LNF Rebuild - Cobalt SS Network



2.0L LNF Performance Tech 260hp and 260 lb-ft of torque Turbocharged tuner version.
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Old 11-05-2017, 10:22 PM   #1
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LNF Rebuild

Welp my car is garaged for the winter. Started losing coolant so I think I'm due for a rebuild. I have done the clutch, timing chain, and other miscellaneous things on this car so I do not think a rebuild is beyond my reach. Unfortunately my garage is unheated so I will probably be doing this intermittently when the weather cooperates.

Is there a guide to rebuilding the LNF? I guess the turbo has to come off, then the timing chain removed, then the head can come off. With the oil pan dropped, I presume the cylinders can be extracted through the top? Can the rebuild happen with the motor inside the car?

Is there a how-to guide on rebuilding the motor?
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Old 11-06-2017, 09:41 AM   #2
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What year is your Cobalt? You could have the porous block problem and without a replacement block giving the engine a freshening up isn't going to stop your coolant loss. And actually the only kind of coolant leak you could potentially fix with a rebuild like you are describing is a head gasket leak. You can do a number of things including a compression test to confirm whether or not your head gasket is the problem. If you have a the right year LNF for porous block problem you may also consider trying out some block sealer additive because it may allow you to squeeze some more life out of the engine without tearing into it.

Yes you can extract pistons through the top, and yes a "rebuild" of sorts can happen with the motor inside the car. You can swap out pistons this way. However I don't really see how that is going to be of any benefit to you based on what you described. New pistons would never do anything to fix a coolant loss problem. Oil consumption is one thing but not coolant loss. Do you have other plans after this rebuild like are you going for more power? If you have good compression and no oil consumption there really is no reason to throw in new pistons. If you are honestly wanting to rebuild just to start over fresh I would strongly recommend buying a complete short block made out of a later gen better block (is it gen 3 that has the braced cylinder walls?) Swapping pistons with the engine in the car is rolling the dice and you will never get the kind of results that you would from a properly built short block. Mainly because if something is out of spec, say piston to wall clearance, there is really nothing you can do with the engine in the car or with standard garage tools. This is coming from guy who threw rods and pistons in his car which eventually led to a huge oil consumption problem. Second time around I had a shop assembly short block for me. I have an L61 but if I had an LNF/LSJ I would be all over buying a fully assembled built short block off the shelf.
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Old 11-06-2017, 09:50 AM   #3
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Second this. Figure out where the coolant is going. If it's in the oil, there is a much greater chance your block is leaking than head gasket or even oil cooler failure. A rebuild wouldn't help in that case.
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Old 11-06-2017, 03:17 PM   #4
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The block sealer mentioned really clogs up everything in the cooling system, to include interior heater core, reduces radiator performance, may partially clog the coolant-to-oil heat exchanger and will also permanently reduce the cooling efficiency of the head as it tends to coat the coolant passages with the copper material and is extremely difficult if not impossible to remove. On a car destined for the junkyard that you need to get another thousand or two miles it might be worth it but not in something nice or high performance.

If it's a gradual coolant loss you definitely want to determine where it's going like suggested in the last couple posts. Lets assume it was a cracked or porous block leaking internally. If it was slowly getting into the oil and burning off the oil would still show signs even if it isn't the regular milky consistency. And easy way to tell would be to send an oil sample in to a testing lab like Blackstone for a used oil analysis. They'll be able to tell right aware if there's trace signs of coolant in the oil.

If there is coolant in the oil there's a chance it could be a head gasket but it's not as likely as it once was decades ago on cars that used composite/organic type head gaskets. The newer multi-layer steel based gaskets generally don't tend to leak or weep coolant and oil between passages and have a more common failure mode of catastrophic failure.

If the OEM Dex-Cool coolant was never changed and became acidic (or was changed and topped off with a different, non-organic acid technology (OAT) coolant) there is a slight chance the heat exchanger (i.e. oil cooler) may have corroded. I'm trying to go off memory but I think you could temporarily connect the two hoses and bypass the exchanger to rule it out. Since it's getting to be winter if you're driving it just make sure to give the engine more time than usual to warm up.

The turbocharger's center section could also theoretically crack and allow coolant to leak into the oil but I'd also say that almost a zero chance. To rule out you could pull the drain tube and visually inspect for milky mixture of oil and water.

Also be sure to rule out any other source of external leaks before writing off the engine block. Make sure the coolant system is working correctly and possibly use some tracer dye and a blacklight to inspect for hidden leaks. If it leans towards being the block or you want to build an engine for performance it might be wise to start with a newer GM crate engine and possibly do some upgrades from there, as needed, to support your power levels. That also reduces the potential problems and hassles with finding a good machine shop and you get everything new that would start adding up if you had to buy to put in your block (assuming it is usable).
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Old 11-06-2017, 03:35 PM   #5
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If his block is leaking I think it would be worth gumming up the radiator and heater cores very slightly to get a lot more life out of an otherwise trash block. I have used K-seal before and during tear down I did notice a slight coating in certain locations but it did not noticeably reduce the cooling system/heater core performance nor did it plug/block anything off. I'm the same way about additive stuff like this but in the case of having to get a new block vs. getting thousands more miles out of this one the risk/reward is worth it IMO.
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Old 11-06-2017, 11:10 PM   #6
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I apologize in advance for this long wall of text, but it provides important background information. My car is a 2010 LNF with full bolt ons, and tuned by a SSKEV.

Back in July, my old turbo puked a lot of oil when I was at the track and there was some shaft play. Based on this, I replaced the turbo with a new one. About four weeks later, the engine started consuming oil, about 1 quart every 1000 kms. More so if I really pushed the car. I had suspected at the time that my PCV valve was bad so I replaced both it, and the fresh air inlet check valve. The PCV valve was indeed bad, but replacing it did not cure the oil consumption. The new turbo is still good in terms of shaft play, and the drain line is still good. Chances are that the new turbo is still good.

I ran a compression test tonight and got some really wonky numbers. This is at 660ft above sea level. Two full cranks on each cylinder, cold motor, outside about 3 deg. C.

Cyl 1 145#
Cyl 2 150#
Cyl 3 138#
Cyl 4 172#

Not sure what is up with Cylinder 4, unless it is normal and the first three are low.

I pressurized the cooling system with a tester to 15 psi but could not find any leaks. The floor was dry. Oddly enough the coolant level did not go down either. Seems to only lose coolant with the engine running.

I had let the car sit overnight before draining the oil today hoping that any water would separate from the oil. However, the oil that came out was black and consistent with what I have been seeing during past oil changes. That being said, I do think that there is coolant in my oil. Rubbing the oil between my fingers feels different compared to used oil from a good engine. I also did a quick "blotter" test using a drop of oil on newspaper and can see differences in dispersion. I just expected more obvious changes given the amount of coolant I lost.

The car is now sitting in my garage, and I do not have the luxury of driving it because I switched my registration to another car. Any further tests will have to be done in-situ.

The LDK long block from ZZP is very attractive, but shipping to Canada is insane.
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Old 11-07-2017, 09:01 AM   #7
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I was going to recommend a LDK. It might be worth the drive down to ZZP to pick one up
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Old 11-07-2017, 10:25 AM   #8
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Quote:
Originally Posted by LTBALTBMX View Post
Two full cranks on each cylinder, cold motor, outside about 3 deg. C.
According to everything I have seen this is not enough cycles to get a proper reading. This article recommends 6 to 8 compression strokes.
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Old 11-07-2017, 12:13 PM   #9
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The throttle blades need to be fully open for an accurate reading, and off memory I'm not sure if cranking at wide-open throttle will cause the electronic throttle to fully open. You also generally want to keep cranking until the gauge stabilizes, say about five seconds or so. I'd repeat the test with the cold engine, then let it slightly warm up and repeat. The warm test is a better indicator of piston ring sealing after they expand closer to normal operating temps. Because of the variable cam timing you also want to start off running the engine for about 30 seconds or so before all testing to make sure the system is pressurized along with the hydraulic timing chain tensioner so cam timing is accurate.

I've personally had very poor results over the years spotting a minor head gasket leak with a compression test on multi-layer steel (MLS) and MLS coated gaskets. Beyond the compression test, you can also do a leak-down test which pressurizes a cylinder and checks how well it holds pressure before normal leaking down. Compression is a good indicator of engine health, while leak-down testing can help spot leaks and verify poor compression.

If you do have poor compression it's likely rings, damaged bore (which I'd assume would damage the rings), crack in the piston ring lands, leaking direct injector seal, or the intake and exhaust valves not sealing. With the direct injection carbon build-up problems it might be wise to pull the intake manifold and see how the intake ports looks. There are also inexpensive bore cameras that can be used to visually look inside the combustion chamber.

As for the oil, it's extremely difficult to tell from smell or touch the condition. If you didn't drain all of it or saved a clean sample it might be wise to send it to a testing lab for analysis. You'll get a lot of good information on overall health of the engine internals and will be able to pinpoint if there's even trace amounts of coolant getting into the oil.
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Old 11-07-2017, 08:56 PM   #10
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According to everything I have seen this is not enough cycles to get a proper reading. This article recommends 6 to 8 compression strokes.
When I say two cranks I mean I held the key until the cutout kicked in (approximately 15 seconds each). This is adequate.

I have done this previously with a warm motor and got similar results. Still don't know what is up with cyl 4. Why is it so high?! My compression results from two years ago were not this high.
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Old 11-07-2017, 09:06 PM   #11
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Quote:
Originally Posted by LTBALTBMX View Post
When I say two cranks I mean I held the key until the cutout kicked in (approximately 15 seconds each). This is adequate.

I have done this previously with a warm motor and got similar results. Still don't know what is up with cyl 4. Why is it so high?! My compression results from two years ago were not this high.

did you use the same compression tester?
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Old 11-07-2017, 10:07 PM   #12
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did you use the same compression tester?
I didn't but I had consistent numbers on cyls 1 to 3.

With my shitty smart phone borescope I looked inside. Cyls 1 - 3 were very dark, couldn't see much. Cyl 4 looked relatively clean but again couldn't see much.
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Old 11-07-2017, 10:53 PM   #13
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Could be carbon excessive carbon buildup. Try a leakdown test
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Old 11-07-2017, 11:52 PM   #14
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I would never rebuild an lnf unless u swap in a gen3 block. don't spend money on rebuilding an lnf block that is known for porus block
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Old 11-08-2017, 08:06 AM   #15
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I thought the 2010s were safe from the porous block issue?
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Old 11-08-2017, 08:08 AM   #16
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Could be carbon excessive carbon buildup. Try a leakdown test
This is probably it. My turbo was puking oil for the last two months. However cyl 4 looks relatively clean. I wonder if coolant leaked into it which cleaned out the carbon?

Im going to pull the head pretty soon. Before I do, are there any other tests I should do?
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Old 11-08-2017, 09:21 AM   #17
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Before I do, are there any other tests I should do?
Leak-down test like everyone keeps suggesting.
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Old 11-08-2017, 01:12 PM   #18
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Will do but none of the local stores carry them. Gotta keep looking
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Old 11-08-2017, 01:43 PM   #19
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Old 11-08-2017, 11:16 PM   #20
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Just ordered a leak dpwn tester from Amazon. Odd that Canadian Tire nor Princess Auto sells them anymore.

Im not sure what the leakdown test is supposed to acocmplish. It wont telll me whether my coolant leak is due to a porous block or blown head gasket. I thought the 2010s didnt suffer from porous blocks? Im at 180k km by the way.
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Old 11-09-2017, 08:03 AM   #21
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Old 11-09-2017, 03:04 PM   #22
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Both the compression test and also the leak-down test aren't guaranteed to show if your head gasket is leaking, but of the two the leak-down test is much more likely to show a small or slower leak. It can also help pinpoint if you have carbon buildup or leaking rings causing the disparity in the compression test.de

Also as mentioned earlier, unless the engine oil is milky it can be tough to go off appearances and feel. I'd still recommend a used oil analysis to tell for sure if and how much coolant is getting into the crankcase. It will also give a good general idea of engine health and if there's any other internal wear issues. The price has gone up a touch over the years but it's still pretty reasonable for just under $30 at Blackstone for example.
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Old 11-12-2017, 05:32 PM   #23
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Did a leakdown test today. Registered 37.5%, 33%, 34%, and 34% on cylinders 1 through 4 respectively. While doing the test, there was air flow coming from my dipstick tube. I'm not sure whether piston rings are supposed to be air tight so I can't tell whether this is normal or not.

I would take the numbers with a grain of salt as I have noticed that this Amazon tester is not very repeatable.

No bubbles from the coolant tank while I tested each cylinder.

I drained my oil on Wednesday and re-fitted the drain plug. Today I re-opened the drain plug and more oil came out. It was the consistency of used oil, with no evidence of coolant. However, my coolant levels did fall since Wednesday because I had pressurized the system with the tester. Where the hell is all the coolant going?!

Will send my oil off for analysis hopefully this week.
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Old 11-13-2017, 09:24 AM   #24
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So you drop pressure and lose coolant when you pressurize the coolant system? If you lose a significant amount of coolant you should be able to find out where it is going. You could level off your oil on the dipstick, make sure it has time to completely settle so you make sure to get an accurate reading. Then hook up your coolant system to pressure and let it sit like that until you lose a significant amount of coolant. Once you notice it is down enough check your oil again and see if it is reading higher. If it's not in the oil and sounds like it can't be in the combustion chamber, then it would have to be leaking on the exterior somewhere.

I think normal results for a leak down test is to have air slip past the piston rings as long as it isn't too much.
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Old 11-13-2017, 12:35 PM   #25
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20% or above and your rings are junk
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