Cummins rod type

[bgilbert]

Is there a certain name for our offset style rods? My bro in law brought this up, when I showed them a pic of the Ford, Chevy and Dodge rod I printed out from this site. He said he was told Mac used or uses this type of offset rod and he was always told it made the rod weak. . ?? Just wondering if anyone can enlighten me here.

 

[HoleshotHolset]

I don't see how an offset rod could make it weak...



I remember reading that the offset is to help out the rod bolts. With the offset angle - the most extreme stress is never parallel to the rod bolts... this reduces the amount they stretch.



Matt

 

[bmoeller]

It also helps to remove/install the pistons.

 

[bgilbert]

I wasn't concerned much about the weakness idea, but I'm told theres a name for that style of rod, I would like to find out.

 

[nickleinonen]

another pic of our cummins conrod as well as 6. 0 & 6. 6 conrods



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[Grey Wolf]

I thought they were just called fractured connecting rods due to there unique construction. I believe Cummins started it, GM and Ford have adopted the same construction.



Here's an article on Navistars process.



http://www.sme.org/cgi-bin/get-mag.pl?&&02dem002&000007&2002/02dem002&ARTME&SME&

 

[Andy Perreault]

Looks like the Ford Powerstroke rod in the picture Nickleinonen posted is of the same design as the Cummins. It's different than the one in Bgilbert's picture.

Andy

 

[nickleinonen]

the only reason really for the offset on the cap on the conrod is to fit a big rod through a small hole...

 

[RonaldLarson]

Holesh0ot's right

The offset was Clessy's design. It is effective at taking the shock of the compression and power stroke off the rod bolts. Less bolt stress and stretch. Besides that interesting fact, our rods are quite larger than the others designs. Cummins' are just stronger from the small details to the overall massiveness. More mains, less crank flex, Etc.

Ron

 

[jwgary]

In all fairness, I think that Ford and Chevy are catching up with the con-rod technology (Ford more so than Chevy) that we have enjoyed for years. You look at the rods in the picture posted by Nick and you can see that the Cummins rod is bigger but not as much as it is when compared to the older versions in the one that bgilbert posted (even though they are labled as the current designs). You can expect the others to be a little smaller since they are using two more cylinders than us. The load per cylinder is less so the rod does not need to be as big. I agree that our layout of the I-6 is much more robust with one more main journal than cylinder as opposed to three less in a V-8.

 

[Breck]

This sheds light on why GM guys always seem to have the "small rod" syndrome; The pictures even prove it true.

 

[RustyJC]

The offset was Clessy's design. It is effective at taking the shock of the compression and power stroke off the rod bolts. Less bolt stress and stretch.

Loads during the compression and power strokes are compressive on the connecting rod, loading the top half of the bearing shell. The rod cap and bolts are just along for the ride during these phases of the combustion event.



The reason for the offset is to allow larger rod journals on the crankshaft by moving the bolt bosses on the connecting rod splitline out of the way so that the piston and rod (less cap, of course) can be pulled through the cylinder bore.



Rusty

 

[pwerwagn]

This sheds light on why GM guys always seem to have the "small rod" syndrome; The pictures even prove it true.

Ha ha ha! Then they'll tell you that a shorter stroke is better too!

 

[mhenon]

That Ford rod actually looks beefier then the Cummins.

 

[Vaughn MacKenzie]

Some comments in response to some of the posts . . .



I don't believe the first photo posted is accurate. Looks like a photoshop job of 2 gasser rods.



The 6-liter rod does look strong and beefy, but if you view the rods on edge the Cummins one will be quite a bit thicker. . . remember the wider rod journals of the I6.



Cummins began the fractured-rod process with the HPCR motor. I believe the DMax featured this from day 1 so I think they had it first. Who was the first to bring fractured-rod cap process to the automotive market? Ford was, in their 5. 4L V8, debuting in the Crown Vic in the early '90s.



What are the advantages of fractured rod caps? The breaks follow natural material grain, and when the caps are bolted and torqued down, the "big end" bore distorts less and leads to longer bearing life, and allows tighter clearances.



Another question to ask. . . what are the rods MADE of? I know Cummins is forged, probably the same for the others. The 7. 3 PSDs had powdered metal process which makes them more prone to failure when a lot of torque & cylinder pressure is applied.



Vaughn

 

[DPelletier]

Yep, the Ford rod looks adequate, but it isn't anywhere near as strong and beefy as the Cummins rod. You can't see the thickness of the rod from that angle and the pic doesn't do the Cummins rod any favours. If you look carefully, you can see the portion of the Cummins rod that is very dark and harder to see. In any event, it is much heavier and just has a higher level of quality to it. Looks like jewelry to me ! . As Vaughn has pointed out, the Cummins uses a forged connecting rod. The 7. 3 PSD used to use a forged rod (up until '99, I think) but since has used a powdered metal rod. The Ford guys use the earlier rods for high HP applications. I had thought that the 6. 0 PSD also used the powdered metal rods, but I am unsure of that. As far as the pics go, I have seen that first picture with different labels before. In that pic, the Ford was a 7. 3 PSD and the GM was a 6. 5TD, so something is not cricket there.

 

[Grey Wolf]

Vaughn,



Cummins has used the drop forged, angle split (fractured) cap to rod in the early "B" engines

 

[Vaughn MacKenzie]

Are you sure Grey Wolf? I had heard the fractured cap process started with the 3rd Gens but I could be wrong. If you will look closely at the Cummins rod in the first picture and compare it to the one here you'll notice the 3rd Gen one has been redesigned (but that doesn't mean the older one wasn't fractured): http://www.nwbombers.com/cgi-bin/forum/ikonboard.cgi?;act=ST;f=5;t=8985;hl=rod

 

[Hohn]

Vaughn,



Cummins has used the drop forged, angle split (fractured) cap to rod in the early "B" engines

Vaughn-- check this thread for great info on the rods:http://www.dieseltruckresource.com/...=502382&highlight=rod stroke ratio#post502382



Don M shows the pics and describes the differences in material and capscrews used over the years...



Justin

 

[Grey Wolf]

Vaughn



My information was from a Cummins brochure that I picked up at the 1983 International Truck Show held at Los Angeles. The “B” was introduced at the show this year. It does refer to the angle “split” cap to rod interface, however after looking at an old rod in the garage the mating surfaces have been machined. The rod cap surface doesn’t have the rough grainy look of the “Fractured” rod. So although they appear the same, they are not the same, evolution I guess.



I might add, at the time, I thought the engine would be a nice candidate for an engine conversion.