nm9stheham
Well-Known Member
I was taking apart some older, original 340 rod/piston assemblies, and after clean-up, did a quick visual on the rods; PN is 2899496. I had to do a double-take to see if I really saw what I initially thought I saw.
I spotted a 'squiggle' in one rod casting when looking along the side of the beam. 'So there's a bad one'...... But then, a close look at each rod showed the same thing. 4 all had one casting number and showed the same 'squiggle' pattern. The other 4 had a different casting number and showed a different but consistent 'squiggle' pattern.
I did a quick check for offset between big and small ends, and a quick measurement showed that there is a consistent offset of between .030" and .040" towards the large chamfer side of the big end. But most or all of this is from the way that the big end is ground asymetrically. Plus, the wear and varnish patterns were very symmetrical side-to-side on the pistons and pin bushings, and the rod bearing upper shells showed what I have seen to be normal wear patterns in other engines. The machine marks on the sides of all of the rod big ends are all still clean and essentially unworn, so the big ends have not been twisted against each other or the side of the journals.
So I can't tell if this 'squiggle' is real or is just a casting irregularity. Were these just erratic castings back then? I have never spotted such a thing in other rods. Is this what made 340's so quick? LOL
Here is a pix below; notice that the edge of the beam looks to turn slightly left above the big end, and then turns slightly right about an inch below the small end. A straight edge confirms this squiggle is really there.
I spotted a 'squiggle' in one rod casting when looking along the side of the beam. 'So there's a bad one'...... But then, a close look at each rod showed the same thing. 4 all had one casting number and showed the same 'squiggle' pattern. The other 4 had a different casting number and showed a different but consistent 'squiggle' pattern.
I did a quick check for offset between big and small ends, and a quick measurement showed that there is a consistent offset of between .030" and .040" towards the large chamfer side of the big end. But most or all of this is from the way that the big end is ground asymetrically. Plus, the wear and varnish patterns were very symmetrical side-to-side on the pistons and pin bushings, and the rod bearing upper shells showed what I have seen to be normal wear patterns in other engines. The machine marks on the sides of all of the rod big ends are all still clean and essentially unworn, so the big ends have not been twisted against each other or the side of the journals.
So I can't tell if this 'squiggle' is real or is just a casting irregularity. Were these just erratic castings back then? I have never spotted such a thing in other rods. Is this what made 340's so quick? LOL
Here is a pix below; notice that the edge of the beam looks to turn slightly left above the big end, and then turns slightly right about an inch below the small end. A straight edge confirms this squiggle is really there.
