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Old September 9th, 2007, 14:08   #1
NYTDIBoy
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Default What's involved in changing out the Valve stem seals?

Hi,

Been battling a soot issue with my car since I owned it and I think I am down to only 1 or 2 major culprits. The major one is the valve stem seals. I think they are bad because I have observed an awfully high pressure (and volume) of air comming out of the CCV.

So has anyone done this job? If so, how bad is it? I assume it involved everything in a TB job, plus removing the cam?
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Old September 9th, 2007, 14:48   #2
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When valve stems seals go bad the usual problem is excessive oil consumption. But on a diesel engine with a turbo there is a positive pressure in the intake manifold instead of the vacuum that exists in a gas engine. Thus a diesel engine does not develop the vacuum to suck oil down the valve stem into the intake manifold. Nobody replaces valve stem seals in a diesel - even diesels without a turbo.

How many miles are on your jetta? How much oil are you consuming?
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Old September 9th, 2007, 14:55   #3
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Quote:
Originally Posted by Mad_Dasher
Nobody replaces valve stem seals in a diesel - even diesels without a turbo.
Please be more accurate. The guy that rebuilds our heads at work always replaces the stem seals.

That's just one guy, but I bet if you asked frank06, he will tell you that he always replaces stem seals.

That's two guys, but if you ask anyone that has replaced valve guides in an ALH head, you will find that they too replace the stem seals.

To say "Nobody replaces valve stem seals in a diesel" is just plain wrong.
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Old September 9th, 2007, 15:06   #4
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I have the same question, as I am using about 1 quart every 2000-3000 miles. Compression is 490/490/490/490. ('03 Jetta). Haven't done a leak-down. What else should I be checking if it is not the valve seals? Not seeing much smoke outside of normal puff when I step on it. Car seems loud to me (sounds like a diesel), especially at start up. Acceleration is OK, (auto).

I was reading about this in my Bentley's manual this morning. It indicated that leaking valve stem seals is a major source of excessive oil consumption in the TDI. It indicated it occurs during decelleration with smoke evident when you let up on the go-pedal

Last edited by sdeck; September 9th, 2007 at 15:12.
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Old September 9th, 2007, 16:32   #5
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If you are suffering leaky valve seals it is probably time to check the rest of the cylinder head components.

I replace valves ( or at least re-face), valve guides and valve seals when head is removed.
The time and money is but a pittance _now_ compared to doing it a year or two later and having to do the timing belt job and replacing the head gasket as well a second time.
And while you are at it have a multi angle valve job done ( 3-way)

Here is a "dummies guide to valve work" -
http://home.hiwaay.net/~langford/corvair/valvejob.html

A similar analogy would be changing oil but not replacing oil filter.

Robert

Quote:
Originally Posted by whitedog
Please be more accurate. The guy that rebuilds our heads at work always replaces the stem seals.

That's just one guy, but I bet if you asked frank06, he will tell you that he always replaces stem seals.

That's two guys, but if you ask anyone that has replaced valve guides in an ALH head, you will find that they too replace the stem seals.

To say "Nobody replaces valve stem seals in a diesel" is just plain wrong.

Last edited by rjr311; September 9th, 2007 at 16:35.
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Old September 9th, 2007, 16:34   #6
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The "High" blow by (crank case pressure) is not related to bad valve stem seals. "High" is subjective. It may be normal. Diesels, due to high combustion pressures, have more blowby and may seem high to most people.

The only reason to consider replacing valve guide seals is because of high oil use, and in a diesel, valve guide seals do not control oil as much as in a gas engine, since there is no intake manifold vacuum to suck more oil past the seals than would flow from gravity (like in a gas engine).

If your engine does suffer from excess blowby, it is probally from worn piston rings/cylinder bores. Oil consumption should be high as well.

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Old September 9th, 2007, 16:38   #7
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Quote:
Originally Posted by sdeck
I have the same question, as I am using about 1 quart every 2000-3000 miles. Compression is 490/490/490/490. ('03 Jetta). Haven't done a leak-down. What else should I be checking if it is not the valve seals? Not seeing much smoke outside of normal puff when I step on it. Car seems loud to me (sounds like a diesel), especially at start up. Acceleration is OK, (auto).

I was reading about this in my Bentley's manual this morning. It indicated that leaking valve stem seals is a major source of excessive oil consumption in the TDI. It indicated it occurs during decelleration with smoke evident when you let up on the go-pedal
"It indicated it occurs during decelleration with smoke evident when you let up on the go-pedal"

That applies to gasoline engines. When the throttle closes in a gas engine (when you take your foot off of the gas) on engine over run, a large manifold vacuum develops and this sucks oil past worn valve guides and bad VG seals.

Also, I would imagine a pluged/kinked turbo oil return line or worn turbo bearings/seals could increase consumption, as well as oil leaks.

You can replace the valve guide seals with the head on the car. Cam comes off and lifters come out. Each cylinder is done at TDC and the valve keepers released, springs are removed and the seals replaced. On the diesel, the valve will rest right on the piston top. On a gas car, compressed air (or a nylon rope inserted into the cylinder thru the spark plug hole) keeps the valve from falling into the cylinder. You do need several special tools to do this, though.

--Nate
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Last edited by PDJetta; September 9th, 2007 at 16:43.
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Old September 9th, 2007, 16:58   #8
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Whitedog,

I agree if your rebuilding the head, of course you would replace the seals. I was answering in the context of the question posed in the post. I wasted time one afternoon replacing the valve stem seals on my dasher. It was of no help in slowing oil consumption. No throttle plate means little of no intake vacuum. Thus the seals are rarely a problem on a diesel. But I would, however, insist they be replaced on a rebuilt head.
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Old September 9th, 2007, 17:01   #9
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Thanks. That's why I think that clarity is important; it makes for less confusion.
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Old September 9th, 2007, 17:25   #10
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I appreciate it when I am mentioned by name as someone who 'knows'... thanks, whitedog...

Here is the thing that most people seem to misunderstand about a turbo'd engine. There is no oil sucked into the engine from valves. There is constant pressure that goes through the intake and exhaust valves into the crankcase. That means BLOW-BY. That can cause a lot of oil consupmtion by pushing oil into the intake manifold by way of the crankcase vent (CCV).

I just took apart a head that I know must have been having a lot of oil consumption simply because the CCV would not be able to handle all the crankcase pressure pushing oil into the intake manifold and therefore, causing excessive oil usage by burning the crankcase oil. It was simply the excessive clearance between the valve stem and the valve guide that caused this issue.

If you have valve guides that are so worn that there is a substantial amount of blow-by, I am not so certain that valve guide seals are going to cure your problem. I think that the pressure from the crankcae venting is going to overcome the springs holding the valve seals in place.

Although I do always replace the valve guide seals when rebuilding a cylinder head, I think to do seals without considering the valve guide is to do things in half-steps. The valve guide has more to do with blow-by than does the valve seal. As a matter of fact, I think that the valve seal is superfulous. Even though I always install them, I think they are of little consequence.

I think that a close tolerance between valve stem and valve guide and a very accurate and concentric cutting of valve sealing surfaces would drastically reduce oil consumption and leads to long valve and valve guide life.

I am also a very strong believer in the aftermarket Crank Case Vents that are available. The small CCV atop the valve cover is simply not large enough to handle the demands of the engine, especially an engine that has been modified for additional horsepower.

A agree that valve stem seals can be replaced without removing the head, but doing seals without taking care of the underlying cause is futile.
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Old September 9th, 2007, 17:36   #11
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I agree. Putting new valve stem seals on worn out valves mounted in worn out guides won't do a thing.

It is possible there is some oil ring soot built up, and there is only one method I know of short of an overhaul that can help with that.

BG makes a "compression restorer" that introduces and EXTREMELY powerful substance into the engine oil, and if used properly can loosen and remove the crap built up in the rings. I am not a big advocate of additives, but the BG stuff actually does work.

Also, there may be some oil blowing past the turbo seals, although usually that goes pretty quick when it happens.
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Old September 9th, 2007, 17:37   #12
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Quote:
Originally Posted by NYTDIBoy
Hi,

Been battling a soot issue with my car since I owned it and I think I am down to only 1 or 2 major culprits. The major one is the valve stem seals. I think they are bad because I have observed an awfully high pressure (and volume) of air comming out of the CCV.

So has anyone done this job? If so, how bad is it? I assume it involved everything in a TB job, plus removing the cam?
"Soot" is an indication of overfueling or not enough air, or retarded timing. Turbo problems, mis adjusted injection timing, and worn injectors can cause black smoke. Oh, plugged air filters (or snow screen) can cause it too.

--Nate
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Old September 9th, 2007, 18:38   #13
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If blue smoke on startup is the case and you go ahead and replace only the stem seals, are you going to have to redo the job later because the worn guides weren't replaced? To rephrase, can your seals go bad and still have good valve guides?
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Old September 9th, 2007, 19:21   #14
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Frank, I was thinking the same thing on valve guides. Saw a Cat 3304 that had two guides so worn, the end of the valve had probably 3/32 inch play. Exhaust soot was in big gobs around the valves.

Of course the block with holes on each side was what finally made them shut it down.
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Old September 11th, 2007, 18:01   #15
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Quote:
Originally Posted by PDJetta
"Soot" is an indication of overfueling or not enough air, or retarded timing. Turbo problems, mis adjusted injection timing, and worn injectors can cause black smoke. Oh, plugged air filters (or snow screen) can cause it too.

--Nate
I figured Overfueling or not enough air. The car has been chipped, but even before it sooted pretty bad. I do the timing belts myself, have all the correct tools and check the timing advance with my VAGCOM, everything appears to be fine. The car get's 47-49 mpg consistantly in mixed highway/city driving. Oil consumption is minimal (about 1 quart every 10,000 miles), and I don't seem to have any power problems. The car now has 170k on the clock. I know nothing about the first owner or how it was maintained. Got it with a bit less than 60k on the clock and when I did the first TB I pulled and cleaned the intake because it was pretty clogged and had the MAF changed under warranty. I also pulled the snowscreen out soon after getting the car so it's not clogged. I keep a good eye on the filters and change the air filter every oil change (sometimes every other if it looks clean enough).

The only time the car soots real bad is under moderate to high acceleration. It is not nearly as noticable in the higher gears as it is in the lower gears. The reason I ruled out overfueling is the cars consistant and high mileage. When I saw what seemed to me to be real high CCV pressure I thought it might be pressure from the intake leaking out past the valve stem seals. That's what led me down the not enough air path. other items on the not enough air path would be sticky VNT vanes ("actual" boost levels vs "requested" boost in VAG-COM seems to track nice in the high gears) or maybe a badly clogged intake again. I'm hoping neither of those is the case though as the power doesn't seem to be lacking and VAG-COM readings all appear normal.

How about an exhaust problem? The car has the original full exhaust on it. What would a clogged or failing cat do?

The other choice is the worn injectors. I seriously thought about ordering a set of injector tips from TDiParts with my order the other day, but didn't. My reasoning against the injectors was the high mileage. I thought if the injectors were dirty that the mileage would be poor, but I have been known to be wrong before!

Thanks for all your help with this problem that has been bugging me since I bought the car!
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