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Discussion Starter #1
I bumped the timing on my truck this weekend. I had the front cover off to check and re-torque the case bolts, so I was able to remove the pump gear and clean it thoroughly along with the shaft. I used electrical contact cleaner as recommended to me by a quite a few people over brake cleaner. Everything was residue free and torqued to 144ft/lbs.


When does timing usually slip if its going to or is there no rhyme or reason to it? Is there any point when you should be in the clear?
 

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It can go when it wants to. That being said, I’ve put 20k on mine since the last timing adjustment with no issues. I also enjoy romping in the pedal. I would think hard accelerations would be more likely to make it slip.


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Discussion Starter #3
It can go when it wants to. That being said, I’ve put 20k on mine since the last timing adjustment with no issues. I also enjoy romping in the pedal. I would think hard accelerations would be more likely to make it slip.
That's kind of what I figured. I'm pretty confident I got it clean enough and I know it's torqued correctly. I guess we'll see how she goes.
 

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The Uppity 12v Admin
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I had 30-40k on my last adjustment with no issues and no overtorquing of the pump nut.

The injection pump takes a certain amount of torque to drive, and this torque value scales more or less linearly with rack position. An interesting characteristic of the torque is that it's not constant torque. Over time, you can average it to constant torque, but in real life the torque load is best described as a square(ish) wave on a fixed frequency but with variable high-side pulse width or duty cycle. I don't exactly know what injection duration there is at idle, but on a maxed 12mm pump, injection duration at full rack is 32-35 (depending on pump model) degrees of crank rotation. Keep in mind there would have to be 120 degrees of crank rotation for the injection events to bump up against each other (making it truly constant torque), so this 32-35 crank degrees of injection duration works out to a 26-29% duty cycle at full rack.

If the shaft/gear interface is perfect (no oil, no burrs pulled up on either surface from a previous timing slip, proper assembly torque), the largest single contributor to timing slippage is having the AFC tuned in such a way that it allows rack travel to abruptly increase all at once as opposed to a smooth transition. The average pump torque draw spiking is the most likely thing to cause a slippage if one is going to occur.

That said, the properly-prepared and assembled tapered fit connection is strong enough to handle even the nastiest competition-only pumps. Based on what I've seen, the key in an adjustable hub is mostly a gimmick. I ran the numbers last year and came to the conclusion that the key all by itself can't handle the torque of a maxed 12mm pump running at full rack, but it does provide some small amount of safety margin if the hub starts to migrate on the shaft. I believe most of the reason a keyed adjustable hub "fixes" timing slip issues for people is that their stock gear slipped from an assembly issue, which pulled a burr up inside the gear bore which permanently reduced the torque capacity of the connection. The new hub simply has a fresh surface as well as being unhardened (unlike the factory gears), so they conform perfectly to the pump shaft during installation. Then, because the gear itself is adjustable, there's no need to disturb the hub/shaft connection and potentially compromise it.
 

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The 10th Man
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I believe it's most likely to slip upon a sudden RPM change, whether that be a free rev, clutch dump, locked shift, ect
 
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