consistency of the fuel. Not all e85 is equal.. so you might be tuned on 85% ethanol, then one day instead of 85% the gas station has e60 (60%) in the tank. If you're not testing the ethanol content and/or logging, that could be a big problem quick. I installed an ethanol content analyzer on my car for this very reason. It isn't cheap, but it gives you a real time display of the ethanol content of your fuel, so if you get some crap fuel one day you will know immediately, and can baby it, or switch to a safety map until you can fill it up with something better. You can also buy manual test kits much cheaper.. but then you have to pour some in a test tube every time you fill up.


    I don't want to see anything else go wrong with this thing. My bugeye is on engine #7 now, so I feel your pain.

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    great info mainframe, definitely have some good ideas in there to consider. i'd rather be safe than sorry cuz being sorry as much as i have been lately just plain sucks!

    let's talk about the 200k you mentioned. my only goal in the neat future is stg2 e85. assuming i drive it like a human and don't beat on it (no clutch dumping, no racing, etc) because it's my daily driver. what kind of reliability are we talking oem vs forged pistons at my planned power level? i plan on working with subaru clinic for the remainder of getting this thing up and running.

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    With a nice conservative tune, a sane driver, and good maintenance, I don't see why a stock block shouldn't last 150k+ miles. There are plenty of stage two cars with that kind of mileage and no major issues. e85 will increase the power potential beyond stage two, but the fact that it burns so much cleaner and cooler it shouldn't really put too much more stress on your engine.

    On the other hand, a built engine with forged pistons I wouldn't really expect to last much more than 60k miles.. regardless of the amount of power it's producing.

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    mainframe i really appreciate your input and will be keeping it in mind as this thing gets put together at the new shop:>

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    bought a new short block as i liked that idea better than boring the older one. sold both of my old shortblocks. new engine got installed but had misfires on cylinders 1 and 3 (never had any issue before so i'm assuming something happened during transport or install). apparently, a new coil pack fixed cylinder 1. cylinder 3 still has issues. brand new plugs, new coil pack didn't fix it, and fuel injectors all flow tested perfect. i figured something was going on with the cam or timing since both cylinders had problems and never have before but i guess we'll see what the mechanic comes up with. so weird that neither 1 or 3 ever gave me cels before and now after install they do...oem heads vacuum tested perfect.

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