Author Topic: How to build your own racing connecting rods? (Read 5234 times)

Hemi Joel · « **on:** June 08, 2021, 02:33:13 PM »

Hi, I'm going to need custom steel racing connecting rods with a length in the 9-in range. This is for the blown 337 Lincoln flathead for land speed racing. I got a price from Carrillo of about $800 per rod.
So I want to investigate the feasibility of making a couple sets on my own. Has anyone done this? If so, what is the material and the process?
It only has a three and a half inch bore, so I don't think the big end of an aluminum rod would fit through it, plus with a track length of 5 mi, I have heard that aluminum rods aren't the best for land speed racing. That is why I'm planning on using steel.

Thanks, Joel

chilly460 · « **Reply #1 on:** June 08, 2021, 02:58:29 PM »

Might take awhile...

frnkeore · « **Reply #2 on:** June 08, 2021, 04:18:54 PM »

Do you have a good milling machine and a good machinist available?

Hemi Joel · « **Reply #3 on:** June 08, 2021, 04:41:37 PM »

Quote from: frnkeore on June 08, 2021, 04:18:54 PM

Do you have a good milling machine and a good machinist available?

Yes, my son who is my partner in the project is a machinist and has his own Fanuc Robodrill CNC mill in his garage. It is a very accurate and capable machine. He also does all the computerized design stuff like cad cam or something like that. But his experience is industrial and aerospace, he know nothing about connecting rods.

SSdynosaur · « **Reply #4 on:** June 08, 2021, 07:05:42 PM »

Before committing to self-production you might ask Crower for a bid. I have "special ordered" 3 or 4 steel rod sets for NHRA racing and find their attention to dimensions and overall workmanship to be exceptional. Not the cheapest, by any stretch, plus, everything ordered during the current economic conditions is going to be a wait but that is common throughout the US industrial complex.

frnkeore · « **Reply #5 on:** June 08, 2021, 07:57:44 PM »

Ok, you will have to draw it up first. I'd use H11 or 4340 and you'll have to do some measuring for big end clearance and taper on that end, to be sure the beam clears the bottom of the bore, with the stroke your going to use, too.

You'll need to rough the part and HT, before finish machine work, too.

You'll have to know how your going to locate the cap, hollow dowels or shouldered bolts. Once it's drawn, he should know how to do the machining.
Do a search of connecting rod drawings and you should come up with something start with.

winr1 · « **Reply #6 on:** June 08, 2021, 08:00:37 PM »

Scat has some flat head rods around 7" for 599.00

Wonder if they could make a 9" rod economically ??

Is a 9" rod factory length for a 337 ??

Ricky.

machoneman · « **Reply #7 on:** June 08, 2021, 08:22:57 PM »

A wild thought: could an old radial aircraft engine or even a liquid cooled V engine have similar log rods. Have no idea about who supplies rods for really old aircraft engines but.........

Gaugster · « **Reply #8 on:** June 08, 2021, 08:56:27 PM »

Along those same lines....might want to check into any extra long diesel rods. Ideally finding the right length and then could be narrowed etc...??

428 GALAXIE · « **Reply #9 on:** June 09, 2021, 05:28:08 AM »

https://www.autoverdi.com/rods

blykins · « **Reply #10 on:** June 09, 2021, 07:39:18 AM »

There are several rod companies who will do customs. Molnar will, R&R, etc. R&R just made me a full custom set of aluminums for about $1200. They have the capability to do steel, titanium, and aluminum.

Hemi Joel · « **Reply #11 on:** June 09, 2021, 09:54:14 AM »

Thanks for all the great suggestions. I think I screwed up the math on the rod length. It should be 8.25". 12" deck height, 4.5 stroke, 1.5 compression height. If we do make our own, we could 3d print a plastic piston and rod to test fit and clearances.

What do you guys think of switching to a 2.55 compression height on the piston so I could use off the shelf 7.2" BBC rods? Will that be to heavy of piston, or other issues?

blykins · « **Reply #12 on:** June 09, 2021, 10:16:23 AM »

I personally wouldn't want a piston that tall/heavy.

frnkeore · « **Reply #13 on:** June 09, 2021, 01:27:06 PM »

I might be able to help you with old 6 cyl rods.

Chrysler and Dodge trucks with what was called 251, 253 or 253 eng, had 7 7/8 long rods.

IHC eng called U for tractors and BD for trucks, 269, 282 or 308 had 8 9/16 long rods.

Both have 2 1/8 crank pins. Big end width is 1 3/8 and 1 11/16 for IH

The MOPAR's have 55/64 WP & the IHC has 59/64

cjshaker · « **Reply #14 on:** June 09, 2021, 01:34:38 PM »

Flathead pistons are typically tall and heavy to start with. That would be a lot of added weight to an already marginal bottom end. And as you mentioned, with bores being so small, a mock-up with a plastic or wood rod would be essential before even trying anything. Personally, I'd be surprised if they fit without hitting the cylinder.

On the radial engines, while they do have long rods, they're only designed to run at 3500 RPM max. I'd imagine you'll be pushing your engine to 5500-6000 with a good bottom end. Well out of range of what radial engine rods are designed to run. I'd be surprised if you could find anything close to correct journal sizes anyway.

You mentioned adding extra crank supports. Are you narrowing the main and rod journals on a billet crank to make room? I'm really curious how you're going to accomplish this. Any way to post pics, or is this a top secret job?

Dumpling · « **Reply #15 on:** June 09, 2021, 01:46:25 PM »

What length were you being quoted on originally? 9" or 8.25"?

Isn't there some heat treatment/relieving done after machining the rods?

Seems like going cheap and dirty while everything else isn't. JMO

pbf777 · « **Reply #16 on:** June 09, 2021, 03:02:08 PM »

Quote from: machoneman on June 08, 2021, 08:22:57 PM

A wild thought: could an old radial aircraft engine...............

Quote from: cjshaker on June 09, 2021, 01:34:38 PM

On the radial engines, while they do have long rods, they're only designed to run at 3500 RPM max. I'd imagine you'll be pushing your engine to 5500-6000 with a good bottom end. Well out of range of what radial engine rods are designed to run. I'd be surprised if you could find anything close to correct journal sizes anyway.

Just a note: Apparently we're not familiar with the general engineering format of the typical "radial" engine, as this consists of a 'master' rod upon which then the other 'link' rods are attached, this permitting all pistons and rods in a singular radial cylinder row to be attached to the single crankshaft throw. This making some rather not compatible engineering for the typical V8 automotive engine format.

For a better description, with pictures just Google it!

Scott.

frnkeore · « **Reply #17 on:** June 09, 2021, 03:45:31 PM »

Quote from: Dumpling on June 09, 2021, 01:46:25 PM

Isn't there some heat treatment/relieving done after machining the rods?

All aircraft quality, steel parts are usually, started with either annealed or normalized material, then rough out, sent for HT, then finished machined, MPI and then plated, if needed. I never made any that plating, wasn't a spec.

Royce · « **Reply #18 on:** June 09, 2021, 05:24:47 PM »

Joel you might check with a materials engineer to see what kind of strength you need then select your material and dimensions..I think Bill Connely might be of some help there... Ted Eaton had Cunningham do a custom set of rods with offset caps after checking with several other rod mfg who really did not want the job... Titanium? I think if you cnc your own you are still looking at getting the proper heat treat and stress relief.. Check some Mercury Marine powerboat racing engines.. They have some big cubic inch stuff that would probably have tall decks and long strokes

Royce · « **Reply #19 on:** June 09, 2021, 05:29:39 PM »

Another thought.. Pulling tractors.. Those diesels have some honking long rods and I know the internals on some of those are all custom If you can contact one of the pullers in super stock class they might be able to point you to a source they use.. But really, a guy who owns a Duesie should be able to swallow 800 per rod LOL

jayb · « **Reply #20 on:** June 09, 2021, 07:29:18 PM »

That's right Royce, if he would just stop eating shrimp every night he could afford custom rods

(Sorry, that was an inside joke...)

cammerfe · « **Reply #21 on:** June 09, 2021, 09:38:41 PM »

There can't possibly be anything wrong with a guy that wants shrimp regularly. I know a place that offers all you can eat...
But that's another story!

KS

cjshaker · « **Reply #22 on:** June 09, 2021, 10:24:02 PM »

Quote from: pbf777 on June 09, 2021, 03:02:08 PM

Just a note: Apparently we're not familiar with the general engineering format of the typical "radial" engine, as this consists of a 'master' rod upon which then the other 'link' rods are attached, this permitting all pistons and rods in a singular radial cylinder row to be attached to the single crankshaft throw. This making some rather not compatible engineering for the typical V8 automotive engine format. For a better description, with pictures just Google it!

Scott.

Gee, considering I'm a vintage war plane buff, and have flown in multiple radial engine planes, I didn't even stop to think that a radial engine was designed differently than a water cooled V8. Thanks for pointing that out.

winr1 · « **Reply #23 on:** June 10, 2021, 01:20:48 PM »

I over looked this " This is for the blown 337 Lincoln flathead for land speed racing "

Since it will be blown, can the piston be below deck making the Comp height shorter ??

Also since the pistons need no valve reliefs the piston top can be only thick as it needs to be making it lighter

Have the pin bosses use a narrow wrist pin .... shorter skirt on non thrust side ..

What rpm will this turning if I may ask ??

Ricky.

Barry_R · « **Reply #24 on:** June 10, 2021, 09:44:36 PM »

R&R used to make custom steel rods, but I don't think they do them anymore. Last set were closer to two grand than to one grand and it's been many years.

You could probably make something out of 3/4 plate, but it would take a couple of minutes on the mill...

JERICOGTX · « **Reply #25 on:** June 15, 2021, 10:47:05 AM »

Quote from: Royce on June 09, 2021, 05:29:39 PM

But really, a guy who owns a Duesie should be able to swallow 800 per rod LOL

I don't know... He keeps losing dinner bets to me... LOL.

machoneman · « **Reply #26 on:** June 15, 2021, 05:29:23 PM »

Quote from: pbf777 on June 09, 2021, 03:02:08 PM

Quote from: machoneman on June 08, 2021, 08:22:57 PM
A wild thought: could an old radial aircraft engine...............

Quote from: cjshaker on June 09, 2021, 01:34:38 PM
On the radial engines, while they do have long rods, they're only designed to run at 3500 RPM max. I'd imagine you'll be pushing your engine to 5500-6000 with a good bottom end. Well out of range of what radial engine rods are designed to run. I'd be surprised if you could find anything close to correct journal sizes anyway.

Just a note: Apparently we're not familiar with the general engineering format of the typical "radial" engine, as this consists of a 'master' rod upon which then the other 'link' rods are attached, this permitting all pistons and rods in a singular radial cylinder row to be attached to the single crankshaft throw. This making some rather not compatible engineering for the typical V8 automotive engine format. For a better description, with pictures just Google it!

Scott.

RPM limits are noted. Yet, having 'done' my share of radial engines, some rods potentially (not the master of course) could be used. Yet, I'd not want to test the rpm limits of older design rods in my engines, just to be clear!

BigBlueIron · « **Reply #27 on:** June 16, 2021, 10:12:50 AM »

Good friend of mind builds tractor pulling engines. Makes his own rods, material is flame cut to a rough shape by a supplier and he does the rest in house. Not sure what the material is. I could ask if interested.

Hemi Joel · « **Reply #28 on:** June 28, 2021, 11:30:44 PM »

Quote from: winr1 on June 10, 2021, 01:20:48 PM

I over looked this " This is for the blown 337 Lincoln flathead for land speed racing "

Since it will be blown, can the piston be below deck making the Comp height shorter ??

Also since the pistons need no valve reliefs the piston top can be only thick as it needs to be making it lighter

Have the pin bosses use a narrow wrist pin .... shorter skirt on non thrust side ..

What rpm will this turning if I may ask ??

Ricky.

We plan to run 6500 rpm.

Hemi Joel · « **Reply #29 on:** July 31, 2021, 12:17:23 AM »

We have our first draft of a rod. Now we need to have it analyzed. It is a stretched version of an Oliver BBC rod. Cam has it all in a cad file. He put an Oliver rod that we borrowed from JericoGTX in his coordinate measuring machine, then manipulated it to make it longer.

pbf777 · « **Reply #30 on:** July 31, 2021, 07:02:15 PM »

Based on the picture, if crankcase, camshaft or whatever would permit it, I would want to adopt a greater taper in the beam, particularly being wider at the juncture of the big-end reducing the 'shoulders' or distance from the beam juncture to the bolt-posts; otherwise just additional heft to these 'shoulders' to reduce the tendency for the big-end I.D. to change dimension upon being loaded.

As for a rather exaggerated example, look at the Ford/Mercury M.E.L. 430/462 connecting rod. Though to much and one finds that in machining for the retaining bolt, one creates effectively a 'notch' this in particularly the "I"-beam flange,........not good!

As I often say: Just another comment from the peanut gallery!

Scott.

Hemi Joel · « **Reply #31 on:** August 01, 2021, 11:53:09 PM »

We will look into that idea, thanks

Hemi Joel · « **Reply #32 on:** August 03, 2021, 01:44:57 PM »

Quote from: frnkeore on June 09, 2021, 03:45:31 PM

All aircraft quality, steel parts are usually, started with either annealed or normalized material, then rough out, sent for HT, then finished machined, MPI and then plated, if needed. I never made any that plating, wasn't a spec.

FRNKEORE, could you tell me more about this MPI and plating process? I appreciate your input. Thanks, Joel

frnkeore · « **Reply #33 on:** August 07, 2021, 10:16:21 AM »

I'm sorry to be so late getting back to you.

All steel aircraft parts are magnetic particle inspected (MPI) and most all are cadmium plated. MPI is the same as "Magnaflux".

Hemi Joel · « **Reply #34 on:** August 09, 2021, 07:48:15 PM »

Thanks for the info Frank. Does that CAD plating serve any purpose other than corrosion protection? I don't think we need corrosion protection in the crankcase.

frnkeore · « **Reply #35 on:** August 10, 2021, 01:24:00 AM »

Yes, just basically corrosion protection

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Author Topic: How to build your own racing connecting rods? (Read 5234 times)

winr1

winr1