P0304 shop says valve seal loose?

[whperreault]

96 impreza outback 2.2 I have been chasing a P0304 misfire code for 3 years. I have replaced the coil pack, plugs wires... the list goes on. today I took it into a highly recommended Mechanic and he said that after taking the exhaust manifold down to look inside, he saw that the valve seal had come loose, and that the engine would have to be pulled, and the manifold taken to a machine shop to have the valve reseated. has anyone ever heard of this? I have handled many jobs including rebuilding a 87 Honda Carb (I was told that this was one of the most difficult carbs to rebuild) I have never pulled a manifold. how difficult would this be, and does this sound like a reasonable explanation?

[Platinum_Racing]

The valve seal isn't in the manifold at all. It's in the cylinder head.

 

There are valve guides, which are holes bored into the cylinder head with the valve stem protruding through. One side goes to the valve's head, and the other side goes to the valve spring. To check if these are bad one would need to remove the head, pull the valve spring off, and pull the valve out. While removing the valve place one finger over the hole and completely pull the valve out of the head. If it makes a pop sound created by suction, the seal is good. Unless the car has removable oil seals pushed into the cylinder head that press into the block for the valves to slide into, you cannot see a seal through the exhaust port.

 

I'd say its time for a second opinion.

 

The PO304 code is the code for cylinder #4 misfire. Even if the engine was consuming oil it should still fire enough so that it wouldn't throw a PO304, to the best of my knowledge anyway.

[whperreault]

Sorry I was mistaken, over the phone the front desk guy said valve seal, but on the work ticket it says that the valve guide is holding the front Exhaust valve open at times. I can see how this would cause a loss of compression, but would you really have to pull the engine to get the head off, and would you need to send it to a machine shop or would a good press at a transmission shop do the trick.

 

I have very few knowledgeable options here in Eugene Oregon. I have been getting the cyl 4 misfire when I am under sustained load (accelerating onto the freeway, or accelerating up a long hill). would the high load cause a bad guide to act up, while maintained freeway speed and normal in city driving not?

[ehsnils]

"Interesting" fault, but some shops may find it easier to take out the engine to work on the cylinder heads while others may work on them in place.

 

It's mostly about how much space there is to work on it, and some people have bigger hands and arms than other people.

 

And having the engine out of the engine bay also allows the person doing the work to inspect it for other types of damage.

 

Of course - it costs more, but on the other hand it can also mean that they are probably serious about the job they do.

[whperreault]

I have decided, that due to current financial constraints, I will be doing this job myself. I have a friend with a Tranny shop that said I could use his space, and tools. I have purchased a disposable car for the interim. I am thinking of several options; the shop also reported several oil leaks, so Ideally i think pulling the engine and redoing all major seals would be best option, or pulling just the head and going to a machine shop ( I spoke to another Subie shop who recommended one ) having the Valve Guide replaced, or buying a new head and replacing it. Pulling the engine would be much more work , but I would end up with a better engine in the long run. I worry about any other warpage, and damage to the head, so I am concerned about trying to have it machined. It seems wrong to only change one head , but I dont see me having enough money to do both. what do you guys think?

[Platinum_Racing]

You bought, and registered a temporary vehicle in the hopes to keep costs down?

 

Was the quote for the repair shop really that bad?

 

I'm not judging your decision, when it comes to money you gotta do what you gotta do.

 

Replacing the heads would be a waste of money if you don't have to. If you replaced one head you would be alright, but getting one head would be expensive from a dealership. Likewise, it would be difficult to get just one online, as they are generally sold in pairs completely rebuilt with a 3 angle valve job. Here's the trick.... When you remove the engine, you have to pull the timing belt to get the head off, which means that needs to be replaced. It's a good idea to replace the water pump at the same time, as well as the tensioners and idler pulley's, which are relatively cheap. While you have the timing belt off, you might as well remove the other head anyway. If you buy just one head, clean up the combustion chamber on the opposite head. The other head will have more wear on the valve seats, guides, and other friction surfaces, but hopefully it won't die anytime soon as a result. Take the head off with the entire valvetrain intact. If you replace just one head swap the valvetrain from the old head to the new one. Check the sticking valve to see if it's bent. Extremely bent valves can be diagnosed by rolling the stem on the edge of a table. If you decide to replace both heads, some are available online online with complete valvetrains attached, which makes it easier, but more expensive.

 

You're pretty much looking at a complete top end rebuild at this point, no matter how you look at it.

 

Good luck!