1940 221 rods
 

Crazy little thing, she had ..
1 - L1 rod
2 - L2 rods
2 - L3 rods
And 3 with no numbers on them .
Probably ran like a top …

Re: 1940 221 rods
 

Some large overhaul shops didn't pay any attention to the numbers on the rods. They didn't keep track of matched sets.

Re: 1940 221 rods
 

rotorwrench, that kinda sucks hu, Im kinda weird about putting things like they should be, don't think that's gonna happen here, I think Ill measure and weigh them all and if all is good, Ill just have everything balanced.

Re: 1940 221 rods
 

Don't get too suprised by the outcome .

Re: 1940 221 rods
 

Why is that Ggmac ?
I bet it would run fine right there lol ..

Re: 1940 221 rods
 

Always a good idea to check each rod anyway, so not much, if any, extra effort.

Re: 1940 221 rods
 

You can pretty much look at the forgings and numbers/letters to determine if they are the same 'version'. Unless they threw in some earlier rods (really spindly), then they should all be either 91A or 21A rods (all 8 of them). If you are having the rods balanced, make sure the shop knows the specifics of how you balance flathead rods - it is NOT the same as modern rods that have 'balance pads' on them. Grinding on the bottom of the big-end caps is NOT the correct way to do it - should be done in a lathe with a special fixture.


Here is an example on my lathe - using 21A rods and my own fixture:

Attachment 388987

Attachment 388986

Attachment 388985

Here is the 'wrong way' - that I see all too often (great way to weaken the cap):


Attachment 388988

Re: 1940 221 rods
 

Thanks Bored&Stroked, where should the weight come off ?

Re: 1940 221 rods
 

You'll notice on the second picture where there is a fresh machined area around the perimeter of the cap. If you look at original rods, you'll see that Ford did it the same way. They also took material off the small end of the rod by turning the bushing area on both sides. Just take a bit of time checking out an original rod and you can see exactly what I'm talking about.

Re: 1940 221 rods
 

What I meant is , if you're having it balanced , let them do it . I wouldn't add any info to the mix .
It's not just the overall weight . If you know this please forgive. Its measuring the big end and little . With the nuts your going to use . Not that a buggered nut would throw off the numbers too much .

Re: 1940 221 rods
 

I use an assortment of ARP nuts to also help adjust the big end weight.
Lawrie

Re: 1940 221 rods
 

Be a bit careful about aftermarket nuts on the early 91A/21A/29A rods - in some cases the base dimensions don't actually fit the machined areas of the caps (they ride on the perimeter).

So put some die-chem on the rod caps and tighten down the cap (in a rod vise) with the new nuts. See where the contact pattern is. You may find that it is NOT in the machined area/base, but out on the machined radius toward the inside. If so, this is a problem.

Re: 1940 221 rods
 

You might be able to measure things like the bore diameters, but you will not be able to determine if they are balanced by overall weight. There are specific tools/methods used to weigh the big-end, versus small end --- and you can't just throw a rod on a gram scale. So, unless you have the tools and knowledge, don't think you can figure out your rod balance at home. :)