Is it Possible to ID a rod's weight group from the markings?
 

For example, I have a rod with the following markings on it. Does any of this suggest what the weight group is for the rod? Note that I suspect that my rods are the original rods and have not be swapped prior to my tear-down.

Cast on the rod: 911.103.105.OR
On the bottom of the rod is stamped "311" or possibly "811" on both the rod and the cap,
There are also numbers cast at the bottom of the rod and cap: 20, 924 and 1130

AFAIK only rods installed as replacement are so coded. The final digits of the part # stamped on the con rod shank will indicate the weight group.

for instance
911.103.015.31 was weight group 1 645 - 654g rod code 31
911.103.015.32 was weight group 2 654 - 663g rod code 32

Other wise if they are originals, weigh the complete rod w/o bearing shells, max permissible deviation was 9 g. on the '76- '77 2.7 & 3.0 other engines had similar but unique codes all 9g max deviation

Bill,

So both my rods and John's are replacement rods (part numbers end in OR).

This # 'stamped' on the conrod shank that you describe, is it the one stamped on both the rod and the cap? Because all mine are different. All my other numbers are cast into the rod and surely they don't determine the weight prior to casting?

Thanks
Tristan

When your engine is balanced and the rods reconditioned, a standard procedure is to bring them all to the same weight and balance them end-to-end. The weight group markings and replacements are mainly for replacements where the rods are not being taken out of the engine and reconditioned (rare case). See the factory manual / spec books for more information on this...

-Wayne

Wayne,

Well that's exactly what I'm trying to find out. Here's my case:

I'm looking for a replacement rod for my rebuild. The rod it will replace weighed 660g. I'm trying to buy another one from John who posted this thread. We don't know whether his rod is in the same weight group and your book doesn't say how to identify the weigth groups. Of course, I could have not read that bit, but I think I've read the book cover-to-cover a few times.

My rods are going to be reconditioned because I'm getting new small end bearings and wrist pins.

Thanks for your help in advance.

Tristan

According to the shop manuals only replacement rods are coded. If the rod(s) in question were oem then the part # is not a reliable indicator of weight. If ordering from a dealer it is.

Just weigh them. All you need to know is the weight of the lightest and heaviest and be sure that the replacements don't make the spread greater than 9g.

Tristan;
Since you are going to recondition the entire set of rods anyhow, the weight group really doesn't matter since the rods' weights will be changed as part of the reconditioning process. As Wayne described, adjusting the rod weights is part of the reconditioning process -- at least if you specify it to your machine shop.

Agreed- the machine shop will take the weight down to the lightest rod, within a few grams. Tim just got a set done; they are all balanced nearly perfectly. 5 rods at like 668 and one at 669. Pretty much SOP for the shop, I wouldn't worry about it.

While I agree with this, my machinist says that there isn't really much room to remove material and thus you might not be able to match them.

??

John,
Let me know if you need to borrow my scale.
-Chris