Toyota Celica Supra Forum banner

181 - 185 of 185 Posts

·
Premium Member
Joined
·
4,055 Posts
Some good reads in there. A few that I've seen before but that Hot Rod page in particular was a new one. Pretty much reinforces my thought that the crank and lower rotating parts need to see a machinist. No way in hell could I afford a balancing machine. I could probably build a gravity balancer out of some old flexplates and bearings with a steel frame, but that seems a little excessive for the moment when a machinist will typically do the job much more accurately with a digital balancer for $50 or better. Maybe an interesting endeavor for the future, though 🤷‍♂️

An entire gram still seems like a large deviation for the effort, imho. There are manufacturers that sell sets within that threshold. It shouldn't take much longer to get down into at least the tenth range.

I was looking at one of my old pistons today and did notice how much material there is around the wrist pin holes that could likely be removed safely. I've also read that the bottom of the skirts is a good area to take from if you make sure to smooth it out well while grinding.
Maybe it's a bit fuzzy after 40 years, but I could be wrong. I think I probably meant "within one gram", which would be +/-.5 gram. I haven't read the articles I linked to in a while, so I don't know what a "precision" balance would be these days. You definitely hit a point of diminishing return with this stuff, and it doesn't make any difference beyond a certain point. To do it to .001 gram, for instance, would be meaningless. I know my machine shop had State-of-the-Art Stewart-Warner gear, and was highly respected by the "pro" guys. He cost a bit more, but did superb work.

Besides, my Dad knew his Dad from the Navy, and my Dad had sold him his Bridgeport mill, Logan lathe, and Hisey-Wolf surface grinder.

As far as balancing the pistons, cast pistons are generally closer together than forged ones, but I don't remember the percentage difference. I've seen people drill holes in the pin boss area to remove metal, but "My Machinist" didn't like that because it left sharp edges that could lead to stress cracks, fatal in cast pistons, and definitely Not Good even with forged ones. That's why he milled the bosses equally to lighten them.

I saw him do a crank once, and it was very interesting to see how they detected the amount of unbalance, and it's position on the crank, so you'd know how much to drill, and where. For the amount to drill, he had a chart from S-W indicating drill bit sizes and depth of vs metal amount removed for different metals. "The Book" also had tables and charts for the bobweights used on the crank throws. Really cool stuff for geek like me to learn about.

I'm sure things have changed int the last 40 years, but the basics are still the same. As Mr. Scott would say "...Cap'n, I Kenny Violate The Laws of Physics!"
 

·
Registered
Joined
·
180 Posts
Discussion Starter #182
You clearly know a wealth more about this than I do so it will be difficult to confirm most of this. I've never set my eyes on any of the equipment you've mentioned. Some reading and several youtube videos are the only reason I have the vague idea that I do of their function and anatomy.

One thing I will say is that it seems to be almost unanimous (based solely on tech articles and forums) that both the pistons and rods land within five-hundredths of their respective lightest individual. Again, this is gathered from reading and some machinist videos, and absolutely no hands on experience.

Theoretically, it makes sense to be in the .0x threshold. Tenths should suffice, but several tech videos have shown how easy it is to narrow into that extra place, so I shrug and say "why not?". Figure it couldn't hurt.

I'd have to agree that thousandths is overkill, if even attainable.
 

·
Premium Member
Joined
·
4,055 Posts
You clearly know a wealth more about this than I do so it will be difficult to confirm most of this. I've never set my eyes on any of the equipment you've mentioned. Some reading and several youtube videos are the only reason I have the vague idea that I do of their function and anatomy.

One thing I will say is that it seems to be almost unanimous (based solely on tech articles and forums) that both the pistons and rods land within five-hundredths of their respective lightest individual. Again, this is gathered from reading and some machinist videos, and absolutely no hands on experience.

Theoretically, it makes sense to be in the .0x threshold. Tenths should suffice, but several tech videos have shown how easy it is to narrow into that extra place, so I shrug and say "why not?". Figure it couldn't hurt.

I'd have to agree that thousandths is overkill, if even attainable.
It's experience mixed with education. I'm a retired Engineer, and been doing stuff like this since high-school, over 50 years now. Back when I was doing this stuff on the side, I mostly worked with Big American Iron, but did foreign stuff, too. I suppose 40 years of technology has made improved resolution of the unbalance a snap to do, but I haven't kept pace with that type of machinery. There's some things it's well worth paying a shop to do, and if you understand what they're doing, you're ahead of the game. If they respond to your questions with things that make sense based on what you know, that's a good sign that they know what they're doing. If they can't, or blow smoke at you, find another shop!

It's good to see younger guys getting involved at this level of technical understanding. Once you learn the basics of this stuff you'll enjoy your car more. Understanding how all the little bits get together and play beautiful music is a cool thing.
 

·
Registered
Joined
·
15,059 Posts




These are just a few I grabbed for you. They are from more professional channels
 

·
Registered
Joined
·
180 Posts
Discussion Starter #185 (Edited)
HP academy is awesome and Andre explains everything thoroughly enough to make even the FNGs savvy. I think that top video was the first one I saw with someone removing material from the skirt. Looks like one could probably get the bulk of it from that one spot.

I sure wish I had the money to spend on a manufactured jig like he has. I'd be much more confident balancing the big end.
 
181 - 185 of 185 Posts
Top