timing rattle?

[olboyowl]

was messing around on the interstate last night with another guy. was slowed down to about 85ish and went to get back on it and had a slight rattle for a second. im running max 27* of timing and have never heard any rattle in any of my 20+ logged runs from 0-100 or 60-110. my thoughts are it was pilot kicking off (kicks off at 2600 rpm). can timing rattle come and go like that and if so, should i drop timing back a few *'s? thanks for any info

denny

[2007 5.9]

If you have rattle...drop 2* and recheck.

Are you commanding alot of fuel when it knocks?? Sometimes too much fuel can knock and sound like timing. One way to see is when it makes it noise, is your exhaust clean or are you blacking out the road??

[DoghouseDiesel]

Denny,

Check your TOTAL timing also (i.e. Pilot AND Main).

If you adjust main without regard to pilot, you can get some SERIOUSLY ugly timing values.

I've got 4 charts sitting in front of me right now that I'm analyzing right now on this same thing....I've got one tune that is has TOTAL timing in excess of 90* BTDC in some spots.....that's BAD juju.

[tinman]

When you say total timing, you mean when the pilot starts in relation to TDC, correct? If you advance the main timing, should the pilot advance the same amount or a percentage?

[2007 5.9]

Yes..pilot is referenced from main

[olboyowl]

thanks for the replies fellas. les, i wish i had looked down at the rpms so i would have some reference with were the fuel was. im gonna go out on a limb and say it was between 130-150mpa. it was kinda on the humid side up here last night so i was a little more hazier then usual. it runs 95% smoke free during the day time. rich, i'll fire up the laptop here in a few and add up the values. i did lower pilot timing on the file. there is no were in the whole table that is over 10*. i'll get some more info up if a bit. thanks for the help

denny

[DoghouseDiesel]

Tinman, yes, like Les said, if you advance the main timing and don't change the pilot, that pilot is referenced off of the main not TDC so it gets bumped up along with it. This can make for some REALLY aggressive timing.

[olboyowl]

looks like 47.7* with main and pilot values added together is the max timing # im coming up with. just for reference, the higher timing #'s are between 1200-2200rpm and from 75mm3-140mm3. gonna drop some more pilot timing (gonna start with 3-4* in the area listed above). is there a minimun amount for pilot timing? again, thanks for the info. much appreciated

denny

[olboyowl]

dropped the pilot timing so that the highest * is 4.8 and in conjunction with main timing, the highest * is 42.8 at 2200rpm at 140mm3. truck ran fine on the way home from work his morning. gonna take it for a spin and log it this afternoon.

[killerbee]

High fuel pressure/timing combo can also create the signature rattle. Or as you hinted, loss of pilot briefly.

[olboyowl]

i could not get the truck to replicate the sound this afternoon. with pilot timing decreased and a max 42.8* total between main and pilot, the truck ran all but identical to the way it did before. theres still a little left in it. very small haze at wot, 47*, 3100us, identical 160mpa a/d in the log, 35-36psi, and at 110 and 3,xxx rpm, egts were at 1550. very happy with how it runs.

[TexasCummins]

Does anyone know if the pilot timing degrees have the 20* bias or is it truly what it says due to it referencing the main?

[2007 5.9]

Pilot is correct as it sits...it is completely referenced from main timing. No need for 20* bias...

[TexasCummins]

Thanks Les!