Technical Con Rod substitution.

I'm starting to get a plan together for a modified banger of English origin - from the 20's.

One of the issues with them are the aluminum con rods, they have a history of failure.

The Rods measure 10.25" c/ & 1 7/8" big end

So it brings me to my question, either does anybody know of a Rod that is similar in dimension's or is there a resource which lists various Con Rod dimensions??

I have done some looking & will continue to do so,
I can get Rods made, but they are about 3k for a set & for no more than 100hp it seems a little crazy, so I am hoping to find something which might work. Any ideas??

 

Longest rod I can think of off the top of my head would be a Willys. The rods are over 9 inches center to center. Don't recall the exact figure.

 

Thanks, what era Willy's?

 

The Willys jeeps 134. Not too hard to find

 

What fails on them ? Probably easier to modify what you have and work on fixing whats causing the failure. Maybe better oil/oiling?

 

There can't be too many options on rods that long with journals that small. Good luck with your search.

 

Get them crack tested. If they pass they are probably good for another 100 years.

 

I agree that having them checked for cracks and just running them is probably the best plan.

Quality steel alloy billets alone are quite spendy.

$3K for a set of finished custom-made connecting rods is not out-of-line, even if it is just 4.

Engineering, CAD, FEA all need to be done. That is a portion of the cost, and a portion that cannot be amortized over multiple sales.

 

If they have a history of failure there's probably a typical failure point. For instance, the sharp cut where the bolt heads seat or maybe the small end. If you can determine what that point is you might be able to have them reinforced before reconditioning.

 

Agree, find the best heliarc guy in the county, box both sides with plate, weld up the area cut for bolt heads and convert to ARP cap screws. Have the rods reconned on a Sunnen rod shop.

jack vines

 

To cement this, just the material to make these, assuming 4340, would be $1,100.

What @PackardV8 says is sound advice.

 

@gimpyshotrods The new Rods I speak of are a very high quality forged Rod & I can see that they are worth the money, it just seems for 100hp or less it's over kill.
I'm not sure where they fail, but suspect you are right @TCTND
@PackardV8 that's certainly an interesting idea, I have a guy I can chat to about this,

I have assembled engines, but haven't 'built' engines, so I don't know fully what can be done.

These engines have a full pressure bottom end, but only 3 mains.

Most people building these engines replace the rods, I just don't know if this is based on myth or reality. I could get a hardness test done to see what they are like....

 

With what? Perhaps you could just replace yours with the same ones most people use.

 

I have made steel rods to replace the aluminum rods on a Norton motorcycle and managed to get them 100gr lighter - so it is doable to replace those rods with something far stronger. Never weld an aluminum drop forged rod - it will lose a lot of strength and fail.

 

The $3000 custom made rods.
I may have to go this way, I have time & I was hoping to find an OEM steel rods that might be close....

 

Thanks, my machining skills are not up to making rods, but will keep pushing forward

 

Generally Alum rods break do to lack of oil and they are trying to stick to the crank pin, I am thinking no insert bearing? If no bearing then oil pressure/volume is your friend, get the pressure/volume up and run them. A home shop machinist [me] could make them from 7075 Alum plate with adjustment in bolt area for strength or cap screws like suggested above. They don't have to be that shapely do they?

 

They are Babbit/white metal bearings,I think part of the concern is fatigue on the Ally (duralumin) rods.
They tend to machine a bronze shell & then pour the Babbit into them, to reduce the thickness of the poured metal.

 

I tractor pulled with a 18hp Tecumseh engine and the stock forged [alcoa] rod was plated with babbit maybe .001 thick and held up fine with just splash lubrication moded to about 45hp @ 6500. Guys with Kohler engines were boring the cast alum rods out to take an over the counter insert bearing [1.5 id] and still slash lube and virtually eliminated breakage. Is the crank pin at 1.875?

 

ask Argo in Sydney down here ( https://argorace.com.au/) they will make you a set and it could be cheaper given the value of the Oz Banana to the GBP

 

The only rods that I can think of that would even approach that length would be straight 8 Buick.

 

I am down here too, Argo are the one's who make them. If there was a job lot 5/6 sets they will be a bit cheaper. Thx

 

Thanks, I will chase it up. I figure there should be something, old truck, tractor something.

 

Find the donor rod ends you want, graft em together, and run the hell out of em! They did it back in the day, and it works great for a relatively low power engine. Here are some pics of a set of A big end T small end rods cut to length and boxed to fit in a T with A crank

 

9.1" ish

 

They are in the 8" range.

 

This might be the answer @Kevin Pharis, just have to find the right size rods & someone who is brave enough to weld them up! a question, it looks like you removed the web before welding them up? I guess removing stress raisers is the key with the removed material? Have you photo's of the finished item?

 

In the antique tractor pull world, John Deere 2 popper guys used to shorten their rods like that when massively stroking cranks. How much RPM do these engines spin?

 

Out of interest, what engine are you intending to use?

 

Have you looked at motorcycle, tractor or aircraft?