Cummins 6CTA8.3 Injection Timing

[74M35A2]

16 degrees is what the majority of all the 8.3L RV guys run that seek mileage and power gains. They were the largest group of personally owned 8.3's I could find, that tinker with them. Our stock timing is 8 degrees, theirs is 12'ish, and they were noting gains of 2-3mpg by moving to 16, and said any performance mods too much better hold like that. 16 was regarded as the max safe do-not-exceed number for stock head bolts/gasket with no issues. Decreases smoke, decreases EGT. Not really a power gain by itself, but once you add more pump fuel, the results will be further ahead. Should be an instant mileage gain though.

 

[74M35A2]

Ruh roh shaggy that isnt a small cam anymore. It is bound to happen.View attachment 693608View attachment 693609

Sent from my SM-G935P using Tapatalk

That's not yours, it has an $800 electric lift pump on it. Nice fit though, looks stock.

 

[simp5782]

That's not yours, it has an $800 electric lift pump on it. Nice fit though, looks stock.

Thats why i used future tense terminology. Im just waiting for the call to head to Texas

Sent from my SM-G935P using Tapatalk

 

[brazengoat06]

Justbtodaybi installed an egt gauge on a completely stock 8.3 and I was just shy of 1400 on hard throttle trying to keep speed on highway. Keep in mind it's a m934a2 so it's heavy. But still this seemed high for stock. Thinking i should first try and get more air in the engine before doing anything else. Thoughts?

 

[MAdams]

I'm trying to wrap my head around this and an stuck. A few months ago I attempted to advance the IP timing 6 more degrees(14 total) but after I was done I kept wondering if I retarded the timing by mistake. After driving the truck I didn't notice any more power and my EGT's seem high, like 900 degrees F cruising down the street at 35mph. I did the EGT gauge and timing at the same time so I have no base line.

Here's the question. The motor spins CW while looking at the front pulley, so does the IP shaft. Once the IP drive gear is removed from the IP shaft, do I rotate the crank pulley CW or CCW? All the gears under the front cover are throwing me off. Worse case I can go back to stock

 

[74M35A2]

You'll pop the pump gear off like you did, then back the crank pulley up 6 degrees by rotating it counter-clockwise when viewed from the front. Then cinch the pump gear back on.

 

[Mos68x]

How small is the gear on the IP? Once I get tach off, I don't see how I would remove the IP drive gear.

 

[MAdams]

The gear is bigger than the hole. All you can do is use a gear puller to remove the gear from the taper but not remove the gear from the housing, or loosed the IP mounting nuts and knock the IP back a 1/2" or so.

 

[Mos68x]

OK, I wasn't sure if the IP shaft was splined, keyed, or tapered. At least tapered we can adjust timing without removing the whole cover. Now I just have to find the tools since all I have is the standard gear puller, I'll look at HFs steering wheel puller next time I'm in town.

 

[MAdams]

Just a taper, no key or splines. You'll also need some timing tape or you can print your own here. I think the pulley is 8.75? diameter which is 225.25 mm.

https://www.blocklayer.com/timing-tape.aspx

 

[Mos68x]

Another easy way (and free) is to measure the circumference of the damper, which is 30.5625 for mine, divide by 360 for the measurement per degree and then multiply by the number of degrees you want to change the timing. I'm just going to do 8* for a total of 16*. That equates to rotating mine CCW by 5/8~11/16 or 17~18mm

 

[Russ Knight]

Following. Dang you guys are smart!

 

[Mos68x]

Well that was a fail, gonna have to reset it back to what to was and figure out how to set proper timing marks on the crank and then figure out where timing is at right now.

 

[Mos68x]

I was rereading the thread from the beginning, does anyone have pics of their timing pins so that I can go back to a referenced point? I'm at least going to undo what I did earlier

 

[74M35A2]

The timing pins on the pump and engine gear case rear will only depress in at one point each. Pull the pump gear off, rotate each until the pins can each be pushed in, then bolt the pump gear back on. That will set the timing back to the stock 8 degrees. Don't forget to pull both pins back out before starting the engine!

 

[Rmtaunton]

74 ,, you have all the knowledge on this , and now a new motor and 13 speed , still looking forward to both but nobody has done it yet , I might take the plunge , and document it if you can stand lots of emails and do you still have the 6 speed


Sent from my iPhone using Tapatalk

 

[MAdams]

These have been the most helpfull vids.
https://www.youtube.com/watch?v=DIBL4tIF6tE
https://www.youtube.com/watch?v=gwepAWiP_m0

Remember the torque specs on the nut are important

 

[Rmtaunton]

Thank you more info the better!!


Sent from my iPhone using Tapatalk

 

[74M35A2]

6 speed and spare 8.3L is scrapped. Got like $62 for all of it. Would have rather one of you had it, but nobody wanted a 1:1 final gear trans, or to ship the stuff.

Sorry I never did this to mine, but I fully understand how to and would be happy to talk anybody through it. Feel free to fill my inbox, I'll give you my cell #.

 

[Mos68x]

6 speed and spare 8.3L is scrapped. Got like $62 for all of it. Would have rather one of you had it, but nobody wanted a 1:1 final gear trans, or to ship the stuff.

Sorry I never did this to mine, but I fully understand how to and would be happy to talk anybody through it. Feel free to fill my inbox, I'll give you my cell #.

I musta missed that, I certainly would've taken them both, even if I only used the engine.