What dictates too much advance timing?

[RSchwarzli]

A comment was made on another thread that when he advanced the timing to 1. 60mm lift that the motor sounded off and he backed it off so as to not damage anything.



It got me thinking.



What is too much advance and how would one know? I have mine set at 1. 79 mm lift and it sounds OK. Yeah, a bit cracklier but that is to be expected as I also adjusted the pump at the same time! I woudld not say anything sounds bad or runs rough, I actually thought it was pretty good!



Thoughts? Just want to make sure I am not hurting my baby!



Thanks!



Robert

 

[NIsaacs]

Probably not scientific, but I have mine with a slight rattle with engine cold and KSB kicked in. When the engine warms up enough to kick out the KSB, no more rattle.



Nick

 

[PToombs]

Mines at 1. 65 or . 69, I can't remember which. I had it up to 2. 25 and it rattled a little. I backed it back down because the head gasket is leaking pretty good. The truck ran good, I just didn't need it blowing up right then. I'd put it back and not worry about it after I change the gasket and stud it.

If it sounds ok and you're not worried, run it. If it bothers you, back it down.

 

[Mhannink]

i dont know the mm of lift but these same engines in marine app run as much as 25 degrees of timing so i think youd have to advance it a lot in order to damage things

 

[HHhuntitall]

If it's knocking, you're wasting compression, and eventually may cause problems with your wrist pins and pistons. A little knock isn't too bad on acceleration, but if it sounds like Darth Vader lost his helmet in the valve train, that's not good! Your injecting your fuel in the cyliner and beginning the combustion cycle before TDC. Your actually hurting yourself because you're slowing the piston before it reaches TDC. If you're going to get the maximum burn cycle, you need to have the fuel injected as soon as possible, but if you're overdoing it, it starts to hurt you. Laws of diminished gains, gentlemen..... :{

 

[cerberusiam]

i dont know the mm of lift but these same engines in marine app run as much as 25 degrees of timing so i think youd have to advance it a lot in order to damage things

Too much is what your specific engine doesn't like by telling with injection rattle. It different from engine to engine because of the variables. Pump condition, pump settings, injectors, etc, all play into optimal timing settings.



What will cause too much rattle on one engine may not be enough on another. Just have play with it to find the happy place on yours.

 

[RSchwarzli]

Cool. Thanks guys!



If I hear my motor rattle I will get worried... .

 

[mysteryman]

pump timing and cam timing are closely related. The more retarded the cam is the more advance on the pump will be needed to get it to run well. And vise versa.

Cam timing is fixed. the only thing that changes it off of spec are manufacturing tolerance ranges. (+ or - spec factory screw ups) Cummins had some of the worst

quality control on the 5. 9 that I have ever seen!!! This is why some trucks run real good off the show room floor and others are like a stick in the mud .

This is why some trucks need more advance that spec to run well while others need less. I do know that too much advance will cause to high of cylinder pressure resulting in blown head gaskets. I have found that trucks that require more than 1. 5 mm advance to run well usually have other issues. Cam timing being at the top of the list

 

[Mikey-KE7LBB]

Another thing that would affect how much advance you need is the pop pressure of the injectors themselves. As the springs get weak, they will naturally open sooner than new or custom injectors that may be set to pop a couple hundred pounds over stock pressure.