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Probability of cylinder head/valve problems versus defective piston rings?

This is in regards to my 2002 Daewoo Lanos, 1.6L automatic, with approximately 91,000 miles.

This car has run poorly now for over a year, and now that I have more free time, I would like to do something about it–either fix it if it can be fixed, or else junk it and buy a different used car.

The problem is that the engine misfires a lot at idle, and the whole front end shakes violently, but once I get moving it seems to run ok. There is no visible smoke, no noticeable oil consumption, and the performance seems adequate for this type of car. It also requires several attempts to start once the engine is turned off for more than 10-15 minutes.

Thus far, I have already replaced the fuel pump (due to an inoperable fuel gauge, which the new fuel pump solved), fuel pressure regulator, and all 4 fuel injectors (due to one injector leaking a lot, and one leaking a little). None of those steps solved the engine performance issues, and of course I also replaced the spark plugs and ignition wires, etc.

Back in June, I took the car to a professional mechanic, which my employer uses, and he determined that there is an internal problem with the engine, and as a result, the spark plug for cylinder #3 gets oil on the tip, which causes a misfire. He also determined that two cylinders had approximately 130 psi of compression and two had approximately 150 psi, but the only published specification is that 100 psi is the “service limit” for this engine. He said that if I wanted this diagnosed further, I could take it to another shop, which one of his friends owns, and they could determine if the engine is repairable.

I am considering now whether it makes more sense to have this engine fully diagnosed…was quoted about $350 to do this, or if it makes more sense to assume the problem is top-end and that a DIY cylinder head replacement will make this engine run properly. I can get a remanufactured head plus the additional materials needed to do the job for about $650 including tax and shipping. I would also need to purchase a professional torque-angle tool, about $600, but once purchased, I assume this tool will last for the rest of my life since I’m just a DIYer.

Supposedly, this engine is identical to the 1.6L E-TEC used in the 2004-2008 Chevrolet Aveo, with the only difference being the porting on the head (Lanos uses an aluminum intake manifold, and Aveo uses a plastic intake manifold, and they don’t line up exactly). So I have read information online regarding engine problems with the 2004-2008 Chevrolet Aveo, and found that valve guide and valve stem seal problems are a known issue, and that a small number of people have reported problems with oil control rings.

Based upon this information, does it make sense to spend $650 on materials and $600 on a specialty tool to replace the cylinder head, without further diagnosis, to spend $350 on further diagnosis, or to just buy a different used car now? The car is in excellent condition, with no rust or body damage, and I am happy with it, except for the engine problem.

There is no evidence that this engine was ever overheated, and the valvetrain is clean, i.e. no sludge or debris under the valve cover.

Do a leak-down test on the engine.



The compression ratio on that engine is 9.6. This means that engine in good condition should have around 190 PSI. A 130 and 100 is on the way out. A 150 means it’s also headed that way; just not as bad.
In the age of unleaded gasoline and with low compression on all cylinders odds are the biggest part of the problem is in the piston rings. Oil on the plug tip generally means rings; not cylinder head. Service limits mean nothing and those published specs are incorrect. Sounds like something repeated out of Chiltons or Haynes manuals which are dead wrong and have been wrong for decades. Those publications recycle the same info no matter the car make or engine type. In a word; generic.

The professional mechanic you used should have done a wet compression test at the time he did the dry one and the answer to a ring problem would have been known then and there. If the given numbers take a 20, 30, or 40 PSI jump upwards that means rings. You should not have to spend 350 to figure this out; something that your original guy could have done in a few minutes during the original compression test. Personally, I think a reman head is a waste of money.


You also don’t need a torque angle gauge to replace a head . A torque wrench and a protractor will do unless you are going to start rebuilding engines.

Diagnose first, buy parts later. I don’t understand a mechanic doing a dry compression test and not following it with a wet one unless he discovered the engine was shot with the dry one.

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Suppose for the sake of argument that defective piston rings are the problem. How does that result in oil depositing on the spark plug electrode without any loss of oil on the dipstick, nor any visible smoke during a cold start-up? Also, is it even possible to have worn-out rings on an engine with a cast-iron block, without seeing any visible wear inside the cylinders?

I think you need to stop supposing and get that leakdown test done

It’ll answer a lot of questions, and influence your decisions going forward

And forget the idea of spending $600 for that torque wrench . . . it sounds like you’re thinking of buying a professional grade tool which might only be used once

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it doesn’t5 take much oil to foul a spark plug.

Short trip driving can mask oil loss by putting unburnt fuel in the oil. The catalytic converter burn up a fair amount of oil before it fails.

Wear doesn’t always show up as damage, sometimes it is just increased clearance.

So I bought the Maddox deluxe compression tester kit and Maddox cylinder leak-down tester kit, and my boss let me take home an old air compressor that we have at the shop which no one has used in years. The compressor unfortunately has a leak, and will not fill up past 81 psi, so I did not do the leak-down test yet, but I did do the compression test.

I removed all of the spark plugs and the fuel pump relay and disconnected the input to the ignition coil, then one at a time screwed the adapter into each cylinder and had my wife crank the ignition while I counted 6 revolutions of the engine. The results were:
Cylinder 1: 166
Cylinder 2: 171
Cylinder 3: 143
Cylinder 4: 60

Then I took a cap from a can of carburetor cleaner, filled it about 3/4 of the way with new engine oil, and poured this down each spark plug hole, and repeated the test.
Cylinder 1: 190
Cylinder 2: 192
Cylinder 3: 177
Cylinder 4: 94

Also, here are the spark plugs which I replaced on September 12 to get the car through emissions, they were NGK Laser Iridium, and had less than 4000 miles on them:

And here are the spark plugs I took out today to do the compression test, NGK V-Power copper core, and have less than 500 miles on them:

Note than cylinder 3 gets oil on the threads, even though the threads are below the sealing gasket.

Also, the engine performance became markedly worse after I had the timing belt changed, which is to say it ran like new until I had the timing belt changed for maintenance reasons. I was super-busy at that point in time, and therefore felt it more prudent to pay a shop to do the job than to risk the belt failing and ruining the engine before I would have time to do it myself (4-5 months later). The engine never really ran properly again after that, and it has gotten worse over time.

Any ideas???

Can I presume this Daewoo has hemispherical combustion chamber heads, with the spark plugs located in the middle?

If so, you could remove #4 spark plug and get a scope . . . they’re pretty cheap nowadays . . . and at least take a look at the cylinder walls

here’s a partial cut-and-paste from an alldata cylinder leak down procedure . . .

NOTE: When you adjust the regulator to “zero” the leak-down gauge, the shop air
pressure gauge will read current shop pressure. Shop pressure can be anywhere
between 60-100 psi but it needs to remain constant and steady.

That being said . . . how bad is the leak on that “old air compressor” . . . ?!

If you dial it in to build up to only 70psi, will it “remain constant and steady” . . . ?

If so, you might be able to do that leakdown test

Say . . . this engine doesn’t have adjustable valve lash, does it?


Good idea. I own an inspection camera, which I use for work. It should be small enough to fit down the spark plug hole.

The leak isn’t huge, it is at the quick-release fitting where the air hose connects. If the hose is held perfectly straight, it doesn’t leak, but if held at any angle, it does leak. The fitting is male threaded into the compressor tank, so I assume I could get a replacement, and then the compressor will work properly.

Can you please post a picture of this fitting?

Unless I’m mistaken, these fittings are easily replaced and available at any home depot, lowes or ace?

Is this a plastic quick-disconnect fitting with a red push release?

I’ve had so-so luck with them, sometimes resulting in a sizable leak unless you find that “sweet spot” . . . exactly what you described, as a matter of fact. Maybe a better quick-disconnect fitting or a regular fitting, where you have to pull the collar to release? I’ve not had leakage problems with those, as far as I can recall

according to my source, you don’t have adjustable valve lash

I ended up putting the spark plugs back in, reconnecting the fuel pump and ignition, etc. It was difficult to start the engine, and once started it smoked for several minutes, with the check engine light blinking. Now, there is something rattling inside the engine, it sounds like a rod knock, but appears to be coming from the cylinder head.

I am starting to reach the conclusion that this car will never run properly unless I replace the engine, and that is really more effort and expense than I want to deal with. The main concern is that I could shell out $800 to $1000 to replace the engine, but then never succeed in getting the car through emissions again, because it requires a CKP re-learn anytime the engine, harmonic balancer, or crankshaft position sensor is replaced or disturbed; failure to do this will result in a persistant P0300 code and flashing check engine light. The problem is that no one has the factory scan tool to do that procedure.

There are several low-cost used cars for sale here, so I will probably end up cutting my losses on this one. This car is ok, but not great, and certainly not irreplaceable. I have a truck to drive while I wait for something else to come along at a reasonable price for its mileage and condition.

When time permits, I will do the leak-down test in order to gain experience with this procedure. I will also take apart the engine to see what really happened.

There’s enough evidence to point the finger at the engine being bad even without a leak down test. Three cylinders show a ring problem and one shows a valve problem; or the mother of all cylinder/ring problems.
Generally speaking, a very low reading usually means a valve problem but that is not etched in stone. A horrible cylinder wall/ring problem can also cause very low readings.

One could bring that very low cylinder up to TDC of the compression stroke and apply some air into the spark plug hole. If there’s a valve issue you will hear it hissing out the exhaust pipe or back out of the intake manifold. Smoke can also be used to check this but I assume no access to a smoke machine.

Just an FYI, but after pricing a Snap-On smoke machine once (ouch…) I made my own on the cheap.
I bought a small stage fog machine, made an adapter for it, and after filling it with Bug Juice it works fine for things like this although the original purpose was vacuum leak checks and EVAP issues. Total cost 60 bucks…

So I am still driving this car to work every day. The engine stopped making noise after the initial run while it was burning off the oil added for the compression test. I purchased a new air compressor and air hose, and plan to do the leak-down test this weekend. I have read several websites about how to do this, but I still have some questions:

  1. How do you know if a particular cylinder is at TDC on the compression stroke, and does it really matter as long as the piston is at or near the top? I assume sticking a piece of copper pipe into the engine while I slowly turn the crankshaft should allow finding TDC or close to it.
  2. How much air pressure is it best to use? The leak-down tester tool accepts a maximum input of 100 PSI. Is it best to use something less than that?
  3. Some websites say there is a risk that the introduction of air pressure could cause the engine to turn by itself, which could be dangerous. Is removing one spark plug at a time the best way to mitigate this risk?

You can use 60 to 100 PSI. Main thing is that the pressure is steady and constant.

Yes it is possible for the engine to rotate over when compressed air is applied. Leaving the other plugs in would not make any difference as the other 3 cylinders would likely have valves open to some degree.
If you get the cylinder on exactly TDC of the compression stroke it should not rotate. A bit one way or the other and it might.

To find compression stroke I use a remote starter switch or have someone very quickly bump the key while I have a thumb on the spark plug hole; or something equivalent to a thumb. When you feel it huff that means stop and rotate by hand the rest of the way with a ratchet/socket.

A piece of copper pipe with marks will work although I tend to use a dial indicator. Using a dial indicator starts leading to the question of at what point do you quit buying tools. I have used a wooden dowel in the past. It will all work; just eyeball any marks carefully. Hope that helps.

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Get a flywheel lock. No worries of rotating crank now.

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I did the leakdown test today. All of the cylinders held pressure at 99 PSI (the most that my cheap Harbor Freight compressor could sustain) without any noticeable leakage. Any ideas now? Should I put the engine back together and disconnect the fuel injector for cylinder #4 and see if it makes any difference, especially at idle?

Also, all of the spark plugs now have oil on the threads, it appears that the valve cover O-rings are leaking.

Actually, I have to re-do the test. I used the T-handle adapter from my compression tester, I just noticed that has a Schrader in it, hence no leakage–and no air getting into the engine, either. I will remove the Schrader and try again…