TRANSMISSION AR 4178818 - Caterpillar

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.