Cylinder Head Disassembly; Inspection of the Valve Train

CYLINDER HEAD DISASSEMBLY

On some OHC engines, the rocker arms must be removed before the head is disassembled. If the cam shaft rides directly above the rocker arms, use the appropriate spring compressor and depress the valve enough to pull the rocker arm out (33). Some have the rocker arms mounted on a separate shaft. The ends of the rocker arms don’t directly con tact the valves; rather a bridge rocker arm is used. The bridge rocker arm assembly is also mounted on a shaft. To remove these rocker arms, both shafts are unbolted (34).

On all OHC engines, the camshaft must be removed before the cylinder head can be disassembled. Follow the specified order for loosening the camshaft bearing caps. Keep the caps in the order they were on the head. Also, draw a diagram of the arrangement of the cam follower assemblies and mark each part. This will ensure that each part is returned to the same position.

Measure the installed spring height for each valve and record it (35). This measurement will be needed during reassembly. To remove the valves from the cylinder head, use a valve spring compressor. First, select a socket that fits over the valve tip and onto the retainer. Tap the socket with a plastic mallet to loosen the valve keepers. Adjust the jaws of the compressor so they fit securely over the spring retainers. Compress the valve springs just enough to remove the keepers.

Next, remove the valve oil seals and the valves.

Keep all assemblies together according to the cylinder they were in. If a valve does not pass through its guide, the tip might be mushroomed or peened over and have a ridge around it. Don’t drive the valve through the guide. It could score or crack the valve guide or head. Raise the stem and file off the ridge until the stem slides through the guide easily (37).

Aluminum Cylinder Heads

!WARNING! Aluminum cylinder head bolts should never be loosened or tightened when the metal is hot.

Doing so may cause the cylinder head to warp due to torque changes.

Fgr__36 With a spring compressor, compress the springs just enough to remove the keepers.

Mushroomed tip

Fgr__37 A mushroomed valve tip should be (A) filed before removing the valve from (B) its guide.

Fgr__38 Checking a cylinder head for warpage.

Inspection of Head:

Cylinder heads should be carefully inspected after they are cleaned. Any severe damage to the sealing and valve areas indicates that the head should be repaired or replaced. Also use the appropriate method for detecting any and all cracks. Check the heads for dents, scratches, and corrosion around water passages.

As engines undergo heating and cooling cycles over their life span, certain parts tend to warp. This is especially true of cylinder heads. By using a precision straightedge and feeler gauge, the amount of warpage can be measured. The surface should be checked both across the head as well as lengthwise (38). In general, maximum allowable deformation is 0.004 inch (0.1016 mm). Check the manufacturer's recommendations for the maximum allowable warpage for the engine you are working on. Many manufacturers recommend head replacement if it’s warped beyond allowable limits. Also check the flatness of the intake and exhaust manifold mounting surfaces.

Aluminum heads experience fair amounts of thermal expansion, which can lead to cracking. The most crack-prone areas are usually the areas around the valve seats (39). High-combustion temperatures and the constant pounding of the valve against its seat often cause cracking between the intake and exhaust seats or just under the exhaust seat.

Aluminum has another drawback-porosity. The casting process sometimes leaves microscopic pores in the metal, which can weep oil or coolant. In most instances, the problem is only cosmetic and does no real harm. But the customer may not agree. To the customer, a wet spot on the outside of a cylinder head looks like a leak.

Aluminum heads should be carefully checked for dents, scratches, and corrosion around water passages.

Also, they should be checked for warpage. Warpage in an aluminum cylinder head is usually the result of over heating (low coolant, uneven coolant circulation within the head, a too lean fuel mixture, and incorrect ignition timing). For aluminum heads, the maximum allowable warpage is less than it’s for cast-iron heads.

Always check the cylinder head thickness and specifications to be sure that material can be safely removed from the surface. Some manufacturers don’t recommend any machining; rather they require head replacement if cylinder head flatness is not within specifications.

Aluminum heads can be straightened through the use of heat and special clamping fixtures. However, some manufacturers don’t recommend this.

Alignment of the cam bores in an OHC head should be checked with a straightedge and feeler gauge. If the bores are more than 0.002 to 0.003 inch (0.0508 to 0.0762 mm) out of alignment, corrective action is required.

Fgr__39 Lightweight aluminum heads are prone to cracking. This can lead to a recessed exhaust valve seat.

Fgr__40 Severely burnt valves. Valve face angle; Head diameter. This line is parallel with the valve face; Check stem tip for spread; Check for thin (worn) lands between the keeper grooves; Check for bent stem; Check stem diameter at three locations on the stem

Fgr__41 Parts of a valve that should be checked during your inspection.

Valves:

Each valve face should be carefully checked for evidence of burning (40). Also check the entire valve for signs of wear or distortion (41). Replace any valves that are badly burned, worn, or bent. Also discard any valve that is badly burned, cracked, pitted, or shows signs of excessive wear. Carefully examine the facings on the stem. If the plating is flaking or chipped, the valve should be replaced.

Examine the backside of the intake valves. A black oily buildup in the neck and stem area indicates that oil is entering the cylinder through the intake valve (42) or valve guide seats. Measure the mar gin left on the valve. Valves that cannot be refaced without leaving at least a 1/32-inch (0.79 mm) valve margin should not be reused. Reusable valves are cleaned by soaking them in solvent, which will soften the carbon deposits. The deposits are then removed with a wire buffing wheel. Once the deposits are removed, the valve can be resurfaced.

When replacing a valve, make sure the new one is an exact replacement for the original. This includes the stem diameter, stem height, head diameter, and the material used to make the valve. The first three items can be measured and compared. However, it’s not easy to identify the metals used for the valve.

Replacement valves should be made from the same or a better alloy than the original valve. A good starting point to identifying the metal is to see if it’s magnetic or not. Stainless steel is nonmagnetic, while carbon steel is magnetic.

Valve Seats:

Valve seats should be checked for damage, cracks, burning, and deterioration. Also, check insert seats for looseness in their bores. This is done by prying on the inside of the seat. With moderate pressure there should be no movement. If any damage is found on the seat, a new insert seat can be installed. If an integral seat is damaged, the area around it will need to be cut out and an insert seat installed. If the seat appears to have sunk too deeply in its bore, it needs to be replaced.

A seat should also be replaced if its valve was bro ken or bent. This may have been caused by the seat not being concentric with the guide. This causes the valve stem to flex every time the valve closes.

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Fgr__42 An oily soot or heavy carbon buildup on the back of the valves indicates bad valve seals. Carbon buildup

Fgr__43 Common valve spring designs.

Deviation

Fgr__44 Spring squareness test.

Fgr__45 Valve spring height terminology: (A) free height, (B) valve closed spring height, and (C) valve open spring height.

Fgr__46 Various forms of timing belt wear.

TIP: When making any change in hopes of increasing horse power, especially a cam change, don’t forget to install stiffer valve springs. Higher-tension springs will help keep the lifters in contact with the cam lobes and over come the increased momentum of the valves and the valve train during high engine speeds. Match the springs' tension with the engine. Excessive spring tension is not good. It can put too much stress on the cam lobes, lifters, rocker arms, and so on, and cause them to wear prematurely.

Always follow the recommendations of the cam shaft manufacturer when replacing valve springs.

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Retainers and Keepers:

Valve spring retainers and valve keepers hold the valve spring and valve in place. The retainer holds the spring in line with the valve stem. A worn retainer will allow the spring to move away from the centerline of the valve. This will affect valve operation because spring tension on the valve won’t be evenly distributed.

Each retainer should be carefully inspected for cracks, since a cracked retainer may result in serious damage to the engine. The inside shape of most retainers is a cone that matches the outside shape of the keepers. This must be a good fit in order to secure the keepers in their grooves on the valve stem. Both the retainers and keepers should be inspected for wear and dam age. They should be replaced if a defect is found.

The valve stem grooves should match the inside shape of the keepers. Some valves have multiple keeper grooves. Others have only one. All of the valve stem grooves should be inspected for damage and fit by inserting a keeper in them.

Valve Rotators:

When valves are refaced or replaced, the rotators should be replaced because they cannot be accurately inspected. Whether or not they rotate by hand is no indication of how they actually function. Uneven wear patterns on the valve stem tip are an indication that the rotators are not working properly.

Valve Springs:

The valve spring assemblies (43), including the damper springs, should be checked for signs of cracks, breaks, and damage. The high stresses and temperatures imposed on valve springs during operation cause them to weaken and sometimes break.

Rust pits will also cause valve spring breakage. To determine if the spring can be reused, the following tests should be performed.

Freestanding Height Test--Line up all the springs on a flat surface and place a straightedge across the tops.

Measure from the table top to the straightedge. Throw away any spring that is not within specifications.

Spring Squareness Test: A spring that is not square will cause side pressure on the valve stem and abnormal wear. To check squareness, set a spring upright against a square (44). Turn the spring until a gap appears between the spring and the square.

Measure the gap with a feeler gauge. If the gap is more than 0.060 inch (1.524 mm), the spring should be replaced.

Open/Close Spring Pressure Test: The procedure for checking valve spring open and close spring pressure is given below. Close pressure guarantees a tight seal. The open pressure overcomes valve train inertia and closes the valve when it should close.

Spring pressure specifications are listed according to spring height (45). Any spring that does not meet specifications should be replaced.

INSPECTION OF THE VALVE TRAIN

When inspecting the valve train, each part should be carefully checked. Use the following guidelines when inspecting the components.

Timing Belts:

Most often, the belt is replaced when the engine or head is rebuilt. Stripped/broken belt failure is commonly due to insufficient tensioning, extended ser vice life, abusive operation, or worn tensioners. Most manufacturers recommend timing belt replacement every 60,000 miles. Loose timing belts will jump across the teeth of the timing sprockets, causing shearing of the belt teeth. Check for cord separation and cracks on all surfaces (46) of the belt. Also check for evidence of exposure to oil or water. Both can cause deterioration of the belt. If the belts are contaminated or damaged, they should be replaced.

On many engines, severe engine damage will result from a broken timing belt. When a timing belt breaks, the camshaft no longer turns, but the crank shaft continues to rotate through inertia. When the camshaft stops, the valves stay where they were when the belt broke. This means some of the valves are open. As the pistons continue to move, they can strike the open valves. This results in bent or broken valves and/or damaged piston domes.

SHOP TALK -- The condition of a rubber timing belt can frequently be checked by the fingernail test. Press your fingernail into the hardened backside of the belt. If no impression is left, the belt is too hard; this is caused by overheating and aging.

HOW-TO:

Measuring and Fitting Valve Springs (continued)

-7 If measured installed height is greater than the specifications, a valve shim must be placed under the spring to correct the difference.

-8 Spring tension must be checked at the installed spring height; therefore, if a shim is to be used, insert it under the spring on the valve spring tension gauge.

-9 Compress the spring into the installed height by pressing down on the tester's lever.

-10 The tension gauge will reflect the pressure of the spring when compressed to the installed or valve closed height. Compare this reading to the specifications.

-11 Now compress the spring to the open height specification. Use the rule on the gauge or a scale to measure the compressed height.

-12 Compare this reading to specifications. Any pressure outside the pressure range given in the specifications indicates that the spring should be replaced. After the tension and height have been checked, the spring can be installed on the valve stem.

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Fgr__47 The timing chain on some engines should be measured in sections while it’s being stretched. 15 links 4.54 in (115.4 mm)

Fgr__48 A timing belt tensioner assembly.

Mounting collar Belt tensioner; Attaching bolt

Fgr__49 Timing chain components. No. 1 chain sub-assembly

No.1 chain vibration damper

Chain tension slipper

Crankshaft timing sprocket No. 1 crankshaft position sensor plate

Chain tensioner and torsion spring No. 1 chain tensioner assembly

No. 2 chain sub-assembly

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Timing Chains:

Each drive chain should be inspected and replaced if it’s damaged. The length of the chain should also be checked. Some manufacturers recommend measuring the entire length of the chain and comparing that to specifications. The chains on other engines should be measured in sections while they are being stretched.

To do this, pull the chain with the specified tension.

Then measure the length of the specified number of chain links (47). This measurement is taken at three random sections of the chain. The average length is then compared to specifications. The chain should be replaced if it’s not within specifications.

Belt Idler Pulley:

All idler pulleys should be rotated by hand. They are okay if they move smoothly. The pulley should also be checked for signs of lubricant leakage. Check around the seal. If leakage is evident, the idler should be replaced.

Tensioners:

The tensioners of belt and chain drive systems should be checked. There are many types of tensioners used in today's engines; refer to the service information for the correct inspection procedure. Check the surface of the tensioner's pulley. It should be smooth and have no buildup of grease or oil (48). Most belt tensioners should also be checked for signs of lubricant leakage. Check around the seal. If any damage or leakage is evident, the tensioner should be replaced.

The action of a belt tensioner should be checked.

Make sure the spring is free to move the tensioner pulley. If the tensioner spring is defective, replace the tensioner. On plunger-type tensioners, hold the tensioner with both hands and push the pushrod strongly against a flat surface. The pushrod should not move.

If it does, replace the tensioner. Measure the distance the pushrod extends from the housing. Compare that distance to specifications. If this measurement is not within specifications, replace the tensioner.

Chain drive systems have a variety of dampers and guides in addition to a tensioner (49). The dampers and guides should be checked for wear. In most cases, their width is measured and compared to specifications. If they are worn, they should be replaced. Again, there are different types of chain tensioners, each with a unique inspection procedure.

The plunger in ratchet-type tensioners should be able to be smoothly moved out by hand but should not be able to be pushed in by hand.

Gears and Sprockets:

All timing gears and sprockets should be carefully inspected. A gear with cracks, spalling, or excessive wear on the tooth surface is an indication of improper back lash. All damaged or worn gears should be replaced.

The oil pump, camshaft timing, crankshaft timing, and balance shaft gears and sprockets on some engines are measured with the drive chain wrapped around the individual gears. The diameter of the gear with the chain around it’s measured with a vernier caliper. The caliper's jaws must connect the chain's rollers while doing this. If the diameter is less than specifications, the chain and gear or sprocket should be replaced.

Cam Phasers: Camshaft phasers are used in most VVT systems. The action of a hydraulic phaser can be checked while it’s attached to the camshaft. Clamp the camshaft in a soft-jawed vise. Attempt to rotate the timing gear on the phaser. If it moves, the phaser must be replaced.

Next, cover all of the oil ports on the phaser with electrical tape except the advance port (50). Using an air nozzle with a rubber tip, apply the specified air pressure to the exposed port (51). The timing gear should move counterclockwise.

When the air is released, the timing gear should move clockwise. This check should be conducted several times and the timing gear should move smoothly.

This process is then repeated at the retard port. In this case all ports, except the retard port, are sealed.

Cam Followers and Lash Adjusters: Overhead cam follower arm and lash adjuster assemblies should be carefully checked for broken or severely damaged parts. If pads are used to adjust the valve lash, the cups and the shim pads should also be carefully checked. A soft shim won’t hold the valve at its correct lash; therefore, the hardness of each shim should be checked. You can do this by placing a shim on the base circle of the camshaft and, with your hand, press down on the shim. You should feel no give.

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Fgr__50 Location of the advance port on a camshaft phaser. Advance side port; Timing gear; Air gun Fgr__51 The action of the phaser is checked by applying air to the port and observing the timing gear.

Inspect rocker arm roller for wear; Measure rocker arm bore Fgr__52 Measure the inside diameter of the rocker arm and check for an out-of-round condition.

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Rocker Arms:

Inspect the rocker arms for wear, especially at points that contact the valve stem and pushrod. Make sure the oil feed bore in each rocker arm is clear and not plugged with dirt. The fit between a rocker arm and its shaft is checked by measuring the outside diameter of the shaft and comparing it to the inside diameter of the rocker arm (52). Excessive clearance requires replacement of the rocker arm or the rocker shaft, or both. Another wear point that should be checked is the pivot area of the rocker arm. Also check for loose mounting studs and nuts or bolts. Replacement press-in studs are available in standard sizes and oversizes. The standard size is used to replace damaged or worn studs and the oversizes are used for loose studs.

Excessive wear on the valve pad occurs when the rocker arm repeatedly strikes the valve tip in a hammer-like fashion. This is caused by excessive valve lash due to improperly adjusted valves or bad hydraulic lifters. Worn rocker arm valve pads can also be caused by poor lubrication. Although a cast rocker arm can be resurfaced, a stamped nonadjustable rocker arm that is worn must be replaced.

Honda's Variable Cylinder Management Rocker Arms: Honda uses oil pressure and two sets of rocker arms to alter cam timing and to deactivate cylinders.

This system has unique inspection and service procedures. When inspecting them, keep all parts in order so they can be installed in their original location.

Measure the outside diameter of each rocker shaft at the location of the first rocker arm. Then measure the inside diameter of the rocker arm. The difference between the two is the clearance. This clearance should be compared to specifications. Repeat this procedure for each rocker arm and shaft. If the clearance is beyond specifications, replace the shaft and all over-tolerance rocker arms. If one rocker arm needs replacement, all of the rocker arms on that shaft should be replaced.

Next, inspect the synchronizing pistons in the rocker arms. Slide them into the rocker arms; they should move smoothly. If they don’t or are damaged, the rocker arm assembly should be replaced. The rocker arm oil control solenoid has a filter. This should be checked and replaced if it’s clogged.

Pushrods:

During inspection, some pushrods may be found to have a groove worn in the area in which they pass through the cylinder head, and some may have tip wear. Also, the ends of the pushrods should be checked for nicks, grooves, roughness, or signs of excessive wear. All damaged pushrods should be replaced. Hollow pushrods should be thoroughly cleaned so there are no blockages in the bore.

Check the straightness of each of the pushrods.

Bent pushrods can be caused by incorrect valve timing, valve sticking, or improper valve adjustment.

Bent or broken pushrods can also be caused by the use of incorrect valve springs or if the valve's installed height is less than specified. Also, insufficient valve to-piston clearance can cause a collision between the valve and piston at high engine speeds.

Pushrods can be visually checked for straightness while they are installed in the engine by rotating them with the valve closed. With the pushrods out of the engine, they can be checked for straightness by rolling them over a flat surface such as a surface plate. If a pushrod is not straight, it will appear to hop as it’s rolled. However, the most accurate way to check for straightness is by using a dial indicator.

Camshaft and Bearings --The camshafts in most OHC engines are secured to the cylinder head by bearing caps. Some ride on split bearings, whereas others ride on a machined surface in the cylinder head. The bearings or bearing surface should be carefully inspected for signs of unusual wear that may indicate an oiling or bore alignment problem. If the engine is equipped with camshaft bearings, they are normally replaced during engine rebuilding. If the camshaft bore is damaged, the cylinder head is normally replaced.

Each lobe of the camshaft should be checked for wear, scoring, scuffing, fractured surface, pitting, and signs of abnormal wear. Also check for plugged oil passages.

The camshaft should also be checked for straightness. Place the camshaft on V-blocks. Place a dial indicator on one the middle journals. Rotate the cam shaft and watch the dial indicator (53). Compare the highest reading to specifications. If the measurement exceeds specifications, replace the camshaft. With a micrometer, measure the height of each cam lobe and the diameter of each journal. If the readings don’t meet specifications, replace the cam shaft. Repeat this procedure on each camshaft.

Fgr__53 Camshafts should be checked for straightness. Rotate camshaft while measuring.

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