Valve stem seals removal with head still on block

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Old 07-21-08, 12:37 AM
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Valve stem seals removal with head still on block

Any tips or tricks on removing the valve stem seals with the head still on the block? I've done several head gasket jobs in the past, but I've never attempted to replace the seals with the head still on.

I know I can use compress air to keep the valve from dropping. I've also heard of feeding a nylon rope into the cylinder and bring the piston to TDC on compression stroke. Even with the heads off, it can be a challenge seperating the retainer and keepers and that's my fear, trying to seperate the retainer and keepers.

If it matters, I have a 91 S10/Sonoma with a 4.3. For the past several months I have been getting a puff of blue smoke during cold start. By the time I put the truck in gear and drive out the driveway the blue smoke will disappear. As the months go by, the puff of blue smoke is getting bigger. But it still disappear by the time I drive down the block.
 
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Old 07-21-08, 03:44 AM
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there are compressors (really an improper name. it is more like a bar with holes in the right places) that can be used as a lever to compress the spring and retainer. While compressed, the keepers are removed and the spring released.

you have the right idea with the air or rope. If using air, have the piston at TDC as well because if you remove the retainer and lose air pressure, the valve will fall and depending on how long he valve stem and how long the stroke, you may lose it in the cylinder. Most likely not since most valves have enough build-up on the stems to prevent it from falling through but why chance it.

I prefer the rope because if using air, if the retainer is stuck tight, you can still push the valve down sometimes as the air prssure does not provide enough resistance to break the retainer free.
 
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Old 07-21-08, 04:03 AM
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If the valve retainers are stuck you can tap on the top of the spring with a hard rubber hammer, this will loosten them. Be sure and have the air/ rope already in the cylinder because sometimes the locks will fall out when you tap the keeper down.
 
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Old 07-21-08, 03:06 PM
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Usually a Valve spring compressor available at any parts store for under 20 bucks will suffice. Its looks alot like a battery terminal puller, but a bit heftier.

Compress the spring , tap the top of the compressor with a Hammer, and a "Pocket Magnet" will do the rest.

In 25 years. I have never had a problem with using air to hold the valves up....Although it is possible.

If the piston youre working with is up at TDC during the whole procedure, a "Dropped "valve will only fall as far as the piston will allow...Which leaves the stem accessible with a Magnetic tool and some Patience.
 
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Old 07-21-08, 05:28 PM
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Same as "Unclediezel ", but have a couple of questions before you put yourself through all that work. Is it only on cold start-up that you get the blue smoke? If you idle for a period of time, does it also do it? Does it do it at stop signs, then take off? Does it do it when engine is warmed up?
 
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Old 07-21-08, 05:55 PM
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Thanks for the reply. I have all the tools (spring compressor, hammer, pocket magnet, pick tool, etc) patience and confidence to do the job. I just wanted to hear from those who have actually done the job to see if there are tricks of the trade in accomplishing the task.

Unclediezel, that's a good point with the piston beng at TDC.

Mike B,
-yes it's only during cold start up
-it does not smoke during idle
-it does not smoke while pulling away from a stop light/sign
-it doesn not smoke when the engine is at operating temp.

Some other basic info. The compression and vacuun is good. It deosn't smoke when going WOT. It does not smoke at high engine vacuum (high road speed and closed throttle)
 
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Old 07-22-08, 05:23 AM
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=Unclediezel;1400840]Usually a Valve spring compressor available at any parts store for under 20 bucks will suffice. Its looks alot like a battery terminal puller, but a bit heftier.
use caution if you release the spring though. It may be taller than your compressor once freed and it may also fly.



In 25 years. I have never had a problem with using air to hold the valves up....Although it is possible.
Neither have but I can see a retainer being stuck well that requires a really good tap and somebody "tapping" the valve stem hard enough to break the air seal.

If the piston youre working with is up at TDC during the whole procedure,
Oh, I see. UncD gets a pat on the back for saying the same thing I did earlier. Where's my kudos?



If using air, have the piston at TDC as well because if you remove the retainer and lose air pressure, the valve will fall
Just kidding. I get paid the same either way.
 
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Old 07-22-08, 04:38 PM
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Candiman ! Having read your answers to all my previous questions, I have to admit, if it were me, I'd be hesitant about changing those valve seals. Instinct & past experience tells me it's something else causing that puff of smoke on cold start-up only. I know the old 350 chevy engines were pretty well known for valve seals, and from what I'm told, the 4.3 is basically same engine minus 2 cylinders, but a puff of smoke on cold start-up only, tells me to look for something else. Perhaps there is some more 4.3 owners out there who have experienced same symptoms who can confirm your suspicions, and perhaps if you do it anyway, you'll prove me wrong. You don't have any injectors leaking down at night by chance do you? Remember too, oil gets thinner when warmed up to operating temperature. Thinner oil, warm engine, high vacuum, no smoke, when you would think those are all the conditions when oil should have a better chance of getting by the seals?
Hate to make you second guess it, but food for thought. Maybe some of the others in this post can add or dispute my thoughts to this. I remember a vehicle I owned (not a 4.3 ) did basically same thing, and it turned out that fuel was dripping from a couple of injectors in the night, or after sitting for a few hours & cooling off, washing down oil in cylinder, causing it to stumble a bit & smoke on cold start-up, but then all was well after a few seconds of running, and oil got circulating again, and unburned fuel burned off. Good luck ?
 
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Old 07-22-08, 06:22 PM
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You said it, 350 are known for bad seals and yes, the 4.3 is a 350 minus two cylinders. I am a member of a Chevy/Blazer S10 forum, and it never dawn on me to ask the same question in that forum. I will do that a post the replies here. Your injector leaking down at night is a viable posibility, but when I cold start the engine it does not stumble, hesitate or stalls. My engine is a TB fuel injection unit.

"Thinner oil, warm engine, high vacuum, no smoke, when you would think those are all the conditions when oil should have a better chance of getting by the seals?"

I couldn't agree with you more on this statement. My only explanation is that as the engine cools down and the valve seals shrinks, any residual oil on top of the valve spring and seal area will slowly drip pass the seal and into the cylinder.

Once the engine starts, the heat will expand the seal to where it will not smoke durng a high vacuum situation.

Unfortunately I'm not planning on doing this repair anytime soon. Just trying to get some insight and opinions.

Thanks.
 
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Old 07-22-08, 07:29 PM
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I have to agree that it is most likely the valve seals causing this condition. Simply stated while everything is sitting still and relaxed is when the oil slips by the seals.
I have done valvetrain service MANY times with the heads still installed. Not on a 4.3, but they are all basically the same. I have a leakdown tester that I use to hold the cylinder. I put the cylinder at TDC and hook up the tester. Turn the regulator to hold 100psi. I have never had to use anything to release a sticky retainer other than the valve compressor I am using. I have had the valve come off of the seat, but the air pressure has always been enough to reseat the valve as soon as I release the compressor.
Hope this helps ya,
Billy
 
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Old 07-23-08, 06:17 PM
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I did a search on the S10/Blazer forum. The general census does point to the valve seals. I reas one post that said if it smoke at start up, it's the seals. If it smokes at idle, it's the valve guides. If it smoke while driving, it's the rings.
 
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