On all engines, the cylinder head must be removed from the vehicle and the camshaft(s) and rockers removed from the head.Valves and components must be reinstalled in their original positions. Develop a system to store and identify parts as they are removed. Identify components by location and application (Example: Cyl. 2 exhaust) to avoid confusion. Keep the work area clean and store small parts immediately.The use of the correct special tools or their equivalents may be required for some procedures.
See Figures 1, 2, 3 and 4
The early Mitsubishi engine use a small "jet valve" next to the main intake valve. This small additional valve directs a portion of the air/fuel mixture at the spark plug, allowing hotter and more complete combustion. The jet valve must be removed before removing the larger valves.
The jet valve assembly is screwed into the head. The use of special tool (socket) MD 998310 is required to remove and install the valve. When using the tool, make certain that the wrench is not tilted with respect to the center of the valve. If the wrench is tilted, the excess pressure on the spring retainer may bend the valve stem, causing it to bind during operation. Remove the assembly and set it aside.
On all heads, install a standard valve spring compressor and tighten it to compress the spring. Remove the valve spring retainers (collets) from the valve stem. A small magnet can be very helpful for this. Slowly loosen the spring compressor and remove the valve spring retainer, the spring and the lower spring washer (spring seat). The valve can now be withdrawn from the combustion side of the head. Use a pair of pliers to remove the valve stem seal from each position. Discard the seals immediately; they cannot be reused.
Each valve should be cleaned to remove the carbon deposits from the valve head and stem. This may be done either with chemical cleaners (wear eye protection and gloves) or with the wire brush and power drill used to clean the head. Do not use sandpaper or other abrasives to clean the valves.
See Figures 5, 6, 7, 8, 9 and 10
Inspect each valve for burning of the head or deformation of the lower stem. Severe corrosion, pitting, burning, or cracking of these parts mean the valve must be replaced. Inspect the top of the stem for pitting. If the pitting is light and the valve is otherwise in good condition, pitting may be removed by light application of an oil stone.
Measure the stem diameter at several points along its length. A common wear point is just above the head of the valve where the stem enters the valve guide. If this area is worn, the valve must be replaced. Visually check the top of the stem for mushrooming or deformation and replace the valve if any such damage is found.
Inspect the valve margin for adequate thickness. This is the vertical section of the valve head below the seating surface. The margin is just that-a thickness of metal giving strength to the valve head.
Measure the height of valve springs. This height (or free length) is an indicator of the strength and condition of the spring. A worn spring will compress but not return to its full length. This may allow the valve to stay partially open, causing driveability problems.
Check each spring for squareness by placing the side of the spring next to a T-square and rotating the spring until you find maximum out-of-square. Squareness is measured in degrees and without very accurate measuring equipment, you won't be able to put a number on the error. Suffice it to say that if any out of square is detected, the spring should be replaced. A very slight deviation is acceptable (the limit is 2°) but this is so small an angle that you may not even notice it.
Measure stem-to-guide clearance. Depending on the tools available, either measure the valve stem and the valve guide individually, then subtract to find the clearance or install the valve in its guide and locating a securely mounted dial indicator against the top of the stem. Rock the valve away from the indicator and hold it there while you zero the indicator. Then rock the valve all the way toward the indicator and hold it there as you take the reading. If the stem-to-guide clearance exceeds specifications the valve and/or guide should be replaced.
The valve face and seat surfaces must have consistent contact near the center of each. Coat the surface of the seat with a metal dye (such as Prussian blue) or a thin coat of lapping compound. Insert the valve all the way so the marking material is transferred to the valve face. If a consistent mark is found toward the center of the valve face all around, the valve and seat may be re-used as is, assuming there are no other problems with the valve. If the seating is questionable or obviously bad, the valve and seat should be machined to the proper dimensions and angles by an automotive machine shop.
It then must be lapped in (polished) by coating the seating surfaces with a lapping compound and rotating the valve with a special suction cup tool until the surfaces mate perfectly; lapping compound must then be thoroughly cleaned from both surfaces.Jet Valve Service
See Figures 11, 12, 13 and 14
While the jet valve is replaced as an assembly rather than being serviced, you can disassemble it to inspect it and replace the valve stem seal. You should use tool MD 998309 or equivalent.
- Disassemble the jet valve with the special tool used as a spring compressor. The forked portion of the tool fits over the ridge at the center of the assembly while the hole in the upper section fits over the valve stem. Compress the spring enough to remove the keepers and remove them; then slowly release the pressure.
- Disassemble each jet valve assembly so all parts are kept together. Check the seat and valve faces for any signs of burning or cracks. Make sure the valve slides in the jet body smoothly and without play. If there are any signs of burning or excessive valve stem wear, the jet valve assembly must be replaced. Inspect the spring for cracks of any kind, and replace defective springs.
- Coat the valve stem with clean engine oil and insert it into the jet valve body. Sit the assembly on a flat surface, place a new seal squarely over the valve stem, and install the seal with the special installation tool, tapping downward on it gently with a hammer. Make sure the valve stem still moves up and down smoothly after the seal is installed; if movement is not smooth, the seal has been damaged or is not installed squarely.
- Install the spring and spring retainer, compress the spring with the special tool and install the keepers, making sure they remain squarely in the valve stem groove until tension is removed and the retainer covers them. If they do not lock in place securely, the valve spring could pop out either as you are working on the engine, or later, when the engine is operating.
- Coat a new O-ring with clean engine oil and coat the threaded area and sealing areas of the jet body. Install the new O-ring into the groove provided for it. Then, insert each jet valve squarely into the hole in the cylinder head and start the threads carefully. Use the special socket and a torque wrench to tighten the assembly to 13-15 ft. lbs. (18-20 Nm) keeping the wrench square to the valve stem at all times.
See Figure 15
Before reassembly, check that all lapping compound has been cleaned from the head. Remember that each piece being reused must be reinstalled in its original position.
- Position the spring seat on the head. The seat will be forced into its final position in the next step.
- Install the valve stem seals and insure proper installation of the spring seats.
- Thoroughly coat the valve stem with clean engine oil. Insert the valve slowly from underneath, guiding it gently through the new seal. Make sure the valve will slide up and down smoothly, indicating the seal is in proper position.
- Install the valve springs with the color-coded end facing upward. Install the retainer on top of the spring. Compress the retainer with the valve spring compressor until the retainer sits below the groove in the valve stem.
- Install the keepers, making sure they stay properly positioned in the stem groove, and release the tension on the compressor slowly. Note that if the keepers do not sit squarely in the grooves, the valve spring tension could be released suddenly either as you work, or later as the vehicle is in operation. Once the keepers have locked securely, remove the valve spring compressor.
- Repeat the sequence for each intake and exhaust valve.
After valve spring assembly installation tap the top of the valve springs to make sure the valve keepers are seated properly.