- Remove the head(s), and place on a clean surface.
- Using a suitable spring compressor (for pushrod-type overhead valve engines), compress the valve spring and remove the valve spring cap key. Release the spring compressor and remove the valve spring and cap (and valve rotator on some engines).
Use care in removing the keys; they are easily lost.
- Remove the valve seals from the intake valve guides. Throw these old seals away, as you'll be installing new seals during reassembly.
- Slide the valves out of the head from the combustion chamber side.
- Make a holder for the valves out of a piece of wood or cardboard, as outlined for the pushrods in "Cylinder Head Removal." Make sure you number each hole in the cardboard to keep the valves in proper order. Slide the valves out of the head from the combustion chamber side; they MUST be installed as they were removed.
Inspect the valve faces and seats (in the head) for pits, burned spots and other evidence of poor seating. If a valve face is in such bad shape that the head of the valve must be ground in order to true up the face, discard the valve because the sharp edge will run too hot. The correct angle for valve faces is 45 degrees. We recommend the re-facing be done at a reputable machine shop.
Check the valve stem for scoring and burned spots. If not noticeably scored or damaged, clean the valve stem with solvent to remove all gum and varnish. Clean the valve guides using solvent and an expanding wire-type valve guide cleaner. If you have access to a dial indicator for measuring valve stem-to-guide clearance, mount it so that the stem of the indicator is at 90° to the valve stem, and as close to the valve guide as possible. Move the valve off its seat, and measure the valve guide-to-stem clearance by rocking the stem back and forth to actuate the dial indicator. Measure the valve stems using a micrometer, and compare to specifications to determine whether stem or guide wear is responsible for the excess clearance. If a dial indicator and micrometer are not available to you, take your cylinder head and valves to a reputable machine shop for inspection.
Some of the engines covered in this guide are equipped with valve rotators, which double as valve spring caps. In normal operation the rotators put a certain degree of wear on the tip of the valve stem; this wear appears as concentric rings on the stem tip. However, if the rotator is not working properly, the wear may appear as straight notches or "X" patterns across the valve stem tip. Whenever the valves are removed from the cylinder head, the tips should be inspected for improper pattern, which could indicate valve rotator problems. Valve stem tips will have to be ground flat if rotator patterns are severe.
LAPPING THE VALVES
After machine work has been performed on the valves, it may be necessary to lap the valve to assure proper contact. For this, you should first contact your machine shop to determine if lapping is necessary. Some machine shops will perform this for you as part of the service, but the precision machining which is available today often makes lapping unnecessary. Additionally, the hardened valves/seats used in modern automobiles may make lapping difficult or impossible. If your machine shop recommends that you lap the valves, proceed as follows:
- Invert the cylinder head so that the combustion chambers are facing up.
- Lightly lubricate the valve stems with clean oil, and coat the valve seats with valve grinding compound. Install the valves in the head as numbered.
- Attach the suction cup of a valve lapping tool to a valve head. You'll probably have to moisten the cup to securely attach the tool to the valve.
- Rotate the tool between the palms, changing position and lifting the tool often to prevent grooving. Lap the valve until a smooth, polished seat is evident (you may have to add a bit more compound after some lapping is done).
- Remove the valve and tool, and remove ALL traces of grinding compound with solvent-soaked rag, or rinse the head with solvent.
Valve lapping can also be done by fastening a suction cup to a piece of drill rod in a hand "eggbeater" type drill. Proceed as above, using the drill as a lapping tool. Due to the higher speeds involved when using the hand drill, care must be exercised to avoid grooving the seat. Lift the tool and change direction of rotation often.
The engines covered in this guide use integral valve guides; that is, they are a part of the cylinder head and cannot be replaced. The guides can, however, be reamed oversize if they are found to be worn past an acceptable limit. Occasionally, a valve guide bore will be oversize as manufactured. These are marked on the inboard side of the cylinder heads on the machined surface just above the intake manifold.
If the guides must be reamed (this service is available at most machine shops), then valves with oversize stems must be fitted. Valves are usually available in 0.001, 0.003 and 0.005 in. stem oversizes. Valve guides which are not excessively worn or distorted may, in some cases, be knurled rather than reamed. Knurling is a process in which the metal on the valve guide bore is displaced and raised, thereby reducing clearance. Knurling also provides excellent oil control. The option of knurling rather than reaming valve guides should be discussed with a reputable machinist or engine specialist.
Height and Pressure Check
- Place the valve spring on a flat, clean surface next to a square.
- Measure the height of the spring, and rotate it against the edge of the square to measure distortion (out-of-roundness). If spring height varies between springs by more than 1 / 16 in. or if the distortion exceeds 1 / 16 in. replace the spring.
A valve spring tester is needed to test spring test pressure, so the valve springs must usually be taken to a professional machine shop for this test. Spring pressure at the installed and compressed heights is checked, and a tolerance of plus or minus 5 lbs. (plus or minus 1 lb. on the 231 V6) is permissible on the springs covered in this guide.
New valve seals must be installed when the valve train is put back together. Certain seals slip over the valve stem and guide boss, while others require that the boss be machined. In some applications, Teflon guide seals are available. Check with a machinist and/or automotive parts store for a suggestion on the proper seals to use.
Remember that when installing valve seals, a small amount of oil is able to pass the seal to lubricate the valve guides; otherwise, excessive wear will result.
To install the valves and rocker assembly:
- Lubricate the valve stems with clean engine oil.
- Install the valves in the cylinder head, one at a time, as numbered.
- Lubricate and position the seals and valve springs, again a valve at a time.
- Install the spring retainers, and compress the springs.
- With the valve key groove exposed above the compressed valve spring, wipe some wheel bearing grease around the groove. This will retain the keys as you release the spring compressor.
- Using needlenose pliers (or your fingers), place the keys in the key grooves. The grease should hold the keys in place. Slowly release the spring compressor; the valve cap or rotator will raise up as the compressor is released, retaining the keys.
- Install the rocker assembly, and install the cylinder head(s).
All engines in this guide use hydraulic valve lifters, which require no periodic maintenance or adjustment. However, in the event of cylinder head removal or any operation that requires disturbing or removing the rocker arms, the rocker arms have to be adjusted.151 Four and 250 Inline Six Cylinder Engines
- After rocker arm or cylinder head disassembly, proceed as follows:
- Remove the valve cover if it is not already removed.
- Remove the distributor cap and crank the engine until the rotor points at number one plug terminal in the cap. It is easier to do this if you mark the location of number one plug wire before you remove the cap. The points should be open (1974 250 six) and timing marks should be aligned. (the 0° mark on the timing tab). Number one cylinder should now be at TDC.
- With the number one cylinder of the 250 six in this position, adjust: Intake valves 1,2,4, and exhaust valves 1,3,5 (numbered from the front of the engine). On the 151 four cylinder, adjust valves 1,2,3 and 5 (counting from the front of the engine). The adjustment is performed as follows: Turn the adjusting nut until all lash is removed from this particular valve train. This is determined by checking pushrod sideplay while turning the adjusting nut. When all play has been removed, turn the adjusting nut one more turn. This will place the lifter plunger in the center of its travel.
- Crank the 250 six engine over through one complete revolution until number six cylinder is in the firing (TDC, timing pointer at 0°) position. Crank the 151 four through one complete revolution until number four cylinder is in the firing position. At this point, you can adjust the following valves on the 250 six: Intake valves 3,5, and 6; exhaust valves 2,4 and 6. On the 151 four, adjust valves 4,6,7 and 8 in the same manner.
- After the engine is running, readjust the valves following the procedure under "Engine Running." Install the valve covers using new gaskets or sealer.
- Run the engine until normal operating temperature is attained. Remove the valve cover. To prevent oil splashing, install oil deflector clips, which are available at auto supply stores.
- With the engine at idle, back off the rocker arm nut until the rocker arm begins to clatter.
- Slowly tighten the rocker arm nut until the clatter just stops. This is zero lash.
- Tighten the nut another quarter turn and then wait about ten seconds until the engine is running smoothly. Tighten the nut another quarter turn and wait another ten seconds. Repeat the procedure until the nut has been turned down one full turn from zero lash.
Pausing ten seconds each time allows the lifter to adjust itself. Failing to pause might cause interference between the intake valve and the piston top causing internal damage and bent pushrods.
- Adjust the remaining valves in the same manner.
- Replace the valve cover.
- Remove the valve covers and crank the engine until the mark on the damper aligns with the TDC or 0° mark on the timing tab and the engine is in the No. 1 firing position. This can be determined by placing the fingers on the No. 1 cylinder valves as the marks align. If the valves do not move, it is in the No. 1 firing position. If the valves move, it is in the No. 6 firing position (No. 4 on V6) and the crankshaft should be rotated one more revolution to the No. 1 firing position.
- Back out the adjusting nut until lash is felt at the pushrod, then turn the adjusting nut in until all lash is removed. This can be determined by checking pushrod end-play while turning the adjusting nut. When all play has been removed, turn the adjusting nut in 1 full turn.
With the engine in the No. 1 firing position, the following valves can be adjusted:
Crank the engine 1 full revolution until the marks are again in alignment. This is the No. 6 (No. 4 on V6) firing position. The following valves can now be adjusted:
- Install the valve covers using new gaskets or sealer as required.