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Transportation

Lesson Plan Originally Created By: steve nagle

**Remove and Replace a Valve (updated) by Steve Nagle

Part of Unit: Engine Systems

Lesson Plan Overview / Details

This lesson will explain the steps to remove and replace an engine valve from an overhead valve engine.

Instructional Time

Classroom/Lab
2 Days

Objectives/Goals

Students will be able to remove and replace valves in an overhead engine

Instructor's notes

Selecting the proper tools and working safely

Always wear eye protection while performing this job. Safety glasses are required as there is a good chance the valve spring compressor may slip. If the valve spring compressor slips while depressing the valve spring the spring, keepers, or retainer may be projected at high speed. Always make sure the spring compressor fingers are pointed away from yourself or anyone nearby.

Locate the spring compressor. There are two styles: Mechanical and Pneumatic.

Activities in this Lesson

  • _iceUrlFlag=1.jpg   After locating the spring compressor, take it to your work area.  The cylinder head should be removed and placed on the workbench.

    Adjust the fingers on the spring compressor so they fit snugly around the valve spring.  Most valve spring compressors have a thumb screw that will widen or narrow the fingers. 

     

    Resources and Materials

  • Locate a soft faced hammer.  Strike the valve tip to loosen the valve keepers/locks.

    CAUTION: Do not strike the valve at an angle, as you may bend the valve stem!

  • The valve spring compressor has an adjustable foot located opposite the fingers.  Place the fingers of the valve spring compressor on the valve retainer.  Adjust the foot so it lightly touches the valve head.

  • In order to remove the two tapered valve locks the spring must be compressed.  On the manual valve spring compressors move the handle upwards (towards the fingers).  On pneumatic valve spring compressors locate the depress and release buttons.  Activate the buttons before trying to remove the valve spring to see how far the piston extends.

    Resources and Materials

  • Depress the valve spring compressor.  If the valve compresses, locate the two tapered valve keepers/locks and remove.  If the spring does not depress, it may be hanging up on the old valve oil control seal.  While compressing the valve spring, tap lightly on the valve compressor fingers with a soft faced hammer.  This will break loose a stuck valve retainer.

  • Releasing the valve spring compressor jaw tension with the keepers/lock removed should allow the spring to relax.  If the valve spring compressor tension is released and the valve spring does not release its tension, the retainer is hanging up on the old valve oil control seal.  

    DANGER: If the valve spring does not relax when the valve spring compressor is removed, there is a potential of the retainer and valve spring to be projected at a high rate of speed.  

    If you should encounter a hanging valve spring, cover the spring with a shop rag.  Carefully tap in the tip of the valve stem with the rag over the tip.  When the tension is released the spring will be caught safely in the rag.

    I have had valve springs fly off across the shop and break a window across the room!

  • Removing the valve Demo / Modeling

    _iceUrlFlag=1.jpg   After removing the valve spring, keepers/ locks and retainer, remove the valve oil control seal.  On GM products this seal consists of a small rubber "O" ring located just under the groove where the valve locks rest.  With other applications, there is a rubber umbrella seal on the stem resting near the cylinder head.

    Before attempting to remove the valve, inspect the valve tip.  If there is a mushroomed area on the tip, remove it with a fine file.  Inspect the keeper/lock grooves as well.  Burrs in this area can damage the valve guide if not smoothed before removing the valve.  If any roughness is present, smooth with emery cloth.

    When any burrs or roughness is removed the valve should slide easily down and out of the cylinder head. 

     

  • Inspecting the valve Demo / Modeling

    After removing the engine valve inspect it.

    Look for obvious damage from burning.

    Look for evidence of valve guide wear.

          - Buildup of carbon on intake valves indicates oil getting past the guide and seal.

          - Grooves at the top of the valve stem indicate a loose valve guide.  Dragging your thumb nail across the valve surface helps to find wear that cannot be readily seen.

          - Spin the valve in an electric drill.  If the valve wobbles it is bent.

          

  • cleaning the valve Demo / Modeling

    After concluding that the valve is serviceable, remove any carbon deposits with a wire brush. A pedestal  grinder with a wire brush works great.   If the deposits are hard to remove with a wire brush, I have used an old valve as a chipper to knock off the hardened deposits.

    Wire brush the face area.  If using a power brush, use caution and brush on the downward side, tilting the valve head a bit so the brush doesn't grab the valve out of your hand.

    Do not attempt to glass bead a valve unless you protect the stem with a tight fitting piece of rubber hose. Removing the polished finish will shorten valve life.

  • Engine Valve reassemble Demo / Modeling

    _iceUrlFlag=1.jpg   After the valve guide is inspected, cleaned, and serviced the valve seat can be ground to the manufacture's recommendation.  After the valve has been inspected, cleaned and the face and tip machined, verify there is enough margin. Test valve spring tension and free length. Verify seat and face contact to be correct. It is now time to reinstall the engine valve.

    Completely clean all parts.  Lubricate the valve stem will light oil or a thin coat of assembly lubricant.

    Slide the valve into the head.  Install a new oil seal. Install any valve spring shims if necessary.  Install the valve spring. NOTE: Some valve springs must be installed a specific direction.  Verify valve spring installation with manufacture's specifications.

    After the valve seal and spring are properly installed, place the retainer in top of the valve spring.

    Place the valve spring compressor foot on the valve head and the fingers on the valve retainer.

    Carefully compress the valve spring.  Make sure if it slips off it will not injure yourself or those working around you.

    If you are using the valve seal "O" rings, install them in the lower groove at this time.

    Place the valve keeper/locks tapered side up (thin part down).  Hold both keepers/locks with your finger and thumb.  As you slowly release the compressor, the locks will seat themselves. 

     

    Don't be afraid of getting pinched.  The released compressor will push your finger and thumb as it is released.

    Gently tap the valve stem with a soft faced hammer to seat the keepers/lock.  Failure to do so may result in the valve locks coming off.  If this happens when the engine is running, the valve will drop into the engine cylinder with catastrophic results .

Testing Valve job

Assessment Types:
Demonstrations,

After all valves have been installed successfully in the cylinder head all valves keepers/locks seated with a soft faced hammer, it is time to test the valve/ face seal.

Install a spark plug in the cylinder head.  Block any exhaust cross over passages.  Fill the intake runners from the intake manifold side with solvent.  Inspect to see if the liquid level stays at the full level.  Inspect the valve head area.  Is there any wetness? If there is evidence of valve to face leakage remove the valve and determine the cause of the leak.  When filling the exhaust runners the center runners have a cross over passage that must be blocked.  If flooding the intake and exhaust runners is not practical flood the combustion chamber with the head level.  Verify leaks by wetness in the intake or exhaust runners.

Final inspection and job completion

Assessment Types:
Observations,

After the cylinder head has been tested using the wet method, it is important to clean off all solvent and place the head in a plastic bag to prevent corrosion build up.  When you are ready for the head installation they will be free from dust/dirt.

Return all tools to their proper location wiping off any oil or dirt.

Make sure the work area is cleaned off wiping down the work benches with degreaser.