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Discussion Starter #1
Hello, has anyone reduced the diameter size of a stock p30 flywheel? I'm wanting to match the flywheel diameter to my stock nsg370. I realize that it would need to be balanced. My plan is to have a machine shop then make my engine to tranny adapter. This is a 2007 JKUR project with a 4bt cpl#0858 stock with only minor modifications for longevity only. It seems since the 07 and newer nsg370 isn't used for this type of conversion that information is very limited. Any assistance would be appreciated

Thanks

Tony
 

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Are you sure you want to run that transmission with a 4bt? A bare bones stock 105 HP 4bt has 265 lb ft torque output. The max on the NSG370 is 272 lb ft. You're basically at the limit point. Are you planning to make a custom transmission adapter? By reducing the flywheel you are making it lighter. You might be creating even more engine vibration than it already has.
 

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Discussion Starter #3
Yes I have already contacted a local CNC machine shop and he is very confident that he can make the adapter. One of the biggest reasons I'd like to stay with the factory transmission is due to the ease of conversion, ability to use factory transmission mounts/drivetrain components etc. This Jeep will basically be used for Sunday driving 🙂. I have other vehicles for off roading and anger management.. I have no intention to create additional hp so I think the tranny would be adequate under these circumstances. So figuring out which flywheel to use or alter is going to be a task. I'm just not that familiar with they way the way the trans works, what considerations need to be made like tolerances for the clutch to flywheel. So once I get the flywheel figured out, I'll need to address the adapter thickness. I appreciate your or any other input. I'm really in no hurry but would like to complete this conversion next year sometime.

Thanks
Tony
 

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Your CPL858 engne is the 105 HP version with the VE injection pump. Your transmission replaced the NV3550 which had a 300 lb ft torque rating. Those didn't like being behind a 4bt either. You'll just have to be gentle with it. What size will your clutch be? All that torque on a Cummins hits around 1700-1800 RPM.
 

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Discussion Starter #5
Thanks for the information! I think the existing flywheel will accommodate a 11" clutch. Still not sure if it will all work, don't know if I can find a compatible flywheel? Can mine be machined to work? Tolerances/measurements? Still a lot of unanswered questions.
 

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Thanks for the information! I think the existing flywheel will accommodate a 11" clutch. Still not sure if it will all work, don't know if I can find a compatible flywheel? Can mine be machined to work? Tolerances/measurements? Still a lot of unanswered questions.
The Cummins/Ford adapter use a clutch disk that is compatible with the jeep input shaft, I'm not sure if the pressure plate has the right standoff for the NSG's slave cylinder to work but if your making the adapter itself then Id "think the Cummins/Ford flywheel might be what you could start with. I'd think it would be easy to machine one for the NSG's ring gear.
 

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Discussion Starter #7
Thanks! Another obstacle, I just spoke to our local electrical shop and was told that the Jeep/factory starter probably will not start the 4bt Cummins! Any thoughts on this? I was told also that the starter could not be altered to the 2.0/2.5 kv required. Still researching!!
 

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It takes a lot of torque to spin a diesel. Gas engine may have had about 9:1 compression ratio and the Cummins around 17.5:1. Also the battery cables and battery or batteries have to be up to the task. You usually want the positive and negative cables to be 2/0 gauge which is near 3/4" counting the cover where the Jeep might have been 4 ga or 6ga which is tiny stuff. And yes, the OEM diesel starters are usually a chunk. Not sure what you'd do for that.
 

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Thanks! Another obstacle, I just spoke to our local electrical shop and was told that the Jeep/factory starter probably will not start the 4bt Cummins! Any thoughts on this? I was told also that the starter could not be altered to the 2.0/2.5 kv required. Still researching!!
I have a Jeep flywheel for the NSG and a Cummins ford starter on the shelf, I'll dig them out to see it the pinion gear pitch is compatible with the Jeep ring gear if it is then all you will need to do is the math to get the right standoff and lash for mounting it to your adapter.
 

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I had the 7.3 when running the Cummins/ford adapter the diesel ZF adapter uses the 6.0 starter. the 7.3 and 6.0 are very close in dimensions.
The starter I have on the shelf is the factory one for the cummins/Ford setup.
 

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The Cummins/ford starter is NOT compatible with the jeep's NSG flywheels ring gear..:(
 

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I think I would see if I could get the Cummins/Ford flywheel to work within the bolts and dowel pin locations of the Jeep/AMC bell and if so just locate the Cummins/Ford starter where it will engage the ring gear on the Cummins/Fore flywheel.......
AMC_bellhousing_bolt_pattern.png
AMC_bellhousing_bolt_pattern.png
 

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Discussion Starter #14
I appreciate everyone's input! The 07 and newer nsg370 has a integral bell housing which in my opinion is the biggest downfall for my project. I have a backup plan just in case. I have a 1998 nv4500 from a Dodge used behind a gasser. I really wanted to stay with the 6 speed but, I guess some more research and time will tell.
 

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You'd have some issues to work out with the gas NV4500 as well. There weren't any adapters for the 4bt for the gas Dodge bolt pattern. You have to use an SAE adapter from Phoenix Casting to mate that one to an SAE3 Cummins block housing. The Cummins NV4500 has a different bellhousing and larger input shaft,
 

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Discussion Starter #16
Thanks, the nv4500 that I have didn't come with a bell housing or tail shaft. I'll have to check out Phoenix.
 
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