What is weight of stock 340 piston

pishta said
trick is to get a good big end weight with any DIY jig. The varience is unbelievable with the smallest bit of pivot movement on either end. I bet that pro jig in all the videos would give a different weight with the slightest amount of skew in the horizontal plane. I ended up using a ball bearing in the little ends rod bushing so it would find its highest point horizontally and using 3 ball bearings under a metal plate to support the big end at a perfect 90 degree on the scales plate. That way the lateral position was always the same with no x-axis force, and still could only get 2-3g repeatablilty. Cheap scales dont handle side to side force well when looking for repeatablilty. straight weight is eazy, highly repeatable on even the HF .1g scale. 4 of 5 weigh ins on a piston will give me the same .1g result with 1 being .1g off. sometimes just tapping the table will get it to fall in line with the others.

Yep, I tried all sorts of techniques to get the side load error out of my $50 scale.....I tried a sub-plate on the scale on oil of various weights to relieve the side load error... 75W90 gear oil was the best. But it still had several grams of variance in repeatability. Finally, finding the area to tap on the machinist's flat that supported everything to make thing 'settle in' did the trick. Ended up with a +/-1 gram consistency on the big end. Even with that, the sum of the small and big end weights average about 1 gram below the total rod weight by itself so there is probably a small uneven-ness somewhere.

My setup is on a machinist's flat, and is carefully leveled in both axes. I took a lot of care to get the measurement plate even and level, and symmetrical in weight, but it it probably still off a hair. It is the hardest part of a DIY balance process. I just checked a fresh batch of SCAT rods on my setup and got their numbers within +/- 1 gram.. at that point, I could not say if it was the setup of the normal rod variance.

This is a balance machine mfr's series of intro/training videos and when they do the big end weights, they either have a really repeatable setup, or they are more casual than expected in measuring big ends weights. Their vertical suspension rod weight scale is interesting; it is in part 3 or 4.