What Is The Valve Clearance On A 4-Stroke Engine?

Setting the valves on a 4-stroke engine.


From time to time on 4-stroke scooters, it is necessary to adjust the valves.

Do it yourself, or in the service, everyone decides for himself. I want to note that adjusting the valves is not such a tricky thing; anyone who knows how to turn the nuts can handle it. This process takes 20-30 minutes. Only attention and accuracy are needed.

When it is necessary to adjust?

Most often, reduced or increased clearance in the valves leads to the fact that:


After removal, make sure that no foreign objects get into the engine.

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Step 1. Fan cover

To adjust the valve, we must find the top dead center (V.M.T.) piston. To do this, remove the plastic lining of the fan for the generator:

Turn off the 2 nuts (M8) and two screws and remove the lining:

Step 2. Cylinder head cover

Remove the cylinder head valve cover:

To do this, unscrew 4 M10 nuts and 2 nuts (bolted crankcase tube nuts).

Step 3. Top Dead Point

V.M.T. is the point at which the piston in the cylinder occupies the upper position. This article discusses the V.M.T. search method using tags on the generator rotor.

Four-stroke scooters have 2 M.T.! (upper and lower)

There are 3 holes on the camshaft gear. Their arrangement shown in the photo corresponds to the V.M. of the piston, in which both valves are completely closed (what we need).

On the generator flywheel, there are risks: T (V.M.T.) and F (ignition moment):

Risk T must be opposite the protrusion indicated in figure 1.

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To combine the protrusion and the risk T, it is necessary to rotate the engine CLOCKWARE using the socket wrench. To find out that this is V.M.T., gently move the key, while the rocker arms of the valves should not move. If they move, then it’s not V.M.T., turning the fan further, CLOCKWISE until the risk and the protrusion are combined.

Well, the top dead center is found, now you can begin to adjust the valves.

Step 4. Adjusting / Checking valve clearance.

To check the gap, take the gauge 0, 05 mm and try to push it between the inlet valve and the adjusting bolt.

If this fails (due to the lack of or too small a gap) or the gap is too large, then loosen the lock nut M9 and twist the pliers or a suitable key with a tuning bolt. Clockwise. the gap decreases, counterclockwise. increases. At the same time, keep the gauge between the valve and the adjusting bolt.

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The probe should sit tightly between them so that the examination can move, but when moving, the probe should not be wedged (i.e., the probe should be pressed a little with the adjusting bolt). Tighten the locknut, holding the adjustment bolt with a key or pliers. After tightening, we control the gap again.

The inlet valve is set.

Do the same with the release valve. Access by the probe to it is difficult but possible. The gap there should be 0, 1 mm.

With setting valves complete. Reassemble in reverse order, put all the parts on