Milodon 440 Chrysler Main Cap Upgrade

INSTALLING MILODON'S NEW BILLET STEEL CROSS-BOLTED MAIN CAPS ON A MOPAR 440 BIG BLOCK
As part of our upcoming Mopar 440 stroker build, we felt it necessary to upgrade to billet steel main caps. Luckily Milodon was just coming out with it's newly redesigned steel caps manufactured to accommodate the installation of "Hemi-style" side cross-bolts. According to Milodon President Steve Morrison, the caps are available for both the 383/400 B blocks and the 440 RB blocks and they incorporate an improved steel alloy for additional strength. Morrison also explains that unlike most caps these are configured to accept larger 3/8-inch cross-bolts instead of the more typical 5/16-inch bolts. They take a bigger bite of the cap material and form a very rigid structure around the crank.

We had a choice between stock mild steel, ductile iron and aluminum; the characteristics of each which are widely debated among racers, engine builders and manufacturers. We chose Milodon's billet steel caps for maximum reliability. The cross-bolting feature is attractive and Milodon's machining procedure for the main web braces offered a good approach to maintaining strength. Cross-bolting is a considerable plus in the effort to prevent main cap walking, a problem often noted when upgrading or rebuilding performance  applications. Main cap walk is caused by the crankshaft being forced downward, overloading the factory main caps and  fasteners, altering main bearing oil clearances, and allowing the crank to wiggle and flex to the point of bearing failure.  Not all shops are equipped to handle the machining requirements so we chose one of the best around, QMP Racing Engines in Chatsworth, California.
We acquired a crack-free 440 Chrysler block that had never been bored. It pressure tested successfully and cleaned up well prior to the new main cap installation. But first some basic machine work is in order.
Here, the initial set up and measurement verification is being performed by Brad Lagman at QMP Racing. In the photo on the right Brad is determining the crank centerline from a known standard so he can program the CNC cutter for the side rails. The side rails must be machined equal distant from the centerline to ensure an accurate line boring operation.

The cap registers are measured and machined flat to the lowest register. Minimum material is removed to prevent adding slop to the timing chain assembly.  Use a bottoming tap (top right) to ensure that all the threaded holes are tapped all the way to the bottom. A tapered tap (bottom right) reduces the thread cut near the bottom. It can cause main bolts to not fully torque, thus losing clamping force. Or it can cause unequal stud seating and thus stud height which can cause interference with some windage trays and affect the way the studs engage.

The illustration to the right shows how the last three or four threads are tapered. A main bolt can jam up against those threads making the threads above it useless to the clamping load. Those same tapered threads will prevent a stud from fully seating causing the same problem. Studs are typically installed finger tight so you have the stud jamming up against a few threads at the bottom which may allow it to cock and prevent the threads above it from engaging properly for optimum clamping force. It is important to get this procedure right because you want the new caps to be properly registered with full clamping force before you drill the block and caps for the cross bolts. When done correctly, all of the studs should protrude the same height above the nuts and washers. When tapping, make sure to work the bottoming tap in small cuts and clean it often so you establish evenly cut threads all the way to the bottom.

The inside of the pan rails must be CNC milled to exactly 8.000 inches wide and 1.500 inches deep to accommodate the cap wings. This requires a cutter with at least a 0.060-inch radius edge. Pick up the center line of the main bore to move out exactly 4.000 inches to either side. Or pick up the cap register to move out from. If you use the cap register method, remember that the tang side of the cap is factory offset 0.060-inch from the non-tang side. When this step is completed, and the machining debris is cleaned up, install all five caps with bolts or studs and torque to 85 ft/lbs with oil. Bolts are provided in the kit, but we chose to use the optional stud kit, PN81180 to ensure maximum clamping force. QMP Racing now marks the caps with numbers and small arrows indicating the front of the block.
With the pan rail modifications completed and the caps installed it will look like those in the adjacent photo. The caps fit snugly and are firmly captured by the cap registers and the machined side of the block. Using a mill, we are now ready to drill the block and caps for tapping. Milodon caps use the same location as the original 426 Hemi. The cross bolt holes  center on the caps and are positioned 0.875-inch down from the pan rails. This ensures that no cross bolts interfere with existing threaded oil pan bolts.  The cross bolts will pass above the oil pan bolts. Note that much of the original side supports for each main web still remain and there is some space still open to accommodate bay to bay breathing in the deep skirted block.
The cross bolt holes are drilled 2-3/8-inch deep with a .3125-inch drill bit through the block. Make sure they are centered on the main cap. Tap 3/8-16 threads to the full depth on each cap, then remove the caps and spot face all the holes to accommodate the cross bolt washers. Then enlarge the holes in the block to 0.375-inch to accept the bolt shank. The 3/8 grade 8 bolt has huge shear strength and is minimally invasive to the block.
Milodon's caps are attractive because they make engine specific caps for both the B and RB series engines. "B" engines, (361/383/400) and "RB" engines, (413/426/440) have different size main journals, so each will have a different size main bearing. The "B" engine has 2.625" mains while The "RB" uses a 2.750" main journal diameter as is the case with our 440. Through 1973, the diameter of the thrust surface's outer edge (#3 main) is smaller, 3.470" on the "B" engine and 3.600" on the "RB" engine. From 1974 on, the diameter was increased to 3.750" for the "B" engine and 3.880" for the "RB" giving the thrust face more surface area for heavier duty use. Many aftermarket caps are made only for the 383/400 B engine blocks forcing machinists to make many small passes to prevent the align bore from going astray and departing from the true centerline when opening them up to the 440 main size.. Some manufacturers say this is no big deal, but it raises the cost of machining time and, depending on the equipment being used, it risks inaccuracy which can lead to undesirable consequences.
Here are two views of another brand aftermarket aluminum cap made only to fit "B" engines. There are no cross-bolts on these caps. Note the mismatch at the parting line when installed on a "RB" block. As seen in the second photo, the machinist has to make numerous small cuts to open up the housing bore on the cap to match the housing bore on the 440 block. If you're not building a 440, these "two-bolt" caps are probably sufficient for the 500 horsepower range on street engines, but the billet, purpose fit Milodon caps are definitely more desirable for higher power levels on any size engine.

Milodon Billet Main Caps    (Cross-bolt Design)
426-440 RB Wedge, 4-bolt  (5 Caps)
426-440 RB Wedge, 4-bolt  (3 Center Caps)
383-400 R Wedge, 4-bolt     (5 Caps)
383-400 R Wedge, 4-bolt     (3 Center Caps)

Available through www.summitracing.com under these PN's
Click PN to go to the Summit page.

Main Cap Set
PN 11365
PN 11360
PN 11362
PN 11361
Main Cap Stud Kit
PN 81180
PN 81180
PN 81180
PN 81180

Milodon Billet Main Caps    (Cross-bolt Design)
426-440 RB Wedge, 4-bolt  (5 Caps)
426-440 RB Wedge, 4-bolt  (3 Center Caps)
383-400 R Wedge, 4-bolt     (5 Caps)
383-400 R Wedge, 4-bolt     (3 Center Caps)

Available through www.jegs.com under these PN's
Click PN to go to the JEGS page.

Main Cap Set
PN 11365
PN 11360
PN 11362
PN 11361
Main Cap Stud Kit
PN 81180
PN 81180
PN 81180
PN 81180

SOURCE

Milodon Inc.
2250 Agate Court
Simi Valley, Ca 93065
(805) 577-5950
https://milodon.com

QMP Racing Engines
9530 Owensmouth Ave. Suite #2
Chatsworth, CA. 91311
818 576-0816
www.qmpracing.com

 

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