DETROIT DIESEL 53
Fuel Injector 2.1.1
accidentally placed on the lapped surfaces located higher up in the spray tip. The slightest
lapping action on these surfaces can alter the near-perfect fit between the needle valve and
Before reinstalling used injector parts, lap all of the sealing surfaces indicated by the arrows in Fig. 31. It is also good
practice to lightly lap the sealing surfaces of new injector parts which may become burred or nicked during handling.
Lapping Injector Parts
Lap the sealing surfaces indicated in Fig. 31 and the chart as follows:
Clean the lapping blocks (J 22090) with compressed air. Do not use a cloth or any other material for this purpose.
Spread a good quality 600 grit dry lapping powder on one of the lapping blocks.
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.
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. Do not lap excessively (refer to the chart on minimum thickness).
When the part is flat, wash it in cleaning solvent and dry it with compressed air.
Place the dry part on the second block. After applying lapping powder, move the part lightly across the block in a
figure eight motion several times to give it a smooth finish. Do not lap excessively. Again wash the part in cleaning
solvent and dry it with compressed air.
Place the dry part on the third block. Do not use lapping powder on this block. Keep the part flat and move it
across the block several times, using the figure eight motion. Lapping the dry part in this manner gives it the "mirror"
finish required for perfect sealing.
Wash all of the lapped parts in clean fuel oil and dry them with compressed air.
Use an extremely clean bench to work on and to place the parts when assembling an injector. Also be sure all of the
injector parts, both new and used, are clean.
Study Figs. 34 through 37 for the proper relative position of the injector parts, then proceed as follows:
ASSEMBILE INJECTOR FILTERS
Always use new filters and gaskets when reassembling an injector.
I. Insert a new filter. dimple end down, slotted end up.
Fig. 40. Tightening Injector Nut
Fig. 39. Tightening Injector Nut
March, 1973 SEC. 2.1.