Usage:
All Engines
- SUPPLEMENT: 01/20/86
SERVICE MAGAZINE, OCTOBER 28, 1985, PAGE 5, "COMPARISON OF FUEL TIMING TOLERANCES FOR FIELD SETTINGS". Add a note to this article that it does not apply to 3500 or 3600 Series Engines because they have unit fuel injectors. None of the three timing methods discussed in the article is used on these engines.
Also, in the third line of the section, "Tolerances For All 3406B Engines", replace the word "tolerance" with "advance".
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Reference: "Engine Information Plate Contains More Data; Use Of Performance Specifications" in this same issue.
This topic applies to any engine with any type of Caterpillar fuel system. Fuel timing can be done by pin timing on the engine, fuel flow timing, or engine dynamic timing. Each of the three methods will result in a slightly different timing setting. This can be confusing to dealers and users, particularly if the fuel system parts are excessively worn. For example, you can expect a 2° difference between the static fuel flow setting method and engine dynamic timing with excessively worn parts.
Engines such as D353, D379, D398 and D399 Engines, that have had lifter settings adjusted on the engine, can be timed very accurately with the pin method. However, if the lifters are worn, the fuel flow method is more accurate. But, since worn lifters usually mean wear in the plunger scroll area, engine dynamic timing is really the best of the three methods. This method accounts for wear in all the fuel system parts. This may be the reason for possibly a 2° variation between the static fuel flow setting method and engine dynamic timing method.
In order to allow for the expected tolerances on fuel system parts with little or no wear, the following timing tolerances are to be used in place of previous tolerances in the field:
... Pin timing. This is changed from ± 1° to ± 2°, which is usually equal to one-half of the diameter of the timing bolt hole depending on engine model. Note this change in the Service Manual Specifications. Pin timing is recommended only to install the injection pump housing on the engine, although in some cases, it can provide acceptable complete engine timing.
... Static fuel flow method. This tolerance remains ± 1°. Change the Testing and Adjustment Module where stated otherwise in the Service Manuals.
... Dynamic (engine running) fuel timing method using the 6V3100 Timing Indicator Group. This tolerance is now ± 1.5°. This is due to the various tolerances from flywheels, flywheel housings, etc. which the indicator uses as part of its measurement. Refer to Special Instruction SEHS7742-03 and note this change on Page 21 under the topic "Timing Tolerances". Add this also to the Testing and Adjusting Module for the Service Manual on 3406B Engines.
... For all engines except those with a full load rpm of 1200 or less, do not measure dynamic timing below 1000 rpm. Unstable readings are often obtained below 1000 rpm. Presently, the OT Microfiche on fuel settings shows fuel timing for low idle. This will be changed when practical to about 1000 rpm and will probably be referred to as "base rpm", not "low idle".
Tolerances For All 3406B Engines
Dynamic timing is recommended for 3406B Engines in all applications. The new scroll fuel system on these engines has resulted in a dynamic "port effect tolerance" of about .2° per 100 rpm instead of .1° per 100 rpm as presently published in service publications. This is most noticeable on 3406B Truck Engines 7FB1-Up. This has caused many of these engines to appear out of time, when actually they were not out of time under dynamic (running) conditions. This variation will be changed in the OT microfiche.
Also, refer to Special Instruction, SEHS7742-03. On pages 16, 17, 18, and 19, add a statement that "3406B Engines have .2° advance per 100 rpm". Refer to the sample graph (SEHS8140) on Page 34 and write the same statement by the words "Port Effect" at the bottom of the graph.