To check and adjust the valve clearances, remove the cylinder head cover (see "Cylinder head - removal and installation").
Attention! Checking the thermal clearances of the valves is performed on a cold engine (temperature not higher than 30°C).
The size of thermal gaps is checked with flat feeler gauges.
I. Using a 10 mm Allen key, unscrew the plug of the right crankcase cover.
Attention! The crankshaft may only be rotated in the direction of engine operation (clockwise).
2. Using a 14 mm socket wrench, rotate the crankshaft by the generator rotor bolt until the drive cam of the valve being measured is in the "closed" position. The gap A is measured between the tappet and the cam in the position where the cam does not interact with the tappet (the valve is closed).
3. Measure the gap. The gap corresponds to the nominal value of the feeler gauge if the feeler gauge moves between the shaft cam and the pusher with some effort (the feeler gauge "falls through" - the gap is larger, enters with excessive effort - the gap is less than the nominal value of the feeler gauge).
The nominal clearance for the intake valves is 0.15±0.03 mm.
The nominal clearance for exhaust valves is 0.22±0.03 mm.
4. Record the clearance values for each valve.
5. If the clearances are within the permissible values, the work can be considered complete. If the clearance of any valve has gone beyond the specified values, it is subject to adjustment. The Honda CB400SF motorcycle uses a scheme for adjusting the thermal clearances of the valves using adjusting washers of different thicknesses. The change in the thermal clearance of the valve occurs due to the gradual wear of all parts of the valve mechanism. Adjusting washers of different thicknesses compensate for an excessively large or small clearance, changing the overall height of the valve-pusher unit.
Attention! When removing the tappets, it is important not to mix them up. It is most convenient to lay them out on a clean cloth or paper in the order they were installed in the engine and label them.
6. Remove the camshafts and extract the tappets from the cylinder head sockets (see "Cylinder head - removal and installation").
7. Remove the adjusting washers.
Attention! As a rule, the washers are removed together with the tappets, sticking to them on a layer of oil, but it also happens that the adjusting washer remains in the seat of the valve spring plate. In this case, we remove the washer with a magnet or tweezers.
Attention! When calculating the thickness of a new washer, do not take into account the thickness indicated on the surface of the old washer. The fact is that during operation, the thickness of the washer decreases and becomes less than the value indicated in the marking.
8. Using a micrometer, measure the actual thickness of the washer.
We calculate the thickness of the new washer using the formula A = B + (C - 0.15) - for intake valves, A = B + (C - 0.22) - for exhaust valves, where A is the thickness of the required washer, B is the thickness of the old washer, C is the measured thermal clearance.
Example
If the measured clearance on the intake valve is 0.20 mm, and the thickness of the installed washer is 1.850 mm, then the thickness of the new washer should be 1.90 mm: 1.85 + (0,20 - 0,15) = 1.90. We select the closest washer in thickness, i.e. 1.900 mm. As a result, the thermal clearance in the valve will be 0.15 mm.
The manufacturer produces 65 sizes of washers with a thickness from 1.200 mm to 2.800 mm with a step of 0.025 mm - 1.200-1.225-1.250-1.275-1.300, etc.
The thickness of the washer is applied to one of its sides using an electrographic method.
9. Install a new washer into the valve plate seat.
10. Install the pusher in place.
11. Repeat steps 7-9 for all other valves.
12. Install the camshafts, camshaft plain bearing caps and tighten their mounting bolts to the specified force (see "Cylinder head - removal and installation").
13. Using a 14 mm socket wrench, turn the engine crankshaft 3-4 turns, check again using the marks to see if the timing phases are set correctly, and check the valve mechanism thermal clearances once again.
14. We carry out further assembly of the engine in the reverse order (see "Cylinder head - removal and installation").