VP44 Offset Key

[ICEMAN86]

So I thought I would pose a question today, since this is something I’ve been dealing with all day. What exactly does the offset key do in regards to timing? I’ve searched the inter webs and I can’t find anything more than a generic, “It works with timing the pump”, or “The key has to be calibrated to each pump”. What does it do? Is there a hidden ignition pickup or sensor in the gear cover that reads the key? Reason I’m asking is because my key is crushed (My F-up). I think at some point between 1998.5-2002, Dodge took either the crank or cam sensor out of the truck when built. I have an 01, and it only has one of those sensors. I’m wondering if the key is irrelevant on those later trucks not equipped with the cam/crank sensor (still can’t remember which one I have). Any clarity on what the hell that key affects regarding timing would be much appreciated. 

[dripley]

You have a cam sensor and not the crank and cam sensor. As far as the key is concerned I believe it is offset slightly to align the pump with the cam gear for timing purposes. If it is not aligned the truck timing is off and the truck runs like crap. The key is numbered and replacements can be bought. The key number is engraved on the pump also, just dont remember where.

[ICEMAN86]

Would a Cummins dealer have a replacement? I need an 028 key. I was about to use a regular key, but didn’t want to go through the trouble if I need an exact size key. 

[dripley]

You definitely need the exact key. Cummins may have them I dont know. You could call Diesel Auto Power or anyone who sells the rebuilt pumps to source one I would think.

[ICEMAN86]

If the point of the offset key was to align the pump with the cam gear, then why is the pump position fixed? Because the cam gear position is dependent on the pump shaft, and it has to mesh with the other gears. It seems to me that the key is like any other woodruff key and cannot affect timing unless it is acting like a reluctor and pinging a sensor. I think tomorrow I’ll put the pump in with an AUTOZONE key and see if it works. Found one that fits snug, so I’m not worried about it falling out during install. 

[dripley]

My apolagies, I should have been clearer.  It aligns the pump shaft and not the pump. The pump gear and the pump are fixed. The only sesor there reads off of the cam gear. If it was me, I would get the right key just because I would not want to take it apart again to replace it. But who knows maybe you'll get lucky.

[ICEMAN86]

At this point I’m getting pretty good at removing the pump! I just need the truck since I am moving this week. I’m going to call Cummins first thing when they open Monday, if they don’t have one, I’ll order online and see if the generic key works in the mean time. 

[Mopar1973Man]

Here is the whole key list...

 

 

[ICEMAN86]

Thanks 

[wil440]

It is all quite easy to figure why the timing key.... tolerances simple as that, timing has to be bang on to the degree the tolerances on crank, crank gear, cam and cam gear won't be anywhere close so off set key gets it to where it needs to be from the factory brand new, it could also change in theory when VP44, crank, cam or gears are changed but I'd guess VP44 is the one, one thing to remember bigger cummins use timing to increase power but this is done by moving cam followers in relation to the cam centreline and fuel timing changes

[ICEMAN86]

Since the shaft on the pump is tapered, is the offset changing the engagement depth of the pump gear to the cam gear? I don’t see that affecting timing as long as the gears mesh. 

[Mopar1973Man]

There are keys up to 2.5-degree offset...

https://powerdrivendiesel.com/product/2-5-degree-offset-key/

Edited April 28, 2019 by Mopar1973Man

[dripley]

The key allows the shaft to rotate to a different position in the pump gear as the key picture @Mopar1973Man posted demonstrates. The tapered shaft does nothing for timing.

[ICEMAN86]

Ahh, lightbulb! Now it makes sense, the pic definitely helped. The key changes the degree of the pump shaft inside the gear similar advancing a distributor on a gasser. Thanks for the patience describing  how it works. The whole time I was thinking the offset was vertical, which was why I had a hard time making sense of it. Thanks for the help guys.