Topic: design and CNC custom rods??

[jaguar]

Im working with solid works alot in school and have made a few contacts with CNC guys that have made a few custom parts for different school projects.
what would it take to make a connecting rod?  
im looking for something for my cb125 LSR bike that im starting to get very into now.  the rod is my weak link as far as i can figure right now.
anyone have any experience making one off motor internals?
would it be any different then making any other part?  
was thinking 7075 but not really sure.

thanks for any help  

[754]

 Split rod or 1 pce ?
 1pce is pretty easy, even on manual equipment, as long as it uses a pressed in race.

 go for it.., but build more than 0ne..

[jaguar]

it would be a one piece part.
right now the stock rod uses a roller bearing, but think that a plain bearing would be better. but i really dont know.

anyway
what material would you use?
tips on cutting the part?
where would you look to find bearings?
guess the other question is why havent i seen more people doing it?  i understand that not everyone has autoCAD or a CNC but still.


the goal is to have a cb125 that is built for high RPM and will hold together with 25hp+ boost down the line.
i figure a "buillit" rod will be stronger and lighter then the stock

[Doctor_D]

7075 will work, and 2024 is nice stuff for your application as well.  The latter isn't weldable, so you don't see it as often, but it has excellent resistance to stress corrosion.

Don't forget 6Al-4V Ti.

[754]

Sounds like you have a press together crank, usually, or on some there is a pressed in outer race that is hardened, if you have that the job is easy.
 I think the 7000 series or 2024 would work, but may have shorter life than steel.. pay attention to grain direction when curtting out a blank.

 Easy way to cut out blanks these days is waterjet.. But once its fixtured and ready to cut, on a CNC, removing outer excess material if you sart with a rectangular slab, will still be pretty quick.

[MRieck]

The Japanese using very specific hardening techniques to one piece rods . This is especially true for the big ends. Something to keep in mind.

[jaguar]

what do you mean by that?
that deals with the stock rods?
we have been thinking about Ti but not sure about the tooling needed to make it work

yes the crank is a press together with a needle/roller bearing in the big end

[MRieck]

what do you mean by that?
that deals with the stock rods?
we have been thinking about Ti but not sure about the tooling needed to make it work

yes the crank is a press together with a needle/roller bearing in the big end

I mean the big ends have to be very hard when using roller bearings. I guy I know that has done many Funnybike roller cranks uses only OEM Suzuki rods.

[jaguar]

would it need to be a roller/needle bearing?  what are the pros and cons to them?
that treatments would the 7075 need or the Ti?

[754]

 Basically, the needle bearing run in a hardened outer race.. on some rods, it is a press in race, some the rod itself.
 If you used say chrome-moly you could perhaps heat-treat to the correct hardness. The other option is make a hardenable race and shrink into an aluminum or Ti rod and re-hone/lap to fit.

 To start the process, take a stock rod running surface, and get it hardness tested, to see what you need to end up with.. you may have to cut a rod to do this.. If its going to be done, and you want it to work.. there are no shortcuts..

[MRieck]

 I very good friend of mine who does all my balancing has seen more Carrillo 1 piece rod failures than OEM. Hardened inserts etc do not last. Falicon 1 piece rods do not last. All the professionals use OEM Suzuki rods...even in Kawasaki based engines.The copper on 1 piece OEM rods is there to shield the rod during heat treating on the big/small end. You do not want the rod beam beam to be as hard a that big end/small end. Anybody that has worked with OEM 1 piece rods knows this "copper" color.

[Ricky_Racer]

Any additional info out there on using Suzuki rods? Model? Sizes? Mods needed?  Thanks!  RR

[jaguar]

Yeh any more info about that?
If I could make an oem rod work I would rather do that then make my own.

Also for my motor we are just looking to hold 20ish hp na and maybe 25 under boost
So no where near what funny bikes are doing

[Big Jay]

Most of the roller bering rods are 8620 and carburized. Copper is a masking agent when carburizing. You machine the part, then copper plate it, then machine away the copper in the areas you want to have high surface hardness ( case hardening ). All of the real high end motocross bikes run Carrillos. I have never seen a broken one.

Back in the 80s, I made a set of aluminum rods with steel inserts for as top fuel roller bearing Kawasaki. They worked very well.

Jay

[754]

Are you sure stock is not up to snuff? I mean blowing up a 125 should not hurt as much as blowing up a 970cc motor..

 I got a plan on how you can do this reasonable, get a few stock rods. Cut one off about 1/4 inch above big end, dont use a torch or abrasive cutoff saw, it can cause hard areas.
 Turn a  stub arbor on the lathe, and do not remove, you want it to be true and a slip fit to the rod bigend ID. This stub should be around, 30 thou shorter than rod width, tap the middle of the arbor to at least 3/8 NC.
 Slip the cutoff bigend onto arbor, then secure with thick washer and bolt. Now you can carefully turn off most of the material, around the hardened race, you should end up in the neighborhood of .070-.090 thou thick.. if you start seeing shiny spots you are getting into the hardened area, good time to stop.
 You will need a fine finish on the OD, should actually be ground if at all possible..

 Presto.. hardened rod race to press into custom rod, with known to be adequate hardness.
 Next problem, can be tricky calculating press fit, if you are good you can get it bang on, if its tight, you can hone/lap the ID or remove from rod , and hone out from the rod.

 HD uses laps to resize their hardened pushin races, not sure if the size range covers yours.

 The other option, get some 8620, turn your own, heat treat and size properly..

 I think by now you may realize why there is not lots of people making their own rods!

[Big Jay]

If you are just going to make races from scratch, I would use 52100 which is ball bearing race material. You would have to ID grind them after heat treat.

There was a guy building a top fuel bike using a roller bearing set up ( which doesn't work with nitro ), and he wanted me to make a set of aluminum rods with the steel races so he could have them installed on the crank.

I persuaded him not to do it that way. If he insisted in the roller bearings, I told him to just make 52100 races and have them installed on the crank. Then have Super Rod make bolt on aluminum rods. This way he could change out the rods without having to disassemble the crank. That part worked very well. The bearings still couldn't stand up to nitro.

[Sam Green Racing]

Jay, I loaded similar period stock Honda rods and roller bearings by mistake with 100% nitro.
It ran off load but wouldn't pull under load there was a lot of eyes smarting and you couldn't breath within 20 foot of it. not blown and no harm done.

Sam.

[Big Jay]

Nitro hammers the bearings. On a roller bearing, it pounds the rollers into the crank pin. That is why all nitro bikes use plain bearing cranks and aluminum rods.

[Sam Green Racing]

Rick Stetson showed me a rod that had had the piston forced down over it, the rod was in tact but the piston pin ends were pointing downwards at about 45 degrees, nasty stuff that nitro.

Sam.

[BLUE71TURBO]

 AH YES !  NITROMETHANE !   

                       

[Ricky_Racer]

BIG cajones!     RR

[Sam Green Racing]

and that's one of the slower ones Ted.

Sam.