105407-4740 ZEXEL 9 420 612 855 BOSCH GOVERNOR 9420612855 1054074740 1157705640

Checking The Piston
1. If the cylinder is renewed, a new piston must be fitted. Normal and oversizes are given in the specifications.2. Inspect the piston for damage or visible wear, including the bosses.
3-613. Remove the compression rings and bevelled scraper ring. (Use piston-ring expander No. 130300)Fig. 3-61
3-624. Open and remove the expander spring for the bevelled scraper ring.Fig. 3-625. Clean the piston-ring grooves.
3-636. Measure axial piston ring clearance by using commercial tools.Fig. 3-63, leftMeasure first piston ring groove, if trapezoidal, by means of trapezoidal groove wear gauge No. 130360.Fig. 3-63, right
3-64 If, when measuring a piston with trapezoidal ring groove, a gap "S" (Fig. 3-64) is found to exist between the inserted gauge and the piston, this means that the axial piston ring clearance is within the tolerances stated in the Specification Data and the piston is fit for further use.
3-65But if the gauge contacts the side of the piston (see Fig. 3-65), i.e. without gap, the piston has to be renewed.
3-667. Insert all the piston rings singly in the cylinder and press down with the piston to a distance of 30 mm from the cylinder head contacting surface. Measure the gap clearance of the piston ring.Fig. 3-668. Compare the gap clearances of the piston rings with the values given in the specifications.9. Renew defective pistons together with gudgeon pin and rings. Renew also cylinders.
3-6710. When installing the piston rings start by fitting the expander spring for the bevelled scraper ring in the bottom groove.Fig. 3-67
3-6811. Assemble the piston rings with the aid of piston-ring expander No. 130300, in the following sequence:No. 3 (No. 4) Slotted, double-chamfered oil-control ring, chromium-plated.(No. 3) Tapered compression ring, ferrox finished; install with face marked "top" upwards.No. 2 Tapered compression ring, ferrox finished; install with face marked "top" upwards.No. 1 Top, double-trapezoidal compression ring, chromium-plated. "top" upwards.Fig. 3-68 Place the rings so that the gaps are evenly spaced around the piston.
3-6912. Check piston pin for wear using a bevelled steel straight edge or measuring angle, Fig. 3-69.
3-70 Secure the opposite end of the gudgeon pin in position. Place the piston on the small end of the connecting rod so that the exhaust air side of the piston (marked on the piston crown) is in the same direction as the open side of the connecting-rod bearing. Press in the gudgeon pin.Fig. 3-70Checking The Connecting Rod
Gauging and replacing piston pin bush
3-711. Set inside micrometer to starting dimension using a micrometer frame (see Technical Data).Fig. 3-71
3-722. Measure the piston pin bush at points one and two in the planes "a" and "b".Fig. 3-72 Attention:Compare recorded values with those specified in the Technical Data.
3-733. Pull out old piston pin bush with fixture No. 131310 and pull in new piston pin bush with the same device.Fig. 3-73
3-74 Note for installation:Pull in the new piston pin bush flush, making sure that the oil bores in bush and connecting rod coincide.Fig. 3-74Gauging And Replacing Big-End Bearings
3-75The big-end bearings are of finished type. They are made of two half