The main faults of the gas distribution mechanism are: violation of the thermal gaps of the valves; Pulling of the toothed belt, wear of the toothed pulleys; Wear of a chain and asterisks of a drive; Weakening of the camshaft bearing cap fasteners, loose valve closing due to wear of their heads and saddles; Reducing the elasticity of the valve springs, wear of bearings, necks and cams of the camshaft, pushers, pistons and their axles, bushings and valve seats.
As a result of violation of adjustments and wear of the parts of the gas distribution mechanism, knocking and noise are heard while the engine is running, it loses power, there is an increased oil consumption, etc. After checking the technical condition, it is necessary to repair or adjust the timing mechanism.
The camshaft and its drive. The main malfunctions are the wear of the shaft journal bearings, the wear and tear of the cams and the bending of the shaft. These damages cause knocking in the valve mechanism, and an increase in clearance in the bearings leads to a drop in oil pressure in the lubrication system.
To restore the clearances in the bearings of the camshaft, rebuild and grind its supporting necks, the oil grooves are deepened, so that after repeated grinding, oil is supplied to the engine parts. Shaft shafts are ground to the nearest repair size. After grinding, they are polished with GOI paste.
When the cams of the camshaft are slightly worn out, they are sanded with a sanding cloth, first coarse, then fine-grained. The places of metal dying at the ends of the tops of the cams are filed with a grinding bar or emery cloth until the sharp edges are eliminated. When discarding more than 3 mm along the length of the cam, the shaft must be replaced. If cams of a camshaft are worn on height, they grind on a special copy-grinding machine for camshafts. The cams of the shaft, having considerable wear, can be restored by surfacing with subsequent grinding.
After repair, the shaft is washed and the height of the jaws is checked. When the cams are worn over the height by more than 0.5 mm in comparison with the nominal height, the shaft is replaced, since with this deterioration the filling of the cylinders deteriorates, resulting in the engine power dropping.
If the support neck of the camshaft is worn over the permissible limits, they are restored by surfacing, by remaining or chrome plating, and then ground.
The bend of the camshaft is measured with a special indicator and checked on the middle neck. The allowable bending (beating) can be no more than 0.10 mm. If it is more, you need to edit the shaft.
On the bearing surfaces, there should be no scratches and gaps under the shaft journals, and there should be no cracks on the bearing housings. After cleaning and washing the camshaft, check the clearance between its necks and the holes of the supports on the cylinder head. In order to determine the clearance, it is necessary to measure the diameter of the camshaft neck, install the bearing corresponding to it, fix its housing and measure the bearing inside diameter, then subtract the second value from the first. The difference in values is the size of the gap. Measure the gap and the calibrated plastic wire. The permissible clearance can not be more than 0.2 mm.