Madjak

My lightweight crank is finally going to get a spin in an engine I'm building. So I figured I'd make up a small contraption to see how balanced it is.

I had some smallish ball bearings from another project that I mounted up to two angles clamped to the bench. The crank main bearing surfaces run on these bearings and I can spin the crank by hand to find the heavy side.



Once I find the heavy side I can add some plasticine to the light side and balance it out. I think this works down to around 5 grams or so. After that I can't really find the heavy side. I spin the crank and mark where the top rests with a marker and repeat 20 or so times in both directions. The scattering of points tends to sit on one side of the crank so I can guess at where to take off weight.

Given I can actually use this setup to find the heavy side of a stock crank (just) I think I'm in the ballpark... that or the stock crank isn't balanced very well.

I'll flapper off the weight and get it as close as I can before sending it to the machine shop to test. I'll see what they say about how good my balancing is.



Its also quite fun to spin the crank up with the drill. I had this thing humming along at 2000+ rpm on the bench. I hate to think what 9000rpm looks like.

Also, I tapped and plugged the bearing journal guide holes. I do this on all my cranks so that I can get in there and clean out the oil passages whenever I pull down my engine.

borka

iTrader: (1)

Why is there a ***** engraved into your crank? a joke at the Mazda factory?

Madjak

The forging guy at the Mazda factory has been waiting for this day for over 25 years. Someone finally appreciates his lifes work, secretly embedding phallic symbols hidden deep within crankshalf dies. His dreams of winning the internet are finally starting to come true.

Mudflap

I think you already know you'll get a ration of **** from folks around here. I applaud your attempts at balancing but this is not it. Balancing, just like on a tire, can only be accomplished at speed. Static balancing does not help when your spinning at 7000 rpm. I'm curious to see how far off you are when you get the machine shop to dynamically balance it.

Madjak

I'm mostly doing this for my own curiosity as well as to get it closer for the machine shop. It will be hard to remove weight from this crank because some of the counterweights are knife edged and can't be drilled.

When I put the plasticine on the crank I try the same weight on different ends. When I spin it fast I can feel the vibrations are different at each support depending on the location of the added weight. So I figure I'll remove the weight from end that gives the least amount of vibration.

I'll see what the machine shop says once I've tried to balance it. My guess is I'll get fairly close but not good enough for a race engine.