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This manual is intended to make using the S.P.S. Minibar as easy as possible for a new user, and perhaps give a few new tips for others who are familiar with cylinder boring machines in general. Don't be concerned that it includes a spare part list, Minibars seldom ever need any replacement parts, it is simply an easy way of describing the various components and functions of the machine !


The manual is divided into sections covering care and operation of the machine in a basic manner and later on, a section of hints and tips to help you overcome tricky problem jobs and speed up operations whilst at the same time reducing the chance of costly mistakes. These hints and tips are the result of 40 years experience of boring cylinders, so they are well worth reading !






S.P.S. Minibars are designed to work for very many years without the need for any significant overhaul or maintenance. However like any precision instrument, they will perform best when carefully looked after, kept clean and dry and not abused.


As dispatched, the machine is lightly oiled. It is not packed in a preserved, or inhibited state and should not be put into storage. It is ready for use, and during regular use will require no special attention beyond that detailed below. If the machine is to be stored or left unused for a considerable length of time, it will be necessary to inspect and lubricate the external unpainted parts from time to time.


In normal use, the main column and drive shaft should be lubricated daily, also the rack pinion which is provided with a lubricating cup.






Set the table with the long studs pointing downwards and tighten the clamp screw to prevent the table from rotating.


The anchor screw should be screwed into the top face of the table until the underside of the head is level with the machined faces of the bridge platform located at the rear base of the boring machine (this distance is approximately 10mm). Now place the machine on the stand top. Take the hold down shoe (MN7) assembly and slide it into the base of the machine so that anchor screw slots into the shoe. Now turn the hold down screw (MN92) clockwise until the machine is securely clamped down.


The next step is to mount the cylinder on the reverse side of the table. After confirming that the machine is securely fixed to the top of the table, the table clamp screw is slackened to permit the table to be revolved, presenting the cylinder location face and the two long clamping screws uppermost. Using the appropriate spacing ring and packing piece, the cylinder is clamped by the yoke to the table. Try to position the bore as central as possible to the hole in the table, although final centralisation will be performed automatically by the machine later on. One of the knurled clamping nuts has a clutch action to prevent overtightening. Always use this nut in the final tightening action. Obviously, absolute cleanliness is essential in this operation, since any out of squareness in location of the cylinder will result in a bore, which is not true to its axis. Theoretically, all bores should be done "off the base", but in practice, cylinders are almost always have head and base faces which are parallel, so that either face may be used. It is best to avoid removal of studs as far as possible as these can often break or strip threads, leading to unwanted complications.







In the case of motorcar cylinders, (and some V Four type motorcycle types), the stand or table is not used, but the boring machine is clamped directly to the cylinder block, through a cylinder. That is to say the machine is clamped to number 2 cylinder whilst numbers 1 and 3 cylinders are bored, then clamped to number 3 cylinder whilst numbers 2 and 4 cylinders are bored and so on.

Different types of anchor clamp assemblies are available but the standard device is the MN181 type as shown in the parts list. Illustration 1 shows the setup and the procedure is as follows :-

Place the anchor within the cylinder bore, making sure that the toe plate has been securely located and that the parallel sides, or machined parts of the body are contacting the sides of the cylinder walls, noting that the toe plate is adjustable and can be re-positioned to suit various types of cylinder blocks. Expand the cam (MN182) by tightening the adjusting screw (MN184) using the wrench (MN180). When the assembly is securely located, the anchor screw (MN188) should be set so that the underside of the washer (MN189) is level with the machined faces of the bridge platform located at the rear base of the machine (this distance is approximately 10mm). Now place the machine on the top face of the cylinder block as shown. Take the hold down shoe (MN7) assembly and slide it into the base of the machine so that anchor screw slots into the shoe. Now turn the hold down screw (MN92) clockwise until the machine is securely clamped down. It is advisable that the screw head on the anchor clamp should be midway between the front and rear of the machine so as to exert an even pressure across the base.


When either of the above procedures has been completed, the machine is ready to bore the cylinder as follows :-






At this stage, the cutter has not been accurately located over the centre of the cylinder to be bored and this is the next step.


1. Using the chart in the top of the toolbox, select the set of centralising pins required for the cylinder to be bored. Note that the size chosen should correspond to the existing bore size and not the finished or required size. Exchange these pins for the set in the machine and retract them fully by unscrewing the actuator rod (MN13). The smallest set will lie flush with the cutter head (MN78) and larger sizes can be felt to be secured by their locating mechanism.


2. Using the crank handle (MN71) lower the cutter head a little way down the cylinder. (To do this, the sliding clutch collar (MN29) must be pulled towards the operator). It may be necessary to release the machine by slackening the hold down screw (MN92) and moving it more directly over the cylinder to be bored.


3. Slacken the hold down screw (MN92), tighten the actuator rod (MN13) and observe that as the centralising pins move out, the cutter head is drawn precisely to the centre of the cylinder. When the pins have located the machine in a central position, it will be noted that the cutter head cannot be easily revolved by the spindle knob (MN63). If the spindle knob can be easily revolved, then the set of centralising pins selected are too small and should be exchanged for the correct (larger) set.


4. Tighten the hold down screw (MN92), fully retract the centralising pins and raise the cutter head to its uppermost position. Check that the pins are in their locations, the smallest set will be flush, other sizes can be checked by pulling. A located pin will be reluctant to move from its location.


The machine is now clamped central to the cylinder to be bored.






The size of bore to be produced must obviously be decided before proceeding further. The machine is capable of producing a finish, which is so smooth and so accurate that only light polishing of the surface is needed to finish the surface. Notes in section 7 give some guidance to the clearances required by modern pistons.


1. Select the cutter required, using the chart in the top of the toolbox.


2a. Adjust the setting micrometer (MN74) to a size approximately 0.5mm larger than the size required.


2b. After slackening and retightening the setting pin clamp screw, this oversize position of the setting pin can be achieved. In the case of the 3 larger tools, an internal spring simplifies the operation.


2c. Slacken the setting pin clamp screw just sufficient to allow the micrometer thimble to be revolved so as to move the setting pin up to the required setting size.


2d. Back the micrometer thimble of by one quarter of a turn and fully tighten the setting pin clamp screw.


2e. Re check the size.






With the machine clamped central to the cylinder to be bored, we are now ready for the final operation, the rebore.


Before inserting the cutter into the machine, wind the column down through the cylinder to a point where the cutter will finish cutting and set the trip rod switch to switch off the motor at this point. Now wind the column back to its uppermost position.


Fit the tool, which has been set into the cutter head, and secure it by tightening the tool clamping screw, MN146. Check finally that the centralising pins are fully retracted and secure in their location (see Section 3.4). Wind the cutter down to within a few millimetres of the cutting position, the engage the automatic feed by pushing in the sliding clutch collar. A short delay will occur before engagement of this clutch can be effected.


The machine will no bore the cylinder to the correct size and switch off when the operation is completed. When the machine has stopped, disconnect it from the electricity supply and retract the column manually, you will need to withdraw the sliding clutch collar as detailed earlier. To prevent the cutter from marking the bore, the spindle knob (MN63) should be revolved so that its fixing screw is to the front of the machine. Thumb pressure on the column in line with this screw (which is in line with the cutter) will prevent the tool marking the bore.







Select the cutter to be sharpened and place this in the lapping jig (MN121) with the identification marks of the cutter next to the knurled screw. Ensure that face of the diamond lap (MN66) is lubricated by lapping oil soaked into the felt wick.


Experience has shown that with typical Japanese motorcycle cylinders, 20 or 30 cylinders can be bored before re-sharpening of the tool is necessary. Always keep the cutting edge to a maximum width of 0.25mm. The easiest way to achieve this is to first sharpen the front and back faces to as to remove this centre cutting edge, then just touch the cutter on to the diamond lap when it is located on the centre hole on the lapping jig.






Establishing the finished size required :-

In the case of car cylinders, this is usually a nominal size, which is printed on the box in which the pistons are supplied. In the case of motorcycle cylinders, it is more usual to measure the piston (at the bottom, front to back) and add the clearance recommended by the manufacturers, to establish the finished size required. In practice pistons of a particular "nomimal" size may vary considerably, even to the extent of a four cylinder machine requiring bores of sizes which vary by as much as 0.05mm. As a general rule piston clearances for modern Japanese motorcycles will be in the order of 0.03mm with notable exceptions for some models. If the bore is to be run without further finishing or light "deglazing" using "Flexhone" type bore brushes, this is the size to be set on the setting micrometer. In this case is best to bore the cylinder using the fine feed setting. If the bore is to be finished using a honing machine, an allowance of 0.04mm should be left and the bore may be bored at the "normal" feed rate setting.


Never run or leave the machine without the setting pins or cutter in position. This prevents dust from entering the cutter head and causing setting or centralising problems.


When boring diameters of less than 58mm, it is possible for the rack to strike the cylinder if it has been mounted on its base so as to protrude into the throat of the machine. Accordingly it is most important to set the stop as described in section 5. In most other circumstances, the safety stop will in any case stop the machine when the limit of its travel has been reached.


Restrict the maximum cut to 0.75mm in the interest of tool life. This is particularly true in the case of ported cylinders. Cuts of up to 2mm are permissible in aluminium cylinders.


Inconsistency of size and finish is almost always due to poor condition cutters. Keep all 4 tools sharpened alike and the machine will produce consistent results throughout its range.


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