Balancing Connecting Rods

[Steve Bryant]

I have a question for the experienced engine builders:

When balancing connecting rods, where is the best place to remove material from on the big end and the wrist pin end to lighten them to match the weight of the lightest rod ? You can appreciate that I don't wish to weaken them in any way.


Thanks,
Stephen

[Colin Reed]

HI Steve,
What type of rod, Standard  Clamp bolt  fully floating After market ?
Also min and max weight for both Ends

Cheers
Colin
NZ

[Stuart Giles]

The forging "dimples" on the big ends you can see just above the big end cap in the photo below are a place you can remove weight without weakening the rod in any way; reducing/removing these also allows you pass the big end down the bore when building up your motor with the block already bolted down. If you can't get enough reduction from the dimples, reducing the size of the flange on the big end cap slightly is worth a gram or two.



once you have equalised the big end weights, there shouldn't be too much to remove from the small end as there is relatively small weight there anyway. Start equalising here by grinding away any forging flash at the small end; you can see this  in this photo where I'm balancing a set of non A7 rods.

[Speedex750]

Hi Steve,
There's quite a bit of material around the big ends but not much at the little ends. Depending how close they are I would suggest you balance to the second lightest rod and try to add to the lightest by trying different gudgeon pins - there is variance of a few grams amongst different batches depending on how big the hole is made. Fine adjustments come from a washer under the big end nuts and varying the clamp bolt length. It is possible to get within a few grams on this but you need lots of patience and keep rechecking your measurements for consistency.

Hope of use, Dave

[Chris KC]

Also any place where a previous owner has made between one and four hacksaw cuts to indicate rod number (wince). Smoothing these out will remove the stress raiser; though you might do better to find another set of rods.

[Steve Bryant]

HI Steve,
What type of rod, Standard  Clamp bolt  fully floating After market ?
Also min and max weight for both Ends

Cheers
Colin
NZ

Colin the rods are the stock standard rods that came with the engine (1929) metaled big ends with clamp bolts on wrist pin ends and regular clamp bolts with nuts and split pins.


  Connecting rod.jpg (Size: 103.81 KB / Downloads: 251)

[Hugh Barnes]

Steve - apologies if I sound like trying to teach my Grandmother to suck eggs, but have you crack tested the slots at the little ends? A known point of failure and absolutely needs to be checked if you have not yet done so...

hth!

[Robert Leigh]

Steve - apologies if I sound like trying to teach my Grandmother to suck eggs, but have you crack tested the slots at the little ends? A known point of failure and absolutely needs to be checked if you have not yet done so...

hth!

This can be done by cleaning the rod thoroughly in paraffin and drying it off with clean rag or paper towel; then do up the little end bolt tight. If there is a crack, paraffin will be squeezed out from it. Professional crack testing may be thought better, but my method is quite good and costs next to nothing. It can save getting cracked rods tested expensively.
Robert Leigh

[Colin Reed]

HI STEVE,
If these are for a standard or mild performance upgrade, I would just check for cracks also the condition of thread for clamp bolt,
lightly grind out any forging marks ie a long length of rod and on the cap.
Replace the cap bolts and use (HT) Nylocs. Reason they will have stretched and the Nylocs because they can be TORQUED to the set ftlbs 
and left were as castellated nuts might have to be over tightend to line up with hole in bolt.
Lastly if the rods are Relatively close in weight I would not bother to get them spot on

Hope that Helps
Colin
NZ

[Steve Bryant]

HI STEVE,
If these are for a standard or mild performance upgrade, I would just check for cracks also the condition of thread for clamp bolt,
lightly grind out any forging marks ie a long length of rod and on the cap.
Replace the cap bolts and use (HT) Nylocs. Reason they will have stretched and the Nylocs because they can be TORQUED to the set ftlbs 
and left were as castellated nuts might have to be over tightend to line up with hole in bolt.
Lastly if the rods are Relatively close in weight I would not bother to get them spot on

Hope that Helps
Colin
NZ

Hi Colin,
these rods are for a absolutely stock unmodified engine. I'm having the engine dynamically balanced to make it run as smoothly and vibration free as possible. Rods have been crack tested and threads  are ok.  New cap bolts with nylocs will be fitted for all the known reasons. Thank you for the suggestions.

Stephen