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When weighing the pistons and wristpins does anyone have any tips on what kind of scales to use.

Tom Jones
Onex #133
Aerovee turbo

Hello Tom,
I used an electronic kitchen scale and ended up with three pistons with exactly the same weight, one was 5 grammes off.
Installed the lightweight piston on the flywheel side to limit the impact of vibrations on the propeller bearing.
Ran my engine for the first time yesterday evening on a self made test stand, started on the second try.
Regards,
Dirk
OneX 117

Hi Tom,

I used a cheap gram scale from Harbor Freight to weigh pistons, wrist pins, and rods. They were all very close and I simply matched everything up so each set was nearly identical in total weight. Worked great!

Dirk, Mike,
Thanks for your responses. I weighed the rods before installation on a scale that weighed to one gram. They were the same weight and I went ahead and installed them and sealed the case halves. I bought a small electronic scale on Amazon that measures to .1 grams. Wrist pins appear to be identical in weight to a tenth of gram. I have two pairs of pistons in terms of weights. The heavier pair is about 5 grams heavier than the lighter pair. Weights within the respective pairs are only different by less than a gram. I'm thinking to put the pair with the least difference in respective weights on the prop end and the pair with the largest spread nearest the flywheel. I think that may mean the heavier but more closely matched pair winds up on the prop end. Do either of you (or anyone else) see anything wrong with that idea?

Hi Tom,

I think your plan is a good one. With weight differences being so minor I think you'd be fine regardless but matching the two closest pairs and offsetting them such as you described should work well.

Best of luck on the engine build!

Tom,

Perhaps I am exposing my ignorance here but, if your wrist pins, clips, con-rods, rings, etc. all match in weight... is there some reason why you would not file the heavy pistons down so they all matched too???

Aloha,

I stacked up washers on the scales to equal the difference in weight of the two pairs (about 5 grams). It's a lot of metal and I did not see a way that I was comfortable with to remove that much material. After unsucessfully trying to take off less than a gram from one piston of the lighter pair I gave up. Like I said 5 grams is a lot of metal.

Tom Jones
Onex 133
AV turbo