Measuring, Honing and Silicon-Lapping Cylinder Bores
For Special/Conventional Tools, Tools and Equipment
NOTE: The light metal cylinder bores are very sensitive to damage, scratches and dirt and therefore should be treated very carefully.
When honing, the cylinder bores should be matched to the dimensions of the existing repair stage pistons with group numbers 0, 1 or 2. while maintaining the specified piston clearance.
Measuring
Inside measuring instrument with setting micrometer:
When measuring the cylinder bores, use a measuring instrument with spring-loaded measuring tip to prevent score marks on cylinder running surface through the measuring point contact and premature wear of the instrument measuring pins.
Set the self-centering inside measuring instrument to the cylinder diameter before measuring, and measure at 22 - 24 °C room temperature.
The aluminum surface recession (0.5 - 1.5 um) between the silicon crystals can only be measured indirectly via the mean roughness (Rz) after silicon-lapping (end condition).
The specified exposed depth of the silicon crystals is obtained by the temporally limited control during silicon-lapping and the choice of silicon paste used.
Honing and silicon-lapping
With severely scored and worn cylinder (> 0.10 mm) etc. the cylinder bores can be honed to the specified repair stages.
After honing, the silicon crystals must remain intact and flattened on the cylinder surface.
The honing processes (prehoning, finish honing and polishing) must be followed by ..silicon-lapping" according to the Sunnen process in order to expose the silicon crystals.
Omission of the job ,,silicon-lapping" invariably leads to piston seizures.
CAUTION! The following jobs must only be carried out with a honing machine with honing oil filter and oil cooler.
The silicon particles must be separated from the honing oil by filtering.
The honing oil must be cooled to a constant temperature of 20 °C to avoid excessive heating of the cylinder crankcase.
In order to obtain a good honing quality it is necessary to use only the specified honing oil.
1 Set up honing machine CK-10-G.
Carry out all honing and lapping work without directional guide shoes.
The protrusion of the honing stone (arrow) is 14 mm.
2 Cut the lower protrusion of the bronze strip on the main guide shoe (arrow) as the recess at the bottom of the cylinders allows only approx. 14 mm protrusion of the honing stone.
Dimension a = 70 mm
3 The specified stone sets of 89 mm length must be shortened to 70 mm. To do so, cut the honing stone at the top (not the holder) using a metal saw.
4 Torque the crankshaft bearing cap bolts and nuts in the sequence of the tightening diagram with 50 Nm.
5 Fix disassembled and cleaned cylinder crankcase with fitted and tightened crankshaft bearing caps in the honing machine by means of the square steel.
6 Adjust stroke (cylinder length) on the stroke scale according to the table "Prehoning" (below).
7 Adjust stone projection (arrow) with the gauge according to the table below.
8 Adjust feed (arrow) according to the table below.
9 Adjust strokes per minute and revolutions per minute according to the table.
Prehoning - Setting up of honing machine:
10 Prehone all cylinder bores with full honing oil supply up to approx. 0.08 mm before the final dimension, since otherwise the silicon crystals will be torn out or damaged by the cutting pressure.
CAUTION: When measuring directly after prehoning, a dimension of approx. +0.02 mm is obtained due to a rise in temperature.
The heating-up of the cylinder crankcase is also dependent on the ambient temperature.
11 Insert stone set for fine honing and cut to size as described below.
12 Set up honing machine according to the table "Fine honing".
Fine honing - Setting up of honing machine:
13 Fine-hone all cylinder bores with full honing oil supply up to approx. 0.02 mm before reaching the final dimension.
CAUTION: Measuring directly after fine-honing, a dimension of approx. +0.01 mm is obtained as a result of temperature increase. The heating-up of the cylinder crankcase is also dependent on the ambient temperature.
14 Chamfer cylinder bores according to above image prior to polishing.
15 For chamfering, use a suitable hand milling tool with an angle according to the above image.
16 Insert stone set for polishing.
Prior to machining, the new polishing stones should be straightened in the narrowest cylinder bore.
17 Set up honing machine according to the table"Polishing".
Polishing - Setting up of honing machine:
18 Polish all cylinder bores with full honing oil supply until the end dimension has been reached.
19 Allow cylinder crankcase to cool down.
20 Measure cylinder bores, while taking into account the required cylinder diameter (group No.) for the existing pistons and the specified piston clearance.
Repolish if required.
21 Clean cylinder walls with filtered honing oil to remove all silicon particles and to avoid scratches during the subsequent silicon-lapping process.
22 Press felt inserts (C 30-F 85) into the holders CK-3130 and these into the stone holders CK-3035.
CAUTION: After the felt inserts have been pressed into the holder, remove all material which has been scraped off in the process.
23 Set up the cylinder diameter by means of the setting gauge.
24 Soak felt inserts with filtered honing oil and insert into the honing head.
25 Cut honing oil supply.
26 Set up honing machine according to the table "Silicon-lapping".
Silicon-lapping - Setting up of honing machine:
27 Thoroughly stir silicon paste AN-30 and fully coat the dry cylinder walls.
28 Likewise coat the felt inserts with silicon paste.
29 Introduce honing head with felt inserts into cylinder bore.
30 With honing machine running, slowly turn feed wheel to the right until the indicator reaches 30 %.
31 Set feed scale to 18 divisions.
The honing machine will switch off after approx. 80 seconds. The cylinder surface will then have a dull appearance.
No honing marks will be visible.
The roughness is 0.001 - 0.003 mm.
32 Thoroughly clean cylinder bores of all silicon traces using filtered honing oil and a suitable brush, then dry.
Used silicon paste may not be reused.