Mike D

I didn't know the rods were powdered metal! I thought they just went to an H beam and that was it.

Bean

They are still a I beam but PM cracked cap's. Used to those in PSD's breaking at about 400hp. I believe all of the new engines from 03 on are cracked caps.

JDGnut

Beam.. the cracked caps is just the way to identify the powered metal rods?? The Just off topic... what is powered metal??

lmills

cracked caps started in late 04 if memory serves me correct

PourinDiesel

They started back near the introduction of the CR engine. However some of the early CR's used the old style rod for while.......

Don M

Hang on. The CR rods are not powdered metal. They are a forged steel rod.

Yes, the cap is cracked, but the alloy is "C70 steel microalloy". It is a ton stronger than a powdered rod but can be used in a cracked cap design.

They are stronger than any other rod Cummins used in the 5.9. Ever.

The 6.7 breaks rods because of the stroke length and rod angularity.

BCB

sorry but what is a cracked cap design?

Bean

Everyone I have talked to thinks that the older style rods are stronger and hold more hp. What makes the Cr rods IYO better then the older rods?

Don M

Hey Bean,

The CR rods, the 12V rod, and the made in England and Mexico 24V rods have all been lab failure tested. The CR rod was the best.

Recall that a cracked cap design adds a ton of strength in that area. It is much less likely to fail and the fastener has a better chance of holding up.

All the rods share an 11mm size fastener but the 12 and 24V rods have a double waisted area in the shank. Some guys complain the stock bolts are stretching at higher RPM and the cap is moving around, causing failure. They are upgrading the fasteners. With a cracked cap rod, you dont need that as quickly.

Since we have now seen rod failures in the 6.7, a better rod is needed. And a better fastener as well since the aftermarket rods are not cracked cap. The Cunninghams are "diamond locked" though. I dont know what fastener is being used in the Cunninghams. MP35 would be nice. 625 too.

Mercedes, BMW, and nearly all the European high RPM performance engines are using the forged steel C70 microalloy rods. With a cracked cap!!

Bean

I can see the cap being stronger and the fastener as well but what about compression? Seems like the CR rods are bending alot more then old rods. If thats the case why couldnt we dress up the older rods with better fasteners?

lmills

I keep hearing of rods bending, but never any names. Who has bent them?

Don M

I dont know anyone who has bent a rod in the CR other than Reb. That was a result of the 6.7 stroke, over 1000HP, and high compressive force.

BTW, the CR rod is more resistant to compressive force than the other stock rods by a large amount.

In this order:

Cunningham or whatever aftermarket rod you like
CR rods
2nd gen rods ( 12 or 24 )


If anyone is building a 6.7 for high power, better get Cunningham or equivalent. Might want to check with them on what the fastener strength and size is too.

When I built my last 3 5.9 engines, they all got CR rods, stock fasteners hand picked by hardness and TQ'd to a final of 73 ft lbs using torco assem lube. I have no regrets on that choice of parts. But, I would not do that with a 6.7. Cunningham or similar only. Thanks to Reb, we have a real world, hands on failure number with the 6.7. Around 1000 HP. He proved that one twice. In less than 10 days. LMAO Good enough for me.

lmills

Don't forget the poor power steering pump Don!

LOL

Bean

Thanx for the 411 Don, lookin into aftermarkets right now cause I dont want to give up on the 6.7 setup and shooting for well over 1k with this build. I will be talkin to John about inj setup for it so expect some 03 injs from me soon.

Mike D

Basically, crackable powder steel or C70 steel is used so that the rod caps are separated from the connecting rod in a way that the mating surface doesn't require further machining. Saves money in the manufacturing process.