Connecting rod lengths and weights

[Rafedial1]

This mission is in it's infancy. But I will still share what I have gathered so far.

Questions: how important and difficult is it to have a perfectly balanced rotating assembly?

How hard is it to find a set of (8) rods that are exact same dimensions?

Any year range/miltary 6.5 that had stronger con rods? (prob not)

Is it best to weight the rods separate, then pistons and then combined weight to achieve a medium or average that all can be on, or slightly above/below the medium?

Has anyone found better fasteners/hardware for the con-rod bolts/nuts? like aRP stuff?

What does shot peened rods mean exactly and what does it do?

To do: weigh all of my spare connecting rods that are in good condition
measure lengths(gonna have to upgrade my PMI tool set)

 

[ak diesel driver]

I'm not sure how they go about shot peening but it's to relieve stresses

 

[3500GMC]

To the best of my knowledge...

This mission is in it's infancy. But I will still share what I have gathered so far.

Questions: how important and difficult is it to have a perfectly balanced rotating assembly?
Essential for high RPM use. Special tools in the machine shop
How hard is it to find a set of (8) rods that are exact same dimensions?
When resizing rod's big end, it can be done then.
Any year range/miltary 6.5 that had stronger con rods? (prob not)
All are forged, all are the same.
Is it best to weight the rods separate, then pistons and then combined weight to achieve a medium or average that all can be on, or slightly above/below the medium?
All reciprocating assembly components are weighed separately. Big and small ends of rods are balanced to each other, all small the same, all big the same. Pistons are weighed and made all the same weights. One COMPLETE rod, rod bearing, piston, pin, rings, clips and a known weight for the quantity of OIL that clings to that assembly is factored into calculating 'bob weight' for balancing the crank. The crank is spun with the bob weights, which actually represent the piston & rod assemblies. Material is added or subtracted from the crank throws accordingly.
Has anyone found better fasteners/hardware for the con-rod bolts/nuts? like aRP stuff?
Not yet. GM is all that's readily available.
What does shot peened rods mean exactly and what does it do?
Eliminates stress risers on the surface of the rod. Said to make a rod stronger.

To do: weigh all of my spare connecting rods that are in good condition
measure lengths(gonna have to upgrade my PMI tool set)

 

[chessie 6.5]

Just my opinion of course, but since these engines only run to 3500 rpm, the stock rods and bolts should be plenty stout.Maybe install new oem bolts during build. Also balance imperfections won't be near as noticeable. If you plan 5000 plus rpms, contact Heath and see what he did for the salt flat engine.

 

[3500GMC]

IIRC Heath is using GM bolts and no special rod prep (purportedly) and turning 5500. Who only knows what else.

 

[Rafedial1]

Good ole Heath. His name is iconic in the 6.5 market. I marvel at the path he has created for the 6.5 and it's performance. However I too am on my own path, and I will respectfully decline his advice/guidelines on building this engine.

 

[Rafedial1]

To the best of my knowledge...

great info 3500GMC. thank you.

 

[WarWagon]

Heath is using a 6.2 bottom end with the thicker pistons the 6.2 has. Other than that you may just be reinventing the wheel. The GEP is the best improvement by far if you can get it.

 

[6.2 turbo]

You build yours with low compression and I will build mine higher than stock . Then we should somehow compare the two. There is starting to be dynos showing up at local car shows,so maybe I will dyno it . Seems a long way off though .

 

[bobbiemartin]

Questions: how important and difficult is it to have a perfectly balanced rotating assembly?

How important? Depends on what you are after. If you want the smoothest possible engine, then yes its important. How difficult? Without specialized equipment you can't do it. So its basically taking everything to the machine shop and paying them to do it.

Is it best to weight the rods separate, then pistons and then combined weight to achieve a medium or average that all can be on, or slightly above/below the medium?

Weighing a rod with a conventional scale is basically worthless. You have to weigh each end and you need a special scale to do this. You get all the big ends the same and all the small ends the same and what follows is all the rods weigh the same. The pistons can be done on a scale. What is basically done is the remaining 7 pistons are brought down to the lightest one.

Has anyone found better fasteners/hardware for the con-rod bolts/nuts? like ARP stuff?

I don't know if ARP makes a rod bolt, but the factory ones are probably more than adequate. You just don't hear of these engines having rod problems. Blocks are another story!

What does shot peened rods mean exactly and what does it do?

Shot peening is a surface treatment, sometimes done on rods. Here is a pretty good article on shot peening

To do: weigh all of my spare connecting rods that are in good condition
measure lengths(gonna have to upgrade my PMI tool set)

Again as I said, you are wasting your time weighing the rods. And a good machine shop can check the end to end length for a few dollars far better than you probably can.

How hard is it to find a set of (8) rods that are exact same dimensions?

Rods can be resized slightly if necessary. The shop said mine were all within spec.

Any year range/miltary 6.5 that had stronger con rods? (prob not)

Not that I'm aware of.



I had my 6.5 I recently rebuilt balanced. One piston was out a bit, the rest were pretty close. The balancer had to add two pieces of Mallory (or heavy) metal into the crank counterweights to get it balanced. You have to take everything, the crank, rods, pistons, front damper and flywheel/flex plate. You also need one set of rings and a rod bearing. Did it help? I think so, but its really hard to say. Its seems smoother, but maybe its just me hoping. If you have the time and money, its probably not a bad deal. If not, I probably wouldn't worry about it.

Here is an article on balancing you might want to read.

 

[ak diesel driver]

I balanced a 6.2 once. it ran really smooth. Even the guy I built it for commented on it.