Low Cost DIY Rod Weighing Setup

FWIW…. Pishta and I have been setting up low cost, home-shop weighing equipment for big and small end rod weights. This is a summary of one setup that is simple to build and repeatable. It is not the ultimate in accuracy but will measure end weights to a few grams tolerance, which is around 10 times tighter tolerance than the standard factory balance tolerance. And with a small expenditure…..

BTW, if you want to see it ‘in action’, skip 3 posts down to get past the theory and build info.

BACKGROUND OF ROD WEIGHING TECHNIQUES:
The standard methods of rod weighing divide the rod weight along the beam axis (the long axis) on either side of the rod's center-of-gravity. The usual devices hang the rod so that the plane of the big end is vertical. You can see these jigs all over the internet, like this:
Connecting Rod Balancing Stand

The rod's big end plane being vertical is done so that the equipment is adjustable and is easy to use, but there is nothing requiring the plane of the big end be vertical; the plane of the big end can be horizontal or at any angle, as long as the beam axis of the rod is accurately held horizontal.

The jig described here is one that holds the rod horizontal on a flat plate, but it works on the same exact principle: support each end on a line across the exact center of each end, with the beam axis level, and then weigh one end at a time. This jig generally achieves a +/- 2 gram repeatability, but is not as fast and convenient to use as purchased hanging setup. So it’s not suited for a pro shop, but for the price a handful of scrap materials, IMHO it works to expectations for a home shop, and gives the accuracy needed for a low-mid range hot-rodder.

NOTE on the scale used: If you are using a cheapo scale, they have ‘issues’ for this type of use regardless of the type of jig or rod orientation. Their readings will be thrown off with miniscule side loads or tilt loads, due to their cheap design (which do not have adequate numbers of electronic load cells to compensate for these loads).

Work-arounds are described for these cheapo scale problems for this flat plate jig, which only creates side loads on the scale, not tilt loads. The ‘hanging rod’ type of jigs put tilt loads on the scale, and that does not appear to be manageable with the cheapo scales.