N12 Nightmare cylinders 1&4 misfire after head gasket replacement
 

Hi. This is my first post here, looking for help with a never ending problem.

Warning: Long winded and frustrating

I own a 2007 hatchback with an N12 in it. The head gasket went out last year and caused misfires and rough idle to the point it was undrivable. so after a long and difficult teardown the gasket was replaced and the engine reassembled. the car refused to start. Ive triwd simple things like replacing the gas as it sat for quite a long time. Nothing.

The engine was reopened and all sensors and wires inspected. The timing was recheckedand verified and during the inspection a small fuel pressure was found. all injectors seals were replaced along with clips. the engine still had a misfire in cylinders 1&4. At this point I brought in a mechanic to look at the car and it was found that 3 of the hydraulic lifters were bad, and were replaced. after the cams and variable intake side was reinstalled, the misfires still persist.

After vigorous cussing, I purchased a leak down tester and went to work on testing all cylinders. The results are:

Cyl 1: 65percent leak with a small amount of air making its way into the intake manifold and also leaking through the oil drain holes below the cam

cyl 2: 22 percent leak couldnt pinpoint a source and cyl still generatss combustion

cyl 3: 30 percent leak same as cyl 2

cyl 4: 58 percent leak from the oil drain holes under intake cam

The injectors are delivering fuel and all the coilpacks and sparkplugs are still firing. I am at the point where I do not know how to procede with the project. I really want to get this car working for my woman, she loves the car and is the only reason I havent dumped the car yet.

Any ideas or assistance would be immensely appreciated, thanks.

Take a deep breath brother...We'll figure something out, eventually.
Could you describe how the timing was checked?
when you open the doors, do you hear it priming like a quick pump spin?
Have done a compression test?

I built a crank locking pin and cam locks to put the car back together, trying to save money incase I have to replace more expensive parts. So far I have not done a compression test, it was apparent the cylinders had low compression just by covering the spark plug holes of cylinders 1 and 2 at the same time and feeling the difference when cranking the starter.

when the doors are opened there is a brief humming which I am assuming is the fuel pump. The gasket on one of my injectors was bad and sprayed fuel everywhere so i know fuel is moving to the injectors. when attempting to start, the plugs for 1&4 will be wet with fuel , it just isnt getting combustion. 1&4 on the exhaust manifold are cold to the touch while 2&3 will be warm.

On timing job, when you turn your crank to align flywheel into locking position for the insert key, did you also open up all spark plug holes and place equal height long sticks like zip-ties or kabob sticks? you need to check piston height as you turn the crank. The key can be inserted into lock position at 0 and 180 degrees of crank position. And depending on which one you're in, you could have completely missed the timing with the cams. I can be wrong as this is what I've been doing with the N14 engine, not sure if N12 would be same but it's good to think about that and check it. I did see others perform their timing job and missed it this way.

I did use wires to measure the piston height. and it does make 2 circuts before coming back into allignment. How would I confirm that i have it on the right way vs having it 180 out?

Look, I rebuilt a dozen of these engines and not a single one had "two locking holes"!!! UNLESS you have an after market flywheel. So, to test the locking holes, count how many times it locks the flywheel and at what piston level.

once you lock the crank shaft, then you need to make sure the cams are facing up where the locking tool would sit snug.

try to do it the way you did it before and post pictures :)

If you have it 180 out, piston 1&4 will be a certain height and 2&3 will be opposite height. I don't remember which one is high or lower position, though. But if you have it at 0, then they will all be in same height.

the timing for the n12 is set at middle of cylinder and im only getting a misfire from 1 and 4 so I done think its timing related the leakdown test showed a slight leak from intake valvss kn 1 and 4 though. would timing off affect just those 2 or would it leak from all 4 cylinders?

if timing is off, all cyls would be effected. At this point I'm leaning towards bent valves. I think your initial issue was not a head gasket, but rather something else, the timing chain.

Im starting to think the same thing. the head gasket may not have been the primary issue and only caused another failure. I am planning to remove the head to swap out my valves and valve components on 1 and 4 on the intake side.

while you have it off, it is worth checking the exhaust side as well. better same than sorry :)

I have the head completely off at the moment and am waiting for my valve compressor tool to come in. Do yall think it would be a good idea to swap my cylinder rings out and refresh the pistons and walls while its all taken apart?

Do a leak down test on the cylinders, if there aren't any leaks, don't go tinkering what ain't broken.

when performing the leak down tests, most of the leaking was happening through the intake side. After inspecting I found there is one bad valve in each of the misfiring cylinders. There was a small air leak coming from the oil drain holes under the valve cover leading me to believe the rings are worn out. The motor has 220K on it. Im just trying to avoid opening up the nightmare machine again in the near future.

I think it's best to do it since you're already there.

Leak down tests you performed are on the head with respect to the valves. Your previous question asks if while you took the head out should you replace the piston rings. In my reply, the leak down test I'm referring to is with respect to the piston chambers themselves. You can poor carb cleaner in each chamber, and see if there are any leaks over time. If that performance is good, it means you don't need to replace the rings, just focus on the head valves. That would be my choice of strategy.

After searching for ever. I finally found the source of all of my woes. The valve seat in my number 4 cylinder dropped out and was crushed into little pieces and spread throught my cylinders. It no longer sealed on the number 4 and a large piece traveled through into the number one and was crushed into tiny pieces which got stuck in the piston rings and into the valve seals. Amazingly the cylinder walls are still intact and have no scratching. my piston rings and pistons werent so lucky, the pistons have marring on the top surface from the metal pieces and my piston rings came out in pieces while cleaning out the cylinder bores.I have a machine shop set to do the new seat next week. all the exhaust valves and the intakes in 2 and 3 are still sealing perfectly. I may reseal them when putting the head back together. Hopefully this is it.

That cylinder wall may still need to be looked at, possibly honed before you press the new piston and the rings in. With the valves, make sure you lap them, too. Little extra precarious step here and there will get you a long way down the road.

Ive got new valves coming with a tool and im planning to lap them all in after the seat gets replaced. Ive pulled all the ring sets and am planing to rehone the inside to get the cross hatch back. Theres no vertical marks so I shouldnt have to get too agressive with it. just wanna make sure that when i get all the parts back together I dont have to reopen the nightmare machine again for a good while.

I have a similar issue, but we cannot find a source for the valve seats; where were you able to locate them?
?

When the seat dropped it destroyed the inside of the head in all of the cylinders on mine, as well as the piston heads and rings. I decided against repair at that point as a motor from a dismantler was 1k cheaper than parts to fix the motor. If you decide to go with repair. I recommend finding a engine or metal shop to do it for you. They will remill the head and custom make a hardened steel valve seat and ensure they’re properly fitted and done. At that point though all of the seats should be redone to prevent another one from dropping out in the future. The shop quoted me $400 to do the valve seats. That price doesn’t include filling in and remilling the indentations in the head caused by the old valve seat being crushed into little shards.

Do you have the name of the shop that gave you that quote- I could call them to see if they have a source for the valve seats?

The shop custom makes them to ensure they’re a perfect fit. Most engine and metal shops can make them for you. Then the head is milled so they fit together perfectly. A stock valve seat can’t go into the space where the old one dropped out as it wouldn’t fit right enough in the old slot. The shop I contacted makes the valve seats a few microns larger then presses them in so they’re mated almost permanently.