connecting rod, angle cut cap

dan miller · Post by **dan miller** » Wed Dec 10, 2008 11:36 am

Why do some connecting rods have the cap placed asymmetrically? Looks to be around 45 degrees.

I suppose that it transfers some of the bolt tensile load to shear, and probably allows for a little more camshaft clearance.

But, there has to be more to it than the above. Assuming "the above" is correct. lol

Thanks, Danny

miniv8 · Post by **miniv8** » Wed Dec 10, 2008 11:47 am

Its main purpose is to get the rod down the smaller cylender.

gmrocket · Post by **gmrocket** » Wed Dec 10, 2008 6:14 pm

as in the british leyland A series

MadBill · Post by **MadBill** » Wed Dec 10, 2008 9:16 pm

A friend of mine could have used such rods a number of years ago. He came into a great deal on a bunch of stock block Buick Indy parts and started building up a class-killer engine for a 170 c.i. boat racing class. When everything had been machined and he started bolting it together, he found that the bore he'd had to sleeve it down to was too small to get the rods through...

rustbucket79 · Post by **rustbucket79** » Fri Dec 12, 2008 2:11 am

OOF!! That must have been a sad day indeed.

machine shop tom · Post by **machine shop tom** » Sat Dec 13, 2008 1:48 pm

MadBill wrote:A friend of mine could have used such rods a number of years ago. He came into a great deal on a bunch of stock block Buick Indy parts and started building up a class-killer engine for a 170 c.i. boat racing class. When everything had been machined and he started bolting it together, he found that the bore he'd had to sleeve it down to was too small to get the rods through...

Truly a "DOH!" moment.

tom

jake197000 · Post by **jake197000** » Thu May 12, 2022 2:46 pm

flathead lincoln same way v-12

PackardV8 · Post by **PackardV8** » Thu May 12, 2022 4:01 pm

Many diesel engines, including the millions of Cummins 6-cyls, are this way.

mag2555 · Post by **mag2555** » Thu May 12, 2022 6:20 pm

They also did that to make changing out bearings easier while keeping the motor in place.

Boy I wish some big ass stationary Diesel generator’s that I have rebuilt where that way!

modok · Post by **modok** » Thu May 12, 2022 11:33 pm

Who is they?

jred · Post by **jred** » Thu May 12, 2022 11:52 pm

just got done with a 2015 2.7 v6 ecoboost con rods are that way..

Post by **davidbraley** » Fri May 13, 2022 12:56 am

Sorry if this is a really dumb question...

How does clocking the parting line for the rod cap like what is shown above effect the bearing clearances? It's my understanding there is more oil clearance at the parting line.

modok · Post by **modok** » Sat May 14, 2022 2:49 am

Good question.
Achieving tightest clearance in the loaded direction is one reason, but not the ONLY reason for bearing wall eccentricity.
The other reason is to counteract housing distortion from the bearing interference fit or "crush", so that's unchanged.
And another reason is to make up for flex in the housing, but a rod mainly flexes in a bad way when under tension.

Yeah having the tightest point at 45 degrees is not perfectly ideal, but it's not that bad either. No different than a 90 degree v8.
Many of these are LOW rpm, or diesel engines where the rod only sees high loads of compression, so they do not need a lot of wall eccentricity in the bearing.

Don Terrill’s Speed-Talk

connecting rod, angle cut cap

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