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-   -   Bad Exhaust valves on the LGT? (http://legacygt.com/forums/showthread.php?t=126764)

sleepermaxima 12-10-2009 01:45 AM

Bad Exhaust valves on the LGT?
 
Immediately after purchasing an 05 LGT with 84K on the clock it turns out that the #2 Exhaust valves were pulverized and no longer making a decent seal against the seats. Once the tech tore the heads off he found that #4 wasn't much better and the #1 and #3 cylinders were starting to show the same signs of deformation.

I have been told by the dealership that this issue is rare on these cars but just this last week another LGT was brought in with that same issue to that dealership. And I was told by the tech that my new valves will more than likely suffer the same fate as the originals due to the hardness of the valvesprings on those motors.

So this is making me wonder if this is an issue that anyone else has been running into yet?

I'm wondering if this issue is only rare because it's more rare to have an 05+ LGT with that many miles

GTTuner 12-10-2009 10:28 AM

Stock tune? What octane fuel do you use?

sleepermaxima 12-10-2009 11:31 AM

Yup, everything is bone stock. 91 octane... 92 isn't really available up here anymore.

Deaks2 12-10-2009 12:45 PM

The car may have been over-rev'ed.

GTTuner 12-10-2009 01:19 PM

My thoughts exactly, although my engine saw 8000rpm once (missed a shift) and didn't bend any valves.

sleepermaxima 12-10-2009 02:53 PM

I don't think that is the issue. Sure, over-revving causes valves to float and hit the pistons... that is not the same as valves rolling. I was told the the exhaust valves show the slow progression of the deformation when they are all out and you can compare to the valves from other cylinders. Over-revving causes an immediate valve failure that bends the valve or the edge of the valve towards the valve seat. These valves are failing by bending the opposite way - away from the seat. This means the valves are failing by hitting the valve seat, not the piston.

I haven't seen the valves in person yet so I am going off what the tech said. They are saving the valves and have taken pics of the cylinder walls, pistons and other items of interest since i cant be there to see it myself. Once I see the valves and pics for myself I will let you know if the damage is consistent with floated valves.

GTTuner 12-10-2009 03:14 PM

Lets see what causes a valve to burn:

1. Valve clearance too tight.
2. Detonation
3. Possible cam timing off and the exhaust valve opening before the combustion event has completed
4. Shitty initial valve sealing when the engine was new.
5. Carbon deposits on the stems not letting the valve fully close.

I'm sure I'm missing a few possible causes but pictures are worth a thousand words.

Some of the above would have other symptoms before damage was done.

Ridgeracer 12-10-2009 05:41 PM

First I have heard of this. In for pics.

j255c 12-10-2009 07:12 PM

On my original engine i had a few non sealing valves.

I believe what caused this-

A huge lean condition when my fuel pump failed out at 24psi w/ meth 15:1 a/f
Lots of power
Detonation
Subaru engine gremlins

GL OP.

sleepermaxima 12-19-2009 01:08 AM

3 Attachment(s)
K, got the valves back. The stems are totally straight from what I can tell. The burned valve is a tad deformed; albeit, uniformly deformed... not bent or lopsided. It appears that it has been essentially been getting pulled through the head to the point where the diameter is smaller than original as it has sort of mushroomed up. 7 of the 8 valves measured are 32.02mm to 32.09mm in diameter. The burned valve is 31.71mm. Maybe this is attributed to blow-by erosion on the valve too.

I would like to think this was due to abuse or something environmental as I don't want to have to deal with this issue again if I should keep the car for a long time. But wishful thinking hasn't served me too well so far.

The thought at the dealership is that either the valve was too soft or there was some sustained high rpm driving by the previous owner... or something else like an out of spec spring, anyway, here are the pics.

The first one is one of the OK valves. The black one is the burned valve. (duh)

NSFW 12-19-2009 01:15 AM

First I heard of this kind of thing. :confused:

ehsnils 12-19-2009 02:17 PM

If you have a faulty injector that gives less fuel than the others you may get burnt valves.

But it may also be that the valve in question did fail some stage in production and wasn't caught in quality control.

sleepermaxima 12-19-2009 08:46 PM

Yeah, that cylinder could have gotten pretty hot at one point.

I swiped the service history on this car so I know the #2 injector was replaced because of the P0302 code. It may have been replaced based on "let's try it and see if that helps" or it may have actually be tested and found NG.

Its pretty much impossible to know for sure what caused it with the resources that I have. But the injector idea makes the most sense.

If it was a clogged injector I imagine this issue could be more and more common as the LGTs get up there in mileage. The owner of whichhunter said he has never once come across a bad yellow-top bowl-fed injector from a subaru but they can get clogged just like any other injector.

Hotchico 12-20-2009 03:33 PM

I had my first injector issue at about 35K, starting to get a rough idle again now at 66K, but also need to get the 60K service so the plugs could be causing the idling issue

chuckzul 12-26-2009 06:30 PM

Quote:

Originally Posted by ehsnils (Post 2752455)
If you have a faulty injector that gives less fuel than the others you may get burnt valves.

But it may also be that the valve in question did fail some stage in production and wasn't caught in quality control.

This is exactly what I think happend to my Legacy. The #4 injector slowly failed over a period of time until it failed completely causing the car to throw a P0304. By then, it was too late. The #4 cylinder had only 45# of compression. I suspect the other exhaust valves are probably not much better. I think this is a serious engineering flaw on Subaru's part as I've had no problem with my WRX wagon. Rather then spend the $1400-2000 to fix this one issue, I decided to trade in the car for a Dodge Ram. Not as much fun, but easier to fix and probably more reliable in the long run.


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