3406B injection pump differnces

[brahamfireman]

I am trying to find info on how to tell the difference in a 350/400 HP pump and a 425hp pump. everyone tells me the 425 pumps are different so, how do I tell the difference. casting numbers or are cams inside the pump different?? how will I know unless I take the pump apart??

thanks guys

Diesel Rod

[ericjack]

The 3406B injection pump is basically the same from 310HP all the way up to 425HP. The difference is the static timing on the cam. It is engraved on the end where the timing advance goes. Timing has lowered through the years for emissions reasons. The early 3406's had 26 to 28 degree timing. Along about 1987-88 timing dropped to 18 to 24 degrees, and finally the last 3406B's had 14-16 degrees. Look for the serial number on the block of the engine. It should be either 7FB or 4MG prefix. Most 7FB's had 24-28 degrees while most 4MG's had 16-22 degree timing. As far as the governor and barrels and plungers, they are the same on all applications.

Around 1991 Cat changed the injection pumps and went to bigger cam bearings and plungers. This can be noticed by 7E-5888 cast in the housing, while 3406B pumps had 7W-3906 cast in the pump. Timing also dropped to 9.5-11 degrees on the later pumps. Please call me if you have any questions, I will be glad to help.

Also, a good rule to remember: Later pumps will push older nozzles. Older pumps will not push newer nozzles, (not long anyway).

[brahamfireman]

thanks very much eric. i got your Pm also and I am sure I will be calling ya sometime with more questions.

engine was a 1986 B model factory 350HP, upgraded to 400 in 2002, also had the Air to air added at the time.

I just looked and its a 7FB engine. also I am told this engien has variable timing on it. there is a large cone on the front cover over the pump gear, how much is this going to affect pump mods??

[ericjack]

All 3406 engines have variable timing advances. The early (7FB) advances were more prone to problems than the later (4MG) engines. A wore or faulty timing advance will greatly affect performance. You need to look and see what type of advance it has to indeed prove it is a 7FB series. All 7FB and early 4MG engines had 4 bolts holding the advance on that were 12 point. Later advances had 6 point bolts. Pull the bolts and advance out and hold the snout with the o-rings and try to spin the outer housing. If you can spin the snout, the advance is wore and NOT operating properly, meaning the timing is not advancing to keep up with enging speed. Another rough check is to crank the engine and get it up to operating temperature. While idiling, rev engine up to high RPM. If the engine stutters, or puffs white or grey (not black) smoke, the timing is not advancing right. This will result in low power, excessive smoke, high EGT, and poor fuel mileage. By the way, adding air-to-air to the engine was one of the best mods you can do. Let me explain how important air-to-air is. The ONLY difference between a 350 and a 425 is in fact air-to-air aftercooling. The nozzles were even the same on most applications. The real important key is the fuel settings on the pump were actually lower on the 425 than the 350, thus proving the power advantages of ATAAC.

Let me know if I can help. I hardly ever have time to check messages on here, so email is the best way to get me. It is eolt@wildblue.net Thanks Eric