TECH...440 Rods in a 392 Hemi

[Bugman]

There aren't many choices when it comes to connecting rod for your 392. Bearings also aren't the cheapest. 392 parts are getting very expensive. If only there were a cheaper alternative.

But wait...There is. Chrysler used the same diameter rod bearing in their RB motors. That means that RB rods can be made to work in a 392. 440 rods specifically. Common, strong, and way cheaper than Hemi stuff. With some minor modifications, they work great. Join us as we briefly show how to convert 440 rods to Hemi's.

Bugman Jeff

[Bugman]

The problem. I don't trust the used aluminum rods in my motor, and stock 392 rods won't handle the abuse I'm going to give them.

[Bugman]

The solution. Stock 440 Mopar rods. A big thanks to four-thirteen for donating a pair of rods to practice with.

[Bugman]

Now comes the tricky part. 440 rods are exactly .200" shorter than a stock 392 rod. You can see the difference here.

[Bugman]

More importantly, 440 rods are approximatly .020" wider on the big end. Here you can see the gap above the aluminum rod.

[Bugman]

Using a vernier height gauge, you can see the difference better, and get a very accurate measurment. My rods were .028" wider than the stock 392's. .028" isn't very much, but in an engine, it makes all the difference in the world.

[Bugman]

What's the best way to remove .028 from a connecting rod you ask? With a surface grinder. All good machine shops should have one. I was able to use the one at the school where my Dad used to work. If you're not familier with a surface grinder, it's a very percision grinder that uses a magnetic vise. It is made to grind things perfectally flat. The wheel moves up and down, and the table moves left and right, and in and out. This particulat grinder is accurate down to .0001"(one ten thousandth). Make a pass or too, take the rods off and try them. You DON'T want to take to much off. Grind the same amount off of each side of the rod. You might have to re-chamfer the side of the rod that goes against the crank web.

[Bugman]

Keep trial fitting the rods until you get them to work. The Chrysler spec for rod side clearance is .006 to .014. That gives you a little fudge factor. You also have to narrow the bearings. This is easily acomplished with a dermel, or small file.

There you have it, 440 rods on a 392 crank. I'll post more when I get to fitting the pistons. You have to make up for the missing .200" on the 440 rods.

Bugman Jeff

[Gr8ballsofir]

cool. I've got 2 questions:

1. You wrote "440 rods are exactly .200" shorter than a stock 392 rod."

This will affect your compression right? Good or bad?

2. will these work in the earlier 354's & 331's? Desotos?

Thanks,
Mark

[Bugman]

1. .200 will drastically lower your compression. Generally, custom pistons will be needed. But if you are building a high performance moror anyway, you'll probably be buying non stock pistons. In my case, I'm using a stroker crank. A longer stroke with a shorter rod will balance eash other out...almost. I have 3 sets of pistons that I am going to try and make work. I'll keep you posted.

2. Tall deck Dodge and Desoto's, and 331/354 motors have smaller rod journal diameters and shorter rods than the 392. I've heard that 400 Pontiac rods will work in these motors, but I have never tried it.

-Bugman Jeff

[Bugman]

Also, I forgot to mention...The 440 rod has a 1.090 wrist pin where the 392 is .9843". If you need custom pistons, you can have them made with that pin, or you can have your machine shop resize the 440 rod.

-Bugman Jeff

[Shaggy]

WOW!!

Good article anyone know about the pontiac rods in a 331????

[LUKESTER]

Almost all aftermarket 440 mopar rods are available with .990 wrist pin holes........... Most mopar racers desire the .990 pins (chevy) over the larger stock size..... LUKESTER

[studeboy]

Darn it 51 F-3 you beat me to my big suprise. The Pontiac 400 and 455 rods are the EXACT same length as the Chrysler 331-354 rods. If I remember correctly the big end is also the same but the wrist pin is .004 smaller on the Pontiac. That could be taken out of the rod or the bushing as they are full floating. Have also been told that Chevy smallblock pistons can be used but not sure on that one. (Wrist pin location is different on each CID motor) Eric

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49 Studebaker P/U

[Mel]

good info! bttt!

[four-thirteen]

TECH...440 Rods in a 392 Hemi
or
TECH...440 Rods in a motor made of wood http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif
looks like everything is working out ok...

[Evilfordcoupe™]

Hey Bugman,

What are you building that you need that much insurance??

-Jason

[Mel]

If you know Bugman, it's never what he's building, but how he plans to drive it that counts.... he needs all the extra insurance he can get. http://www.jalopyjournal.com/ubbthreads/images/graemlins/blush.gif

[FWilliams]

2 questions

1] how are you going to duplicate the chamfer for the crank fillet

2] what are you going to do with the aluminum rods? http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[Bugman]

413-
The wood is actually a vintage stud girdle. The guy I got it from said it helped absorb crankshaft vibrations in a Fuel motor http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

Evil-
Pulling tractor race motor + '55 Plymouth = Fun.
I'm going to go Honda hunting.

Racefab-
The chamfer can be reproduced with a 1/2 round file and some time. A dremel works too, but it can work to fast sometimes so you have to be careful. I noticed that the stock chamfer wasn't machined overly percise on the 440 rods. Taking only.010 off that side didn't change the dimension that much, and I still had enough clearance.

2. I dunno what I'm doing with my old rods yet. I have 1 complete M/T set, 1 set minus 2 rods, and 1 mismatched set of Howards. I'll probably save them for my spare block and crank. I don't know how many runs they have on them, and I don't trust them.

-Bugman Jeff