weighing pistons

[bikesandcars]

I finally noticed that the fiat pistons are marked with a number on the inside, that seems to correlate to their weight.

I'm putting an engine together and the weights for my pistons are:

406.7, 409.5, 412.7, 409.7.

I can't for the life of me figure out how to get 6 grams of weight out of a piston. Should I source a lighter piston?

Where should I take weight from?

 

[JimD]

just the piston?

Reading thru some old threads I saw one where Tony suggests weighing the rods to look for variations and then match the heaviest rod with the lightest piston, etc. I am still searching, but I thought i would throw that out and see if it makes any sense. I really know nothing about this issue myself!

http://www.network54.com/Forum/12159/message/1185432599

Update: In the end the person with the issue realized the light piston was missing a top ring.

http://www.network54.com/Forum/12159/message/1185943078/

 

[bikesandcars]

I weighed the rods, and some were a little heavier than others, the funny part was that some were top heavy, and some were bottom heavy. I'd rather have a slightly unbalanced engine than a broken rod though, so I left them alone....maybe next year I'll have more time/courage.

I brought the pistons to the same weight. (Thanks Bernice). I used a 3/8" die-grinder Aluminum Burr in my drill press and "milled" the tops of the boss's down to get the weight close (within .1 gram). I was VERY careful not to damage the pistons, doing things by hand this way is risky and somewhat dangerous, but it was more scientific (take a pass, weigh, take another pass).

for future reference, If anyone has a suggestion for removing weight from the connecting rods I'd love to know. you don't want to grind it on a wheel do you?

 

[TonyK]

Rod lightening.

I have done it on a build from years ago. 1500 Rods only, not 1300 rods.

Done by hand with a die grinding burr in a pensil grinder. Remove from the inside of the web. Take off all the rough stuff first and I also removed the square boss on the top of the rod, small end. The engine had 11.5:1 pistons and a 35-75 camshaft. Still have the engine in peices in a crate in the basement.

 

[jrt]

Instructional videos

Here is a video I came across on You Tube related to the subject. I hope the links work. If not, do a search on Costa Mesa Fiat and your subject. hope this helps. I have no direct experience with Costa Mesa, but this video and the others I viewed seemed pretty non commercial.

Con rod lightening
[ame="http://www.youtube.com/watch?v=QLpiF0E0EJU"]YouTube - Connecting Rod Balancing[/ame]