1989/10/01 Caterpillar

Fuel Injector Reference For 3500 Family of Engines

Usage:

3500 Family Of Engines

Reference: Engine News, June 1987, Page 4, "Fuel Injector Trim Bolt," on all 3500 and 3600 Families of Engines. Engine News, December 1988, Page 1, "One Piece Tappet Used In 11 mm Fuel Injectors," in the 3500 Family Of Engines. Engine News, September 1989, "New Fuel Injectors Available For Parts Service," in the 3500 Family Of Engines.

This article replaces the January 1987 Engine News 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.

Illustration 1. Type 1 injector.

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 Engine News, June 1987, Page 4, "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 Engine News, December 1988, Page 1, "One Piece Tappet Used In 11 mm Fuel Injectors").

Illustration 2. Type 1 injector 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 engine loads. The beginning of injection advances as the plunger rotates from the low to mid fuel position, but does not change from mid to full fuel position. In essence, the timing retard injector acts a double scroll at lower fuel position and then as a single scroll injector at higher fuel positions.

NOTE: Injectors which have either different tip orifice diameters or a different plunger design will have different fuel delivery characteristics. Injectors that vary in these characteristics can not be used as a mixed set in an engine.

The charts show differences between part numbers and engine serial number ranges for the injectors. The color code referred to in the chart corresponds to the color of a small amount of paint applied to the top of the follower.

Chart A contains Type 1 injector information (Type 2 injectors that are direct field replacements are also shown). Chart B contains Type 2 injector information. The Engine Fuel Specifications Microfiche can also be used to identify the type of injector assembly used.