Engine/Transmission (1994 - 1998) Complete Camshaft Confusion

[HHhuntitall]

Last year, I purchased two engines removed from '96 Ford F-650s purchased by the City of Los Angeles. As I understand it, the trucks were driven to the nearest dealer and the diesel engine removed and replaced with a natural gas motor. The medium duty engines I bought had 73 and 103 miles on them. I put the latter in my '97 3500 and since have had a few problems. These engines were in front of Allison automatics, and the cams are timed at 11degrees, if I'm not mistaken. Now, that's fine and dandy, except I put a 6speed in my '97, and I am off road very frequently, usually at lower RPMs in lower gears, often with a trailer. The problem I'm having is excessive fuel usage and slow response, and the smoke to follow. I've adjusted the pump in every direction, even too far, with a blown head gasket to prove it(should've ordered a cam from Piers or Sheid then!!). I've thought about a new cam, but I don't want to pull the head again for the lifters. That's when I thought about jumping a gear on the cam. That's 2. 5 degrees one way(360 degrees/72 teeth/2 camshaft speed to crank), which would put the cam at 13. 5, right? What's that gonna do to pump timing, too? I've never fooled with camshaft timing on a Cummins, but I know on a Gas engine, you have to adjust timing to increase torque. And on a Chrysler RB-block, i usually like to have my cams around 14-16 degrees. Anyway, who can help me here? I'm planning on wood-doweling the lifters up, pulling out the cam just far enough to turn it one tooth. I guess that's gonna leave the pump timing alone, as BDC on the valves is going to stay at the same place, right? I've got the pump "adjusted" past where it should be, which doesn't help the smoke, but I need it to pull like the old motor. It's great over about 1600 RPM, building boost and not smoking like it should, but I'm guessing that's because it was for an automatic. One of you 12 valve racers has got to have tried this before. Help me out, please!

 

[Joseph Donnelly]

You seem to be confusing cam timing and injection pump timing. You want injection pump timing to be around 13. 5 to 15. 5 degrees. Cam timing is a different thing, and cannot be described so simply. You have “straight up”, advanced and retarded positions. You need to get a degree wheel and see where the valve opening and closing events are relative to top dead center before messing with cam timing. Your stated preference of 14-16 degrees on a camshaft is not correct. I believe you are actually referring to pump timing. It is very unlikely that the cam timing should be changed. The pump gear runs off the cam gear, so if you try changing the cam one tooth you will change the pump with it if you move the pump gear. If you leave the pump gear unmoved, its timing won’t change. One tooth on the 72 tooth cam gear is 5 cam degrees or ten crank degrees, too big a change to try in one shot unless you know where the cam timing is and exactly where you want it to go.



You need to back out the lift pump because it has a pushrod on a cam lobe, if you move the cam as you described. If you move the camshaft one tooth, the amount of valve opening at BDC (and anywhere else they are open) will be changed.

 

[HHhuntitall]

Joe,

Ok, thanks for the info. I was afraid of doing it not knowing more about it than I do. That's what I came here for. I have a crank degree wheel I use on Gas engines with a wire and tape, I suppose it should work the same on the Cummins using the valves as indicators. I'll just have to pull it down. I need to live further up North so I have a little more time in the shop. If this gets too complicated I may just pull the head and get a new cam and lifters. Any recommendations on a RV/towing camshaft? I've done some business with Scheid Diesel, but I'm not sure what all they have available. I've got stock heads other than the orings, and a stock turbo. I'd like to put an hx40 on it, I just haven't the time to fix the downpipe yet. I'll probably stop there on this truck, as it's got to have a limit as a work truck. Thanks again for your time and help.