Rod balancing

[cbodybob]

Or weight matching
Weighing the small end to see how much can be removed there. If you look close you can see where I already had ground in the seam on the beam. I gained 2 grams there. Not much. Certainly not as much as I was hoping.
LY rods. Working with what I have

 

[Woodruff Carbs]

 

[zyzzyx]

If you need more, take it off the bottom of the cap.

 

[Nate S]

If you need more, take it off the bottom of the cap.

Agreed. Not in between. Grinding in there makes stress concentration areas. Even forging seams have strength.

 

[PurpleBeeper]

I've never done this. I always "thought" you took the weight off the bottom of the cap and/or the flat spot on the small end as needed. I remember people "polishing rods", so I just assumed removing the numbers on the sides of the rods would be fine. I would have guessed that forging seems would be OK to remove too, but like I said.....I've never done it.

 

[zyzzyx]

If you want to trim and polish the flashings off of the rods, that's O.K., but that's now your starting point
the pads on both ends are for balancing.

 

[HawkRod]

Or weight matching
Weighing the small end to see how much can be removed there. If you look close you can see where I already had ground in the seam on the beam. I gained 2 grams there. Not much. Certainly not as much as I was hoping.
LY rods. Working with what I have
View attachment 1245230

Agree with others you should grind off weight off the top and the bottom of the rods. Start with your lightest rod as your goal.

When you are done, the overall weight of each rod should be the same, as well as the weight of each end of each rod.

Note that grinding weight off of either end changes the weight of the other. So you need to sneak up on it! Just work slowly and you'll get it!

 

[cbodybob]

This is why I didn’t remove weight from the cap pad. I dimpled the pistons to get them all the same. I thought I had a pic but can’t find it. I’ll get one tomorrow

 

[cbodybob]

If you want to trim and polish the flashings off of the rods, that's O.K., but that's now your starting point
the pads on both ends are for balancing.

If I were using a better piston I would have polished the rods. I’m not a fan of oil captivity theory.

 

[70bigblockdodge]

Personally with a LY rod I would take that almost that whole lump off the top, leaving just enough to bring them close together weight wise. Weakest part of the rod is the step for the head of the bolts, which you can't fix so getting rid of as much weight as possible is better. Those pistons should be really close (better than years ago) and it is a lot of work to get much weight out of them with those giant pins.

 

[cbodybob]

Personally with a LY rod I would take that almost that whole lump off the top, leaving just enough to bring them close together weight wise. Weakest part of the rod is the step for the head of the bolts, which you can't fix so getting rid of as much weight as possible is better. Those pistons should be really close (better than years ago) and it is a lot of work to get much weight out of them with those giant pins.

Yep there was 4 grams. Pretty darn good. The rods were a different story.

 

[HawkRod]

This is why I didn’t remove weight from the cap pad. I dimpled the pistons to get them all the same. I thought I had a pic but can’t find it. I’ll get one tomorrow View attachment 1245410View attachment 1245411

Sorry for the potentially dumb question, but I'm not sure I understand.

For all the engines I have balanced (so far only 4, so I will not profess to be an expert), I make all the rods the same weight (both on the big end and the small end). Separately, I make all the pistons the same weight. Of course, pins and clips need to be the same weight too, but they almost always are identical in weight.

So I'm not sure I understand your statement that you dimpled the pistons, and that is why you didn't remove weight from the cap end. I'd appreciate if you can elaborate on what you did so I can understand better.

Thanks

 

[dvw]

Balance the big end of the rod first. The big end weight can affect the small end weight a small amount. I wouldn't ever remove weight from the beam to balance. I don't understand what "piston dimpling" is? Or what it has to do with removing weight from the weight pads.
Doug

 

[cbodybob]

Sorry for the potentially dumb question, but I'm not sure I understand.

For all the engines I have balanced (so far only 4, so I will not profess to be an expert), I make all the rods the same weight (both on the big end and the small end). Separately, I make all the pistons the same weight. Of course, pins and clips need to be the same weight too, but they almost always are identical in weight.

So I'm not sure I understand your statement that you dimpled the pistons, and that is why you didn't remove weight from the cap end. I'd appreciate if you can elaborate on what you did so I can understand better.

Thanks

The pistons were seperate. Not part of the equation at this point. There weight is why I didn’t remove weight from the cap end. Big heavy slug & only had one rod that was way out of wack. 4 were close so I wanted to keep weight on the opposite end of the piston as a measure of counter balance. So that resulted in all rods had the same cap end weight & as assembled they are damn close on the piston end. The assemblies are within 4 grams with no weight removed on the cap end.

 

[cbodybob]

Balance the big end of the rod first. The big end weight can affect the small end weight a small amount. I wouldn't ever remove weight from the beam to balance. I don't understand what "piston dimpling" is? Or what it has to do with removing weight from the weight pads.
Doug

Just drilling holes in the backside of the piston. That’s all. Dimpled them.

 

[dvw]

The pistons were seperate. Not part of the equation at this point. There weight is why I didn’t remove weight from the cap end. Big heavy slug & only had one rod that was way out of wack. 4 were close so I wanted to keep weight on the opposite end of the piston as a measure of counter balance. So that resulted in all rods had the same cap end weight & as assembled they are damn close on the piston end. The assemblies are within 4 grams with no weight removed on the cap end.

There is no sense keeping heavy bottom rod weight. You have reciprocating and rotating weight that is used in the bobweight equation. Removing big end weight does nothing to reciprocating weight. I'd read up on engine balancing.
Maybe this will help you.

Doug

 

[70bigblockdodge]

My 2235s were only less than 2 grams apart. Moving pins around got me closer.
I only had one rod (not LYs) at not quite a gram heavy, put it with lightest slug.
Keep moving Bob spring is coming.

 

[cbodybob]

My 2235s were only less than 2 grams apart. Moving pins around got me closer.
I only had one rod (not LYs) at not quite a gram heavy, put it with lightest slug.
Keep moving Bob spring is coming.

Yep I am. As you know lots going on. Hope to pick up the trans this weekend. As usual I’m behind LOL. They’re already racing here.

 

[RJRENTON]

Curiosity question.....should the rod be balanced with the bearings in place (as reciprocating weight)? Likewise, should the piston be balanced with the rings installed and if using full floating wrist pins, the pin and the pin retainers included? Just asking.....
BOB RENTON

 

[bm02tj]

Pin weight varies bearings and rings not so much but they are used in bob weight calculation