Forged vs. Cast Con Rods

[Clem Z.]

Re: Forged vs. Cast Con Rods

cracked cap rods have been used for years in 2 cycle engines as i have go kart engines from the 60s with cracked cap rods. these 2 cycle rods are hardened for use with needle bearing.

[John H.]

Re: Forged vs. Cast Con Rods

The PM rods require very little machining, and almost none for balancing, as there is virtually no weight variation part-to-part; the "split line" is scribed first with a laser, then they're "broken" in a hydraulic fixture.

[Mike McKown]

Re: Forged vs. Cast Con Rods

Didn't have a clue what the manufacturing proces was for a "cracked rod" was 'til I read this post. Matter of fact, didn't even know what a cracked rod was unless it was poked through a cylinder wall.

Please enlighten those of us in this boat that wonders how a "regular" rod such as a 327 rod is manufactured. I'm sure some out here would like to know.

Thank you,
Mike

[John H.]

Re: Forged vs. Cast Con Rods

Mike -

Traditional GM forged steel rods start out as a red-hot steel billet slightly larger than the rod - this billet goes through three or four hammer-forging dies in a forging press, and is progressively formed to shape by each blow of the press through the set of dies. When it comes out of the last forging die, which trims the forging flash at the die parting line, it's quenched in water or oil and moves on to machining. The big end is literally sawn in half horizontally to separate the cap, the sawn mating surfaces are machined flat and the rod bolt holes are drilled, both halves of the big end are rough-finished including the bearing tang slots, the rod bolts are installed, and the caps are mated and bolted to the rods. The assembled rod then goes through another machining process to bore and finish-machine the pin end and the big end, and another machine weighs it and grinds the balance pad to get the weight within spec. The rods are then mated to an engine set of pre-ringed pistons, the bearing inserts are installed, and the caps are re-installed and tightened to seat the bearings. The nuts and the caps are removed, and that set arrives at the engine assembly line on a conveyor in a compartmented tray. After the piston/rod is "stuffed" into the block, its companion cap and nuts are installed and torqued. The piston-stuffing operation was something to see on the #1 line at Flint Engine, which ran at 170 engines per hour (the #2 line ran at "only" 100 per hour)