21A rods set up on a 4" Merc crank
 

On oil clearance by using the 21A rods.
I has a baby stroked 4” crank done in LA back in the days, and it's Ok on them mains but
need a undercut on the rods.
I has a set of NOS 21 A rods and sets of new but old bearings.
But how to set-up clearance on this design ( full float ) I has Berco crank grinder so I do it myself.
How is one set-up diameter in the rods, and how to measure clearance with bearings like this ( never been into it before )

Then on oil, by using the full float, what oil do they like, I has a new NOS 8BA pump ( maybe wrong or not needed as to 'much' pressuare ) and a truck oil pan I will make a screen and a scraper inside.

This is not a street rod engine, but not full race.
But for streets, but minimal use ( but like rew up )

Re: 21A rods set up on a 4" Merc crank
 

https://www.fordbarn.com/forum/attac...4&d=1751042912

https://www.fordbarn.com/forum/attac...5&d=1751042912

Re: 21A rods set up on a 4" Merc crank
 

Big end of the rods should measure 2.220. Then measure the diameter of the crank journal then measure the thickness of the bearing at the crown and multiply by two. then with a little arithmetic you’ll find your oil clearance.

Re: 21A rods set up on a 4" Merc crank
 

I has a bearing thickness micrometer and I can get the std Ford tech ( AERA ) anz normally I use 0.001” clearance on diameter and in race I add 0.005” and oil 5-20 or 10/30 but in this case I has no experiance, will use custom piston and 1 or 1.2 mm rings.
This is not a cruzer, but not just ’race’.

Re: 21A rods set up on a 4" Merc crank
 

I sent you an message response . . . it should help with your questions.

One thing to note is that the bearing MUST float - easily. This requires that you "tune" the bearings to match the crank/rods. You'll want a total clearance of at least .002 . . . up to .0025. With a good oil pump, it is better to be loose than tight. As noted, you need to measure the bearing thickness in order to compute the total clearance.

I'm sure you've seen my Youtube video on the manual procedure to tune/polish the bearings so they float.

My preferred bearings for a 4 1/8 stroker are the Cadmium-Silver variations . . . usually titled "Truck and Bus" from Ford. They are a much softer material than the harder bronze ones and don't wear the rod journals as much as the more common bronze variants.

Re: 21A rods set up on a 4" Merc crank
 

Also, if you can have the rods "shot peened" . . . that is a good process to stress-relieve and add some strength. You'll need to balance BOTH ends of the rods and make sure that you do NOT grind the strengthening rib off of the rod-cap.

You need to make a fixture for your lathe to cut the side-area of the rod caps to set the big-end weight. Ford NEVER ground the rib on the bottom and these rods do not have balance pads like modern rods.

Couple pics on my setup:

Attachment 568921

Attachment 568922

Attachment 568923

Attachment 568924

Here is what most shops will do . . . they grind the bottom cap rib! They don't know any better and weaken the cap:

Attachment 568925

Video on bearing sizing:

https://www.youtube.com/watch?v=CyVLsPdbhS8

Re: 21A rods set up on a 4" Merc crank
 

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Re: 21A rods set up on a 4" Merc crank
 

Great, thanks !

I can shutpeen and I will ofcourse check the bigends, but if some grams off in this set I really don't matter.
I will go upp on the diameter 0.001" on the rods and I has a AMC grinder I can use so surface will be nice.
I target in a oil clearance at 0.0025".
Actually as it is now I can slide in a set less use any schottbrite and the rods is STD now at 2.220" but I will add up the diameter and make shore all bearings rotare fine in the rod and later on when crank pin is - 0.020" I will check so its rotate.

A question.
This old ideas by use this rods in a stroked crank will fullfloat bearings, was it in big issues or does it work RPM it, if all tech is Ok ?

Re: 21A rods set up on a 4" Merc crank
 

Hank from what I have been told by the fellows who once ran the 21A rods in the old days for their 4 1/8 stroked cranks the rods worked perfectly. My personal experience using 21A rods was also with the Merc crank stroked to 4-1/8 I was burning alcohol in my restored altered. The rods worked fine my sets were also NOS.
Bored and Stroked {Dale} has lots of experience in what I call the modern era using the 21A rods in a Hot Rod flathead Ford engine application. As he wrote above that's the way to go.
Ronnieroadster

Re: 21A rods set up on a 4" Merc crank
 

Thanks Ronnie . . . as usual, we tend to be on the same flathead page. :D

As I mentioned to Hank in a DM, it is not a bad idea to open up the big-end of the rod about .001 or so . . . to achieve a bit more oil clearance. This is probably more important with the hard copper type bearings, than with the Cad-Silver ones (where it is easier to "polish away" some bearing material with ScotchBrite).

When using a rod hone, you have to make sure that the final operation highly polishes the big-end bore . . . and it is a bearing surface. You do not want a cross-hatch like on a normal insert bearing rod.

Re: 21A rods set up on a 4" Merc crank
 

Ronnie and B&S have nailed this process to the T. I am right there with them. I too give them that extra .001 clearance and to polish bearing surface of rod I use 1600grit wet and dry sandpaper wrapped around sunnen honing stone with fluid

Re: 21A rods set up on a 4" Merc crank
 

Thanks for that Tony. Was wondering the best way to achieve a polished mirror finish on them.

Re: 21A rods set up on a 4" Merc crank
 

I has the fortune to know the guys at Verdi rods & oilpumps.
They has a grinder that create this surface, se picture.
AMC made that machine.
I make dry sump oil pump parts to them right now.
I think the extra 0.001" sounds a good idea as get all this spun nice and free.
What I'm think of if I ever need get the copper 'look' surface of the bearings, so has any ideas what it is ?

Re: 21A rods set up on a 4" Merc crank
 

They are copper-bronze bearings . . . it isn't just a "look" it is the material. They are hard and they tend to wear the crank journals more than the cadmium-silver (Heavy Duty Truck and Bus) bearings that I prefer.

Many of the bearing manufacturers (including Ford) made both the copper/bronze versions as well as the "CS" - Cadmium Silver versions. I only use the cadmium silver versions in my strokers running full-floater bearings. They are a lot harder to find than the copper/bronze versions - so I've "collected" a few sets over the years.

Example: Federal Mogul made two versions of rod bearings to fit the 21A rods:

1) CA - copper/bronze
2) CS - cadmium-silver

Part Number Example: 9800CS-30 (.030 oversize).

Attachment 569046

For modern OHV folks, the cadmium-silver versions are similar in concept to some of the Vandervell bearings we run on blown OHV engines with a lot of boost. The goal is to take a bit of shock out of the system and "play nice" with the journals.

Re: 21A rods set up on a 4" Merc crank
 

It's always something new to learn !

In my stocker 426 Hemi the guy in USA helped me with that combo did like the "soft" 'Vandervell' mains but he used Clevite race bearings on rods.
When thoose Federl Mogul boxes was empty ( soft ones ) I bought I then used Clevite on the mains ( Clevite on the rods ) and no issues or a case I noted.
But it did eat rodbearing since heavy rotating and RPM over 8.500 and very thin oil 5-20.
In my new Hemi I used Calico coated and base is Clevite and this is the hard bearings/race, but I has a Crower crank and it can't be compared here on this FH.


-So should I start get worry and look for the cadmium-silver ( 020 )

Re: 21A rods set up on a 4" Merc crank
 

https://www.fordbarn.com/forum/attac...2&d=1751221636

https://www.fordbarn.com/forum/attac...3&d=1751221636

Re: 21A rods set up on a 4" Merc crank
 

Re: 21A rods set up on a 4" Merc crank
 

Is the clearance on floating rod bearings measured on each side of the bearing shell, or is the clearance split between each side of the bearing shell?
Asked a different way, is the clearance the total for both oil films, or is the clearance for each oil film?

Re: 21A rods set up on a 4" Merc crank
 

Quoting Bored and Stroked from post #5
"You'll want a total clearance of at least .002 . . . up to .0025"