Ural M-72 Valve Gear

Valve gear

The engine relies to a great extent on correct adjustment of the valve gear in order to run normally.

Correct clearances are a vital precondition if maximum power output is to be achieved. The gap between pushrod and valve stem should be adjusted after the valves have been lapped in. The size of the gap should be checked after every 313 – 625 miles (500 –1000 km) of travel.

valvegear

fig. 9. valve gear:
1 – valve; 2 – valve spring; 3 – valve spring seat; 4 – collet; 5 – cam follower; 6 – push rod;
7 – adjustment bolt; 8 – locknut; 9 – tappet cover; 10 – gasket; 11 – screw.

Use the following method to adjust the clearance:

1. Undo screw 11 (fig. 9) and remove the tappet cover along with its gasket.

2. Rotate the crankshaft until the inlet valve closes (there should be a pronounced gap between the pushrod and the inlet valve stem). Adjust the exhaust valve clearance in this position. Next, continue to rotate the crank shaft until the exhaust valve begins to rise. Set the inlet valve clearance.

To adjust the clearance, slacken locknut 8 and turn pushrod adjustment bolt 7 to increase or decrease the clearance as required. Tighten the locknut.

The clearance should be adjusted on a cold engine. The gap should be 0.1 mm. If there is only a very small gap, or none, the valve will not seal tightly on its seat when closed.

When forced to dismantle and re-assemble the engine, the valve gear timing can be correctly set by aligning the marks on the crankshaft and camshaft gears (fig. 10).

camshaft

fig. 10 The camshaft assembly.
1 – camshaft; 2 – crankshaft gear; 3 – camshaft gear; 4 – generator gear; 5 – ignition cam; 6 – crankcase breather;

After 4689-5000 miles (7500-8000 km), the valves should be lapped in and the carbon deposits on the cylinders and pistons should be removed.