NUT 1565970 - Caterpillar

3500 Family Of Engines;
D11N, 776B Tractors;
777B, 785, 789 TrucksReference: Service Magazine; June 1, 1987; Page 17; "Fuel Injector Trim Bolt," on all 3500 and 3600 Families of Engines. Service Magazine; November 21, 1988; Page 8; "One Piece Tappet Used In 11 mm Fuel Injectors," in the 3500 Family Of Engines. Service Magazine; August 28, 1989; "New Fuel Injectors Available For Parts Service," in the 3500 Family Of Engines. This article replaces the January 19, 1987 Service Magazine article "Fuel Injector Reference For 3500 Family Of Engines."
The 3500 Family of Engines has a number of different fuel injector assemblies for different operating speeds, power ratings, and product improvements. This has caused some confusion. This article will summarize: ...all of the injectors that have been used....the differences between the injectors....how to identify different injectors....which injectors are used for various applications, operating rpm, and power ratings.
All injectors for 3500 Family of Engines are one of two types. For purposes of this article we will refer to then as Type 1 and Type 2. Type 1 injectors have 10.7 mm (.42") diameter plungers. Type 2 injectors have 11.0 mm (.43") diameter plungers.
There are other basic design differences between the two types. Refer to Illustration 1 and 2 for examples of Type 1 injectors, and Illustration 3 for an example of a Type 2 injector. When not installed, injectors may be identified by the injector case. Type 1 injectors use a one piece case that encloses the plunger and barrel assembly as well as the nozzle assembly. Type 2 injectors use a case that encloses only the plunger and barrel assembly and a separate cone that encloses the nozzle capsule. When installed in the cylinder head, Type 2 injectors can be identified by the trim bolt as shown in Illustration 4. This trim bolt must not be adjusted (see Service Magazine; June 1, 1987; Page 17; "Fuel Injector Trim Bolt"). Newer Type 2 injectors may also be identified by the part number etched on the tappet. Type 1 injectors have no trim bolt. Older Type 2 injectors may also be identified by a two piece tappet as shown in Illustration 5 (see Service Magazine; November 21, 1988; Page 8; "One Piece Tappet Used In 11 mm Fuel Injectors").
Illustration 1. Type 1 injector.
Illustration 2. Type 1 injector tip has identification information which shows orifice diameter in mm, number of orifices, and spray angle.
Illustration 3. Type 2 injector.
Illustration 4. Location of trim bolt on Type 2 injectors.
Illustration 5. Two piece tappet.The plunger scroll type give the injector its most unique characteristics. The characteristics follow: ... SINGLE SCROLL INJECTORS do not have variable injection timing (time when injection starts). The beginning of injection is fixed as the plunger rotates from the low to full fuel position.... DOUBLE SCROLL INJECTORS have variable injection timing. The beginning of injection advances as the plunger rotates from the low to full fuel position.... TIMING RETARD INJECTORS have variable injection timing at lower engine loads and constant injection timing at higher