[leeroyhobbs92]

So i have alot of questions so im just gonna jump into it. I'm installing a 4bt 3.9 into my 91 YJ. I stupidly jumped on the first 4bt I came across that I could afford. So it has the Lucas injector pump. Which I'll obviously change out. From what I've learned from the research I've done so far I'm gonna go with the VE-pump. Can I use the same injector pump drive gear?
On another note. I ordered the rebuild kit that comes with sleeves, pistons ,valves the whole sha-bam. And I received a message from the seller, asking the measurement of the combustion chamber. So what I have is the 45mm. can I go up to the 50mm since I'm running a bigger pump and planning on maybe stage two injectors?(....waiting to be bashed on that comment.....)but keep the crank and for now the cam. I'm also thinking of using the HX30 turbo(....waiting for yelling and cussing...) and I'm wanting to get the bell housing adapter to be able to run the ax15 transmission along with the rest of my drive-terrain.

So this is all on paper right now..well kinda.
I have the motor taken apart down to the block and crank, cam and gearing is all still bolted up. So please guide me my fellow fabricators, mechanics and guys who know more than I do.

 

[stpackard]

You might verify that you have injectors matched with the right pistons and injection pump. Not sure but a genset 4b (non turbo?) might have different pistons than an on road 4bt. Could need to plan on the expense of sourcing parts for a conversion from a genset 4b to onroad 4bt, unless you are goin to try just running as is.
I had to look up /source parts for CPL 0858 (intercooled VE) because mine was originally a skid loader 0730 CPL.

 

[irhunter]

To the OP: Have you read the threads on converting a 4B to 4BT?

The pic of the ID plate is hard to see...the flash reflected.

Welcome to the site.

Roy

 

[leeroyhobbs92]

 

[leeroyhobbs92]

so apparetntly I have 59mm piston/chambers and the kit that I purchased choices were 45mm 48mm 50mm but the seller said that he had what I needed so well see on Jan. 10th when the parts come in. so I'm assuming that I'm in the clear to run the same pistons if I have to even though there was some scaring on the top lip . but that would be above the piston ring so no compression should be loss. Now I'm just left with buying a injector pump really. because the one on it is for a tractor application.
im wanting to go balls to the wall with this build but I have to keep reminding myself that its going in a jeep and I'm wanting to use my stock ax15 transmission. so ill have to stay away from the P pump. but I'm still wanting to buy bigger injectors and run the bigger turbo. but I'm guessing I need to change the head studs since they're probably not rated for that much compression. but idk

 

[irhunter]

Have you read this:

4B3 non turbo conversion to 4BT

Hey guys, I would like to build an expedition car based on JK Wrangler Rubicon, but I don't like the original V6 gasoline engine. As I love Cummins diesels and the 4BT looks to me as a perfect power plant for the JK I'm trying to find one. And I did. It is 3.9 4B3. If I can read correctly what...

www.4btswaps.com

And, have you checked for piston cooler oil nozzles?

 

[stpackard]

If you ordered a rebuild kit based on ESN, that kit might get you set up pistons wise to rebuild to the generator 4B spec, which might not be what you’re wanting since you seem to be wanting an on-road 4BT. I’m guessing most of your kit parts would be the same. I’m not recommending necessarily McBee but they have in their catalog a section based on what kit to order for CPL. Fwiw.

 

[leeroyhobbs92]

I gave that link a quick read thank you for that. So I need to check for the piston oil jet which I'm assuming they mean the holes that line up on the crank with the piston rod to shoot oil through. The bearings have the holes and I remember seeing the hole when I took it apart.

I do have a new question (there may be over a million before thus build us done). So my kit came today. New everything valves, cylinder liners, pistons, bearings, gaskets. So the cylinder liner is rough on the inside. I'm guessing from the lathe or something similar. What am I supposed to do about that? I tried seeing if the piston would slide in and it does not. And I believe those tiny ridges would eat my piston rings alive. So is that a liner that I'm supposed to hone myself or anyone know what I'm talking about?
Also heres a pic of the new piston. I believe the combustion intention on top is bigger than my original but that sounds like more combustion more boost to me really.. and I believe the pistons have the oil jets the post was referring to because there are the holes for the oil piston ring cut into the piston and like I said I remember seeing a hole in the rods end I believe I did(how else would oil get to the piston oil ring?
Im still full throttle on this build i just hope i dont eat a brick wall at some point.....
thank you all who've offered their two cents. I welcome all the advice and expertise i can get

 

[char1355]

Well, this is the second 4B to show up recently. First off, your new pistons are for a 4B. They will not work with a turbo. Wrong type rings. Your pistons are like the first photo below. The second photo shows the correct piston for a turbo engine. They have a special keystone ring at the top to handle the extra pressure from the turbo. Your engine does have the piston cooling nozzles so you don't have to worry about that. I looked at your block on Quick Serve and it has them. You need the turbo exhaust manifold, oil feed, oil drain, and of course the turbo. An HX30W or Super HX30W would be good choices. On the injection pump drive gear the Lucas and Bosch gears are different. I can give you the correct part numbers for any parts you may need. You may, and I emphasize may, be able to reuse the injection lines. That's a bit iffy. You need the VE pump, drive gear, support brace, air control line, and fuel lines. Can't tell what all you might need without more photos. Also, which VE pump do you plan on?

 

[irhunter]

So the cylinder liner is rough on the inside. I'm guessing from the lathe or something similar. What am I supposed to do about that?

and I believe the pistons have the oil jets the post was referring to because there are the holes for the oil piston ring cut into the piston and like I said I remember seeing a hole in the rods end I believe I did

So, as you may know, most large Diesels come from the factory with cylinder sleeves. Changing them out is part of every major overhaul. But that is not the deal with Cummins B-series motors.

For our motors, you pull the pistons and measure/assess the size and condition of the cylinders. You might need a re-hone and standard size pistons. Or, you might need to bore the cylinders and order over-size pistons.

It seems uncommon for people to machine theses blocks to take a sleeve. But, one could. You would bore the block, install sleeve, and then bore the sleeve to take an original size piston. And, by "you," I only mean you, if you are a machinist.

Oil jets attach to the block and squirt oil on the underside of the piston. Char says you have them...you'll see them when you have the oil pan off the motor.

Watching this guy's 6BT rebuild videos might be time well spent:

Roy

 

[char1355]

Cummins pistons for these engines came in STD, +.50mm, and +1.00mm. Above 1.00mm they offered a sleeve in STD size.

 

[leeroyhobbs92]

I just wrote yall a long message getting yall caught up with where I'm at and someone called and the whole thing erased it's self. I learned how to save my message though lol.
So the guy I bought my kit from was so against me sending back the kit that he's allowing me to keep it plus giving me 300 dollars. So I got the gaskets, sleeves, and valves. Just need the correct pistons now.
Hey Char is that part number above the correct piston the right number? I think I found the right ones I'm gonna send yall a picture before I order them.
Oh yeah so Char1355 you were asking me which VE pump I want. I'm about to sound ignorant but I was thinking there was only one type of ve pump. Saying that out loud in my head makes me feel real ignorant. Which would you get. Considering price and performance. I'm mostly going to be keeping it on roads posted at 55 miles per hour and in the woods and on the trails. If that helps determine the right pump at all. Thanks for all yalls input. I'm glad I'm not doing this totally on my own.

 

[leeroyhobbs92]

Is this the correct piston to run?

 

[leeroyhobbs92]

Or this one

 

[irhunter]

Do you have the pistons out?

I don't think you want to buy pistons until you have measured the bores.

Roy

 

[char1355]

In you piston photos, that second piston is not for a 4bt. That is for a QSB 4.5 common rail engine. They have a different bore and stroke than a 4bt. In your first photo, for some reason they don't show the top of the piston. Saying it fits a 4bt covers a lot of ground. Pistons came with different combustion bowls depending on injector spray angle. Agree with Irhunter, you don't buy pistons until you determine what overbore is needed if any.

 

[leeroyhobbs92]

I agree with that. And was also thinking along those line myself recently, and I think I've decided to go with the 1.00mm over bore and take the motor to have the crank turned and also get them to bore out the cylinders and if the stock liners can't go to 1.00mm to get the slope out of the side then the choice would be to install the new liners after they have also been bored 1.00mm over(since they are apparently bore to specification ready make them to the 1.00mm bore so I can get a move on this project buying the rebuild kit with the wrong pistons have really sat me back. So what does everyone think of my plan?

 

[edpruss]

No liners in BT engines!

Ed in CO

 

[irhunter]

So what does everyone think of my plan?

Any plan which is developed before you have the pistons out, and the bores measured, is premature.