oaky so the wierdest thing happened on my way home the other day, i was driving along at about 35mph and i stomped on the go pedal to pass my buddy and then all the sudden right before my truck really started pulling away it started popping and buckn and missing hard. So i pulled the valve covers the next day and found that one rocker arm, the 4th piston back on the intake valve had about an 1/8th inch or more of gap between the rocker arm and valve spring and i found three other valves that were off too, just not as bad... the thing is, is i just adjusted my valves about 1k ago, and the problem just happened all the sudden... not like the rocker arm was slowly getting loose or something.... plus all the rocker arm adjustment nuts were tight, and i checked every push rod and they are all straight... so i readjusted all my valves and the truck runs fine......???? how could that one valve get that far off? thanks

jason

 

There's only two possibilities I can think of off the top of my head.

Error on the mechanics part or worn cam lobe.

 

I'll tell you what happened, I did exactly the same thing twice. I finally got a clue after doing it twice what I was doing wrong. If you set your valves by turning the engine over and going through the firing order that is what is getting you. I set a mack the other day and the same thing happened( they are similar to our cummins). As I went along I noticed there were valves that were loose. I can't remember the exact details of why it didnt work but, If you set the valves the way I am fixin to explain it, you won't have that problem anymore. If you go cylinder by cylinder, lets say you start with#1. When the intake valve has gone down and is coming back up, you set the exhaust and when the exhaust is starting to go down, you set the intake. This will keep you from setting a valve that is going up a ramp. There is another method that is full proof but I always have to look it up and I don't have the book handy. Anyway, I hope this helps.

 

hahaha well i hope it wasnt something i did as for a warn cam lobe.... would that happen instantly? cause that is what confuses me the most, my truck went from running totally fine to suddenly an 1/8" of play on one valve!? and ive done the valves on my truck probably 10 times or more plus on all my buddys trucks, i just go by the manuals instructions..... never done it cylinder by cylinder....

jason

 

It's possible that the loose valve had little to do with the popping and loss of power. You could be running out of fuel at higher rpm. What kind of lift pump setup are you using? Have you blasted down the road to see if the popping and cutout problem is fixed?

Your timing could have slipped all the sudden, but then again, it would still have the popping and cutout problem even with correctly adjusted valves.

Has the head ever been off or the valve seats worked on? It's possible you have pressed in valve seats and you could have a half dropped seat causing the valve to seat at a lower overall elevation thus showing excess slack or play at the rocker arm.


Just a few ideas, good luck with the trouble shooting!!!

 

Well the truck runs the same as it did before now. The popping and bucking were from my valve being off so much and not opening at teh right times, the truck ran like crap till i got it home and readjusted all the valves, timing hasnt slipped and the truck will still pull to 4k rpms like before. The valve seat idea you got may be what has happened. The head has been off about 3-4 times and everytime i installed new hg and reseat the valves and clean everything up real good. The valve seats are teh same from 1995 so i dont know if they are pressed or what. Thanks

jason

 

12v have integral valve seats, not pressed in.

 

hmmmm thanks.... so im still stumped on this one then... the instant valve and rocker arm gapping like that has me stumped!

jason