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It is unlikely that the timing gear has jumped a tooth or two. But there is an easy way to check without taking the engine apart. First a little theory. The piston is at top dead center (TDC) for two times during the 4 stroke cycle. The first time the fuel is igniting and pushing down on the piston to start the power stroke. The second time the cylinder is switching from the exhaust stroke to the intake stroke. At that TDC both valves are slightly open.
The timing detent in the timing gear on the camshaft is used to locate TCD for the power stroke for the #1 cylinder. At the same time the #4 piston is at TCD switching from the exhaust stroke to the intake stroke.
Take all the plugs out. Leave the ignition and fuel off. Rotate the engine until the timing pin drops into the detent in the camshaft timing gear. Use a bore scope or other tool to check that the #1 piston is at TDC. The timing can be off a few degrees and the piston will still look like it is at TDC. Now check the valves on the #4 cylinder. The both should be just slightly open. If the cam timing is off, one valve will be closed and the other will be open about 1/4 inch.
The timing gears are helical cut, not straight cut, so I guess it is possible for the timing to change if the cam shaft is moving forward. If the cam plunger and spring are completely missing then I guess the timing could change to the point where the engine performance would be compromised.