Hello all,
I am looking for some advice from any of you who may have been in this situation in the past. I posted this over on clubwrx.net and 100 people looked at the post but not one had anything to offer!

I took my 2004 wrx into a shop for a tune last week and had them do a pre-dyno leakdown test. Cylinders 1,3 and 4 had numbers greater than 90% psi retained but # 2 cylinder was a 30% psi retention. Cracked/bad ring was the diagnosis. Sadly we decided to wait on the dyno tune and I picked up my car. What I do not know is what caused the dead cylinder. I am thinking a bad tune by the P/O but that is just speculation. The odo. says 170k, but car runs decent despite the issue.

Now I have about $6500 dollars into this wrx, and a dead cylinder. I am tempted to pull the short block and seat new piston rings on piston #2 and slap everything back together; this is assuming there was not much damage done to the cylinder walls or piston and it is just a ring failure... If I can get another 6 months of decent preformance out of the car that would be great.

When I have more time and more funds I will build the block with new pistons and rebuild the heads, but I want to know if any of you have gotten away with just fitting some new rings on one cylinder. I would be very tempted to get the blocked honed for slightly larger pistons, install new bearings and new gaskets but my wallet does not like that idea. Would that would be the absolute minimum for a problem like this?

That being said, If you were in my position what is the most minimal amount of heavy maintenence you would do to make yourself feel comfortable that the engine would make it another six months before a complete overhaul? Or would you say it is not worth the effort to change out one set of rings and just bite the bullet for some shiny new parts even though they are in working condition? Any input is appreciated.

 

Had a similar thing with mine last year. It was detonating under load. It ended up being the valves.

 

Interesting. I can't rule out the valves completely because I haven't taken the heads off this engine yet and checked them. What specifically failed? Were the valves bent? I am thinking the heads are okay.

 

They were burnt out and head cracked between the valve seat and the plug hole. It ran fine and it got picked up on the dyno when I was having a map. It's worth checking before you split the short block

 

Oh yeah, I have heard that can be an issue. Will definitely check the head first.
That would be small crack if it was only affecting one cylinder like in my situation, was yours split on both sides or just one? Did you have the head welded?

 

My guess would be burnt out exhaust valve/valve seat.

 

When I first got the call from the shop and they gave me the numbers that is what my first hunch was; when I stopped in to pick up the car and talked to the mechanic, he said there was some oil coming out of the exhaust at high rpms. It also will randomly emit smoke from the exhaust. I asked if he could hear air leaking into the exhaust and he said he didn't, so it probably isn't a burnt valve, but I won't really know until I dig into it.

I am going to pull the engine this week, take the head off #2 and 4 cylinders and give them a good inspection and hopefully find the cause of the leaky cylinder.

My main reason for posting was just wondering if anyone has had a broken/cracked piston ring on only one cylinder and what they did to bring the number back up. I will be working on the car this week because I have access to a shop. I want to just pop one of the pistons out, check the sleeve and piston for damage, check for clearances with the new rings and put it back together. While I could rehone the bores and install all new rings, I am just wondering if that would be necessary in this situation because the other cylinders have fairly good numbers.

 

If you're going to the effort of removing and stripping the engine I don't understand the logic in just replacing the rings on one cylinder.
Do it proberly the first time with a full rebuild and then you won't have any unwanted suprises a few miles down the road...you will only regret it in the long run buddy!

 

The logic is if it is not broken then don't fix it. If I can pop one piston out without splitting the block and leave the others alone for now that would be a better solution for the time being for me. I was just wondering if anybody has any experience with that particular issue. But maybe since one went, the others will follow closely Thanks for the input.

I guess I'll tackle the problem when I can pinpoint whether it is a head issue or shortblock issue.

 

I just got replacement heads. I didn't like the idea of having it welded. More for piece of mind really.

 

If they did a leakdown test they should able to tell you exactly if it was valves or pistons / rings, that's the idea of a leakdown test against a compression test.

 

Lol, air has to go somewhere.
My view is if the engine is coming out it will need a full set of bearings, new gaskets and all the rubbers as a minimum, especially considering the mileage and amount of work just to get 1 head off.

 

I specifically asked if he thought it was the valves or the rings and he said rings. I even asked if he heard air coming into the exhaust and the guy said no.

 

Yeah I appreciate the input. That is probably the minimum of what I would do. It just sucks cause I bought the car not expecting to have to do any work to it and then I get all stoked for my tune and find out I have a dead cylinder. I should have refused to buy the car until the guy showed me it had good numbers. You can't trust anyone these days! I might pull the engine and if it is worse than expected I will just say ^*%& it and pick up an import boxer engine off this guy in my area for $1000, and build this motor at my leisure. Then I have lots of spare parts too if need be.

 

Seeing as the car has clocked 170K, then a full rebuild would be on the cards tbh.

Mick

 

Yeah at least I have some options. Otherwise the rex is great! All the other parts work!