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3.9L cummins in Jeep Wrangler??????

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3.9L cummins in Jeep Wrangler??????

ArizonaPerfect ArizonaPerfect
New User | Posts: 22 | Joined: 07/08
Posted: 02/19/11
06:40 PM

Okay, I made my first attempt to install balance shafts into my 4BT.  Things did not go good.  I ordered the mounting bolts from Cummins.  As soon as I pulled one out of the box I knew they were wrong.  I've never seen a main cap bolt with fine threads.  I double checked the parts book and part number on the box and everything seemed right.

Since pulling the oil pan is a total no-brainer, and I needed an oil change anyway, I decided to pull the pan and see what kind of main cap bolt is in the engine. The main cap bolt in the engine is a M14 x 2.00 with a 12 mm shank and a 23 mm head.

The Cummins bolt (3927949) that is to be used to install the balance shaft assembly is wrong.  The bolt length is correct, but the threads are M12 x 1.50.  So that is not going to work.  So I put the original main cap bolt back in and reinstalled the oil pan.

For those who have never seen a 4BT balance shaft system, the balancer assembly bolts to the bottom of the number 1 and 4 main cap.  The original main cap bolts are replaced with a much longer bolt.

Does anyone out there know of another Cummins part number for a M14 x 2.00 x 231mm Grade 12.9 main cap bolt?  The 3927949 bolt is not the correct.

Once I get past this main cap bolt issue, the rest of the installation looks good.

More to follow.........  

jakethejake jakethejake
New User | Posts: 1 | Joined: 02/11
Posted: 02/20/11
06:53 PM

I also want to stick a 4bt in a wrangler here withing the next year or so. I am gonna start gathering parts and info now so that the difficulties in the near future are smaller and fewer. is there anyone here who'd be willing to submit themselves to constant bombardment from my questions?  

ArizonaPerfect ArizonaPerfect
New User | Posts: 22 | Joined: 07/08
Posted: 02/28/11
05:24 PM

After some serious digging I found the correct balancer mounting bolts.  The Cummins part number for the bolts is 3904218 (M14 x 2.00 x 231mm long/Grade 12.9).  So at this point I think I have everything I need to install the balancer assembly.  The plan is to install it this weekend.  I'll write with results after I do the installation.

More to follow........  

ArizonaPerfect ArizonaPerfect
New User | Posts: 22 | Joined: 07/08
Posted: 03/06/11
05:03 PM

The installation of the balance shaft assembly happened this weekend without any problems.  The new main cap bolts fit perfect.  Timed the balance shafts to the crankshaft as per the service manual instructions.  It's a pretty simple process.

I did have to modify the oil pan slightly to gain enough clearance for the front axle.  Nothing a little cutting and welding couldn't fix.  Adding balance shafts does require a lot extra clearance for the balancer assembly and oil pan.  My Jeep has a 6 inch lift and I would say that is the minimum lift to get everything to fit. well does it work?  In one word, FANTASTIC!  The engine is about 90% smoother than without the balancer assembly.  There is still a slight amount vibration that I would consider normal for any engine.  The big gain is that there is no more blurred mirrors, buzzing dashboard or steering column.  All that frequency induced vibration/buzzing is gone.  The engine seems to be in total harmony with itself.

Anyone who plans on doing a 4BT Cummins should get the balance shaft assembly.  It make the engine much more civilized.  There happens to be a balance shaft assembly for sale on eBay right now.  The item number is 300483171630.  Punch that number into the search bar and it should come up for you.  That is only the second balancer assembly I've seen for sale in 4 years.  The first one I saw for sale I bought.  I got a great deal ($500.00).  

Cummins has brand new balance shaft assemblies for $2,800 dollars.  That was a little steep for my budget.  So I just waited for something to show up on eBay.  

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