Replace The Valve Stem Seals on a 91-93 GMC Syclone Typhoon

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The valves in your cylinder head are there to regulate the amount of fuel and air mixture into your engine. Each of these valves have rubber sleeves (or guides) to ensure that gases from combustion dont leak past them as well as keeping oil in the valve cover from being sucked down into the engine.

Over time, these seals become worn. If you notice a puff of white smoke on a cold startup, you most likely have bad seals. This is caused by residual oil that has leaked by the worn seal and into the combustion chamber. The white smoke is the oil being burned off. This will also happen during extended periods of idle and stop/go traffic when the oil under vacuum accumulates and gets pushed past the seals and then burned off during initial acceleration.

This article explains how to replace your valve steam seals in a Chevrolet 4.3 V6 engine.

  • Magnetic Pick Up Tool
  • Air Hold Tool
  • Valve Stem Seal Pliers (GM 4.3 Specific) Kent-Moore EN-46116 shown
  • Valve Stem Seal Installer (GM 4.3 specific) Kent-Moore J-42073 shown
  • Valve spring compressors - I used 2 of them. The first one is the standard Craftsman one. It has the handle. It was decent to use at best, however DOES have the staggered arms at the bottom making it easier to use. The 2nd was the generic Autozone one. That was needed to do the cylinder closest to the brake booster. There is no way you can get the 1st on in there. This one I cut the handle off of and just used the 3/8 ratchet attachment. This one DOES NOT have the staggered arms at the bottom and was a challenge to get to grab the springs just right.
  • Viton Fel-Pro Valve Seal Set - SS72876
  • The intake ones are labeled intake/exhaust, but should only be used on the intake. They resemble the stock ones you are removing. The Exhaust ones are labeled only exhaust on the box. They are a hard plastic with rubber inside.
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Remove valve covers. Move as MUCH around them as possible. This makes things alot easier.


Remove the upper fan shroud and fan to get to the crank pulley.


Remove spark plug at the cylinder you will be working on. You will need to hand turn the motor over each time you change cylinders. You need to try and get the piston to the top before filling with air. This will keep your valve from falling all the way in if you loose shop air. I have heard of using rope shoved into the spark plug hole, but this way worked well for me. Make sure that both valves are closed or you will not be able to hold air pressure to work. I also used a flashlight to see the piston at the top of its stroke looking through the spark plug hole.


Remove rocker arms and set aside. Make sure you put each piece back EXACTLY where it came from (including the pushrods), when you reassemble.


Install air hold tool and pressurize to around 80psi. I had originally used 90lbs, but I could hear the motor turn a little due to the high pressure.


Install valve spring compressor to expose the valve keepers. They may be stuck. I used a brass bar and a hammer to lightly tap on them to break them loose.

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Remove the keepers using a magnet. BE CAREFUL not to drop them!

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Remove the valve spring. Some of mine got stuck and I would have to take the compressor off to remove the spring. This will expose your valve seal. All valves have a very small O-ring on them. Remove them with a small screwdriver--they are brittle and will probably break as you tap them.

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Use pliers to remove old seal.

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This pic shows the need for 2 different valve spring compressor tools. Notice how the brake booster limits room to use the compressor with handle. This is #5 cylinder.

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Installing New Seals


Install new seal. Use the special tool to lightly tap on INTAKE seals so they seat right. DO NOT use them on the new exhaust seals. I got my first one stuck in the tool until I realized they only fit the intake ones. For the exhaust seals, just press them on very tightly by hand. You might be able to do the same with the intake ones, but if you have the tool, use it!

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Install the small supplied O-ring on the bottom groove of the valve stem.


Reinstall the spring and keepers. The keepers have to fit and click in just right, so take your time if they dont go in right away. Have patience on this step.


Release tension of the compressor SLOWLY and make sure that the keepers sit correctly. Give them a slight tap to make sure.


Reinstall rocker arms and pushrods. Make sure to use a magnet when installing the pushrods. I have actually lost one into the lower intake years ago and now I am paranoid. I also used a flashlight to visually assure that they were sitting properly in the lifter.


Adjust the valve lash. Tighten nut until you are no longer able to move the push rod up and down. Then give it about a 1/8th turn after that. You should still be able to rotate and spin the push rod slightly. If not, back it off slightly. Thanks to Dave Perry for that tip.

Replacing valve seals is not a job to undertake if you are unfamiliar with basic engine mechanics or DO NOT have the correct tools for the job. If done incorrectly, engine damage may occur. This video can be used for reference. The seals are different, but the process is similar.

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For adjusting valve lash:

"Get the little plastic clip on plugs for keep oil from shooting everywhere. With the valve cover off, rockers tightened a half turn past finger tight, start the engine (it will sound like absolute shit but that's OK), one by one tighten the rocket nut down until the noise stops and then go 3/4 turn past to secure it.

Congrats, you've hot lashed it and now go drink beer." - Stanford Logan

"The best way to get the most accurate lash on our trucks is by hot lashing them. Stanford Logan is correct. Just a couple small details I will add that have come from time and experience. Put the rocker nut on, with approximately 2 threads showing at the top, this will be loose, but not too far off or risking nut backing off. Go on by one, until the noise stops, wait 15-20 sec for the lifter to pump up, then go 1/2 turn more. The book say 1 full turn, we have found that to be a bit too tight in these set ups. With bigger cams 1/4 turn is enough, but on stock heads, stock cam, stock rockers, I have found 1/2 turn past works great. HTH" - Thomas Mandrov

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