Saturday, June 11, 2011

Cylinders boring

Figure 5.14
With the cutter set to make the desired cut, the spindle is brought down to the top of the cylinder block and the machine is started. The boring bar with the cutter will feed itself slowly down the cylinder, cutting as it goes (Figure 5.14). When it reaches the bottom of the cylinder, cutting will stop.
During the cut, the
cats paws are extended against the cylinder to support the end of the bar and keep it cutting true.

Honing after boring
The cylinders are bored slightly under-size to allow for honing. The cutter of the boring bar leaves a series of fine ridges in the new bore that are not a suitable surface for piston rings. Honing after boring finishes the cylinder to size and gives it a cross-hatch pattern.

Servicing cylinder sleeves
The three types of sleeves used in engines are dry sleeves, dry flanged sleeves and wet sleeves. Each has a different method of installation.
Sleeves must be installed correctly; otherwise the cylinder bores will be distorted. This can reduce piston clearance and cause scoring of the piston and cylinder. Also, the piston rings will not follow the distorted bore, and this will cause blowby and oil burning.
The way in which the different sleeves are installed is covered briefly under the headings that follow.

Figure 5.15
Installing dry sleeves
Dry repair sleeves are used to recondition badly worn or damaged cylinders that cannot be re-bored without removing excess metal. The cylinder is bored to suit the outside diameter of the sleeve which is pressed into the block (Figure 5.15). After installation, the inside of the sleeve is finished to standard size.
The brief procedure for installing a sleeve is as follows:
I. Bore the cylinder to the outside diameter of the sleeve — provide for a 0.08 to 0.10 mm press fit.
2. Measure the length of the bore and cut the sleeve so that it is about 3 mm longer.
3. Shrink the sleeve with dry ice to ease installation and press it into place. Then finish the top of the sleeve flush with the top of the block.
4. Bore the sleeve slightly smaller than the final diameter and hone it to size.

Installing flanged dry sleeves
Dry replacement sleeves have a flange that holds them in place. They do not fit as tightly in the cylinder block as dry repair sleeves.
1. Clean the bore in the block and check for distortion. Clean the counter-bore at the top of the block and check for size. The bore should be measured at several places.
2. Wash the outer surface of the sleeve with solvent to remove any dirt or protective coating.
3. Install the sleeve in the cylinder. If it is the correct fit, it should be possible to press the sleeve two- thirds of the way in with hand pressure.
4. Press the sleeve the rest of the way into the block, and check the distance that it protrudes above the top of the block. A general rule is for the flange to protrude 0.02 to 0.12 mm above the top of the block.
. Compare the protrusion of adjacent sleeves. There should be no more than 0.02 mm difference.

·           If there is too much protrusion the cylinder-head gasket will not he able to seal properly.

Installing wet sleeves
Figure 5.16
Because a wet sleeve is in contact with the engine coolant, its fit and scaling in the cylinder block are important. All rust and scale must be removed from the block counter-bore and the sealing-ring area. The new sleeve should be washed in solvent before it is installed.
Some brief points about installation are:
I. Try the sleeve in the block bore before installing the sealing rings — it should fit freely without binding.
2. Check the protrusion above the block. Hold-down clamps can be used to keep the sleeve seated (Figure 5.16).
3. Remove the sleeve from the block and install the sealing rings. Lubricate the sealing rings with lubricating oil or grease.
4. Install the sleeve in the bore so that it seats against the counter bore. A sleeve driver is used, or a piece of wood is placed over the sleeve, and the sleeve is tapped into place with a hammer.
When the sleeve has been installed, the piston (without rings) should be inserted and moved the full length of the sleeve to check for distortion. The piston should have the same clearance and slide freely for the full length of the bore.

Figure 5.17
Removing cylinder sleeves
If a thin dry sleeve has to be removed, then it could be bored out. The boring bar is mounted a little to the side of the cylinder so that it cuts away the side of the sleeve, but not the block. This relieves the interference fit between the sleeve and the cylinder block so that the sleeve can be removed.
Replaceable dry sleeves and wet sleeves can be removed and installed with a sleeve puller (Figure 5.17). Wet sleeves arc easier to remove than dry sleeves.

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