Using a valve spring compressor such as those used on overhead valve automotive engines, remove the valve springs, valve washers, (valve stem seal set, intake only and valves from the cylinder.
Clean the valves with a wire-wheel brush. All carbon must be removed from the top and bottom of the head. Do not overlook the varnish which might have accumulated on the stem.
In refacing valves, take off only the minimum of metal required to clean up the valve faces. If the outer edge of the valve becomes too thin or sharp due to excessive grinding, the valve must be replaced. The valve head margin must be at least 3/64″. This margin is the area above the contact surface of the valve face. See figure 14.
Inspect the valve seats in the combustion chamber for cracks, burns, pitting, ridges or improper angle. If any of the above conditions are noted, the seats must be reground. NOTE: Valve seats are permanently installed and cannot be replaced. Therefore, a minimum of metal should be removed when grinding the valve seats.
The valve seat width after refacing should be a liberal 1/16″ for intake seats, but not more than 3/32″ in any case. The width of exhaust seats should be 3/64″ to 1/16″.
Test valve for concentricity with seat and also for tight seating. Valves can be tested by coating the valve face with Prussian Blue and turning the value against its seat. This indicates whether the seat in concentric with the valve guide, but does not prove that the valve face is concentric with the valve stem, or that the valve is seating all around.
After making this test, wash all blue from the surfaces, lightly coat the valve seat with blue and repeat the test to see whether a full mark is obtained on the valve. Both tests are necessary to prove that a proper seat is being obtained.
Excessive clearance between valve stems and guides will cause improper seating and burned valves. When there is too much clearance between intake valve stems and guides, there is a tendency to draw oil vapor through the guide on the suction stroke, causing excessive oil consumption, fouled spark plugs and poor low speed performance.
If the valve guides are to be replaced, the old guides should be pressed out with an Arbor Press and new guides pressed in. The intake guide should be so positioned that it will extend 1/64″ above the guide boss.
This is to allow the valve seal washer to be properly seated. After the new guides have been pressed into the bosses, they must be sized with a hand reamer to between .3115 and .3125. Although the inside diameter of both valve guides are the same, the stem clearance of the exhaust valve is different than that of the stem clearance of the intake valve. Due to the fact that the diameter of the exhaust valve stem and the intake valve stem are as follows:
NOTE: Valve guide reamer Part No. 111275
Exhaust valve stem diameter .3110 to .3093 Clearance .0032 to .0015
Intake Valve stem diameter .3110 to .3103 Clearance .0022 to .0005
NOTE: It is essential that the valve seats be refaced after new guides are installed.
The intake valve only utilizes a valve stem seal set, which consists of a neoprene gasket, a Teflon lip seal and a hold-down spring. See figure 154. Never attempt to re-use the above mentioned seals.
Place the flat neoprene gasket over the valve stem on the top of the valve guide.
With the Teflon lip seal thoroughly oiled, position the seal over the valve stem with the flat side toward the cylinder. Extreme caution must be exercised when installing the lip seal over the valve stem to avoid andy damage to the seal by the valve stem grooves. A plastic installer is provided for seal protection.
Place the hold-down spring on the lip seal assembly, being sure the spring seats properly on the sseal body. Install intake valve spring, retainer and keepers.
It is possible to install these seals without removing the cylinder from the engine. Remove the spark plug and in its place install an air plug valve holder to which an air line can be attached.
The air pressure in the cylinder will hold the valve tight against its seat, making it possible to remove the valve spring using a lever type valve spring compressor, without losing the valves in the cylinder.
Lever type valve spring compressosrs and air plug valve holders are available through automotive suppliers.
When new rings are installed without reboring cylinder the glazed cylinder walls should be slightly dulle, but without increasing the bore diameter. This is done with a “glaze-buster” or with a hone equipped with the finest grade of stones.
Using an inside micrometer, check the cylinder for a taper or out of round condition, a cylinder with more than .005 out of round should be rebored, and proper oversize piston and rings used. Following are the dimensions that the cylinder should be bored for a given oversize:
Oversize Cylinder Diameter
Honing the cylinder after reboring is necessary to remove machine marks left by the boring tool. Approximately .001 to .0015 of metal should be removed from the cylinder bore with the hone, using a 150 grit stone.
This will leave a 25 to 35 RMS micro inch finish to the surface of the cylinder. Allowances must be made for the honing operation when the cylinder is bored, so that after honing, the cylinder will be the correct size. The cyinder bore should then be scrubbed, using a stiff bristle brush, warm water and soap suds, to loosen any metal particles left by the honing operation. Wash with clean water, and dry thoroughly to prevent any rust from forming.
If through continued use, the spark plug hole in the cylinder becomes damaged, or the threads stripped, it is possible to repair the damaged threads by installing a Heli-Coil.
We recommend an AC-C85 spark plug for use with a Heli-Coil. This is a gasketed plug; under no circumstances should a tapered seat plug be used with a Heli-Coil, as the tapered seat in the cylinder is removed when the Heli-Coil is installed.
Cushman Motors does not offer the Heli-Coil repair kit, as it is generally available through automotive suppliers.
Fit a new “O” ring around the outside diameter of the oil return tube and push it down until it bottoms against the lip. Install the oil return tube through the ridge of the cylinder and up through the fins. With a new gasket in position on the cylinder and a new “O” ring fitted to the oil drain block, secure drain block to cylinder with the proper screws and at the same time, position oil drain tube into oil drain block.
Thoroughly lubricate the piston rings on the piston and install the ring compressor. Install the cylinder gasket. Slide the piston into the cylinder until all three rings have entered the cylinder bore, See figure 16.
Remove the ring compressor. Install the cylinder retaining lock nuts with flat washers and tighten to the proper torque. Check the specification section of this manual for proper torque values. Install the cam followers and push rod tubes. Use only new “O” rings, and be certain they are in position before making installation fo the tubes. Install new “O” rings on each end of the oil supply tube. Make certain that the oil supply tube hole in the crankcase is free of obstructions and does not contain an old “O” ring. Insert the oil supply tube through the hole in the valve cover base and into the supply hole of the crankcase. Position the oil supply tube housing retainer and secure with the proper screw.
Install the push rods with the cup ends up. Assemble the rocker arm assembly to the cylinder and install the mounting hardware in the reverse manner of which it was removed. See figure 17. The ball end of the rocker arm must fit into the cup of the push rod. Do not install the valve covers at this time.