Machining Cylinder Bores In Upper Crankcase Section
MACHINING CYLINDER BORES IN UPPER CRANKCASE SECTION
The upper crankcase section is an aluminum alloy product and contains minute particles of pure silicium.
In order to have an usable cylinder surface finish, the cylinder bores have to be machined in a manner that the silicium particles protrude out of the aluminum and therefore pistons and piston rings only have contact with the silicium.
If it is necessary to machine cylinder bores, they can be restored with a SUNNEN CK - 10 / CV - 616 cylinder repairing machine for installation of oversize pistons.
Standard size 100.00 mm
Oversize 1 100.50 mm
Oversize 2 101.00 mm
Single cylinder bores can be machined as required, since pertinent oversize pistons weigh the same as standard pistons.
Prior to machining cylinder bores it is recommended to check the stocks on hand for pertinent tolerance groups and, if necessary, to hone the bore for a certain piston size which is available. There could be problems in supplying pistons of certain tolerance groups depending on circumstances.
The following procedures are necessary.
- Rough turning to 0.1 mm before finished size.
- Dressing to 0.02 mm before finished size.
- Polishing to finished size.
- Lapping with Sunnen silicium mixture.
PROCEDURES
It is absolutely necessary to bolt the upper and lower crankcase sections together with help of the bearing studs prior to machining.
Procedures Torque Threads
3 steps: step 1 20 Nm M 12x 1.5
step 2 40 Nm
step 3 75 Nm
2 steps: step 1 20 Nm M 10
step 2 50 Nm
10 Nm M 6
20 Nm M 8
TOOLS
Machine CK-10 with filter
CV-16 with filter
Grinding attachment CK-3000 or CK-2600
Grinding oil MB-30 or MAN-845
Felt inserts C30-F 85 1 set
Silicium mixture AN-30
Storage box for felt inserts AN-35
Stone holder set for felt inserts CK-3035 A 1 set
instead of honing stones
Stone holder set for honing stones CK-3035 A 3 set
for 3 different stones (types)
Felt holder seat instead of guide CK-3130 A 1 set
shoe
Roughing stone set C30-J 55 ++ shorten to 70 mm length
Dressing stone set C30-J 84 ++ shorten to 70 mm length
Polishing stone set C30-C 03 - 81
Honing Procedures
Perform all honing and lapping jobs without the upper dressing guide shoe.
The protrusion of the bronze bar on main guide shoe no.3 has to be eliminated; flush with guide shoe base.
Setting Up Machine
Roughing adjustment table described in column 1.
Dressing adjustment table described in column 2.
Polishing adjustment table described in column 3.
Lapping - uncovering the silicium crystals.
1. Set up machine as described in column 4 of test sheet.
2. Thoroughly remove all abrasive residue from previous honing jobs with filtered honing oil.
3. Wipe cylinder bores dry and apply a thin coat of thoroughly mixed silicium mixture.
Note: If the silicium mixture is too consistent, it can be diluted by adding fresh honing oil and mixing thoroughly.
4. Holders with felt inserts are now placed in the grinding attachment instead of guide shoe and honing stones.
Adjusting to the cylinder diameter is made with a gage as for the guide rails and honing stones.
5. Soak felt inserts in filtered honing oil and coat with silicium mixture.
6. Stop grinding oil feed; cylinders are lapped without grinding oil!
Machining Cylinders
Guide grinding attachment into bore. Turn feed wheel anticlockwise until felt inserts rest on walls. Start machine and keep turning handwheel anticlockwise until needle of load instrument reaches approx. 20 to 30 %.
Now set scale of feed wheel to 20.
The machine stops on its own after about 80 seconds. The cylinder surface will now be dull and without gloss.
First coat felt inserts with new silicium mixture before going on to the next cylinder.
NOTE: If holder with felt inserts are not being used, they must be kept in the storage box to avoid contact with dirt.
Never reuse old silicium mixture.
A chamfer of 0.5 mm x 30° has to be machined on the upper cylinder wall of machined cylinder bores after finishing the honing procedures.
Clean upper and lower crankcase sections thoroughly to remove abrasion residue and silicium paste prior to assembling.