DETROIT DIESEL 53
Fig. 38. - Comparison of Former and New
Design Injector Parts
near-perfect fit between the needle
valve and tip.
Fig. 39. - Tightening Injector Nut by Hand
Before reinstalling used injector parts, lap all of the
the block in a figure eight motion several times to give it
sealing surfaces indicated by the arrows in Fig. 31. It is
a smooth finish. Do not lap excessively. Again wash
also good practice to lightly lap the sealing surfaces of
the part in cleaning solvent and dry it with compressed
new injector parts which may become burred or nicked
7. Place the dry part on the third block. Do not use
Lapping Injector Parts
lapping powder on this block. Keep the part flat and
Lap the sealing surfaces indicated in Fig. 31. and the
move it across the block several times, using the figure
chart as follows:
eight motion. Lapping the dry part in this manner gives
it the "mirror" finish required for perfect sealing.
1. Clean the lapping blocks (J-22090) with compressed
air. Do not use a cloth or any other material for this
8. Wash all of the lapped parts in clean fuel oil and dry
them with compressed air.
2. Spread a good quality 600 grit dry lapping powder
on one of the lapping blocks.
3. Place the part to be lapped flat on the block as
shown in Fig. 33. and, using a figure eight motion,
move it back and forth across the block. Do not press
on the part, but use just enough pressure to keep the
part flat on the block. It is important that the part be
kept flat on the block at all times.
4. After each four or five passes, clean the lapping
powder from the part by drawing it across a clean piece
of tissue placed on a flat surface and inspect the part.
Fig. 40. - Tightening Injector Nut With Torque
Do not lap excessively (refer to the chart on minimum
5. When the part is flat, wash it in cleaning solvent and
dry it with compressed air.
6. Place the dry part on the second block. After
applying lapping powder, move the part lightly across
1972 General Motors Corp.