I have a customer who wants me to machine him a set of connecting rods for a vtwin motor (it's a lawn mower engine). The stock rods are cast aluminum and he wants something stronger. There are some companies that make some aftermarket aluminum rods for motor similar to his but not for his particular motor. Has anyone made a set of rods before? I'm not sure what grade aluminum the stock rods are, Can I use 6061 or should I use 7075? Is there anything I should take into consideration before I start machining these..for instance, rod stretch, heat, etc...? The stock rods seem very cheap even for a 35hp motor.
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Machining a set of Connecting Rods?
- Thread starter dlenardu
- Start date
- Replies 23
- Views 15,955
cmailco
Hot Rolled
- Joined
- Aug 22, 2010
- Location
- Dallas, TX
The typical aluminum rod is forged from 7075 and heat treated to T6 specifications. Forging creates much more ideal grain-flow than a machined "billet" rod cut from sheet due to grain end exposure but I have to wonder how much it would matter in this type of application... not exactly my area of expertise.
The greater the weight in the piston, ring and pin assembly, the greater the stress on the rod but that goes without saying... you want to keep things 'light' and eliminate stress risers by polishing all surfaces.
As far as clearances, I think that's the tricky part; side clearance, pin bore, bearing and piston-to-head. Typically, automotive builds use .060 min. piston to head. I think this is an area where you'll want to cross-reference the aluminum parts you can't get for this particular app and use their recommendations.
Any way to use the other manufacturer's rods with a sleeve bearing?
Forestgnome
Stainless
- Joined
- Aug 2, 2008
- Location
- Californeeeah
I'm wondering why he thinks he needs something other than stock rods. Is he adding nitrous?
No, the other rods are completely different from this engine. I do know that they say they are "billet" rods, they do not say they are forged, but they do not say what material they are.
Forestgnome: LOL, close. He is using this motor in a atv buggy. He found a company that made a Cam for it and put it in but that is all they make for that motor. So now it wants more power and he is doing head work, larger valves, etc.. So he wants a stronger rod to handle the extra power.
many of the big manufactures will do custom conrods you never know they might have a perticular one off the shelf to suit your application....
S_W_Bausch
Diamond
- Joined
- Jan 15, 2010
- Location
- Indianapolis, Indiana, USA
He really doesn't care if you make the rods, but he most definitely wants YOU to WARRANTY the rods.
And he most likely wants you to compensate him for labor, gaskets, etc.
I say pass on it.
And he most likely wants you to compensate him for labor, gaskets, etc.
I say pass on it.
Iceman Motorsports
Cast Iron
- Joined
- Dec 26, 2006
- Location
- NW Ohio, USA
7078. He must have an oddball v-twin.
Midwest Super Cub
Lakota Racing
Home
www.iceman-motorsports.com
to name a just a few producing them plus loads of small guys
Midwest Super Cub
Lakota Racing
Home
www.iceman-motorsports.com
to name a just a few producing them plus loads of small guys
ray french
Titanium
- Joined
- Jun 17, 2003
- Location
- climax,ga. 39834
I have to agree with S_W_Bausch.The rods would need to be balanced in respect to the pistons and bearings assuming bearings are applicable in this situation.Stock rods should do fine unless this is some sort of special application.If it is special then he needs to seek out a manufacturer of rods for his app.
X-Y-Z
Aluminum
- Joined
- Sep 21, 2005
- Location
- NEW HAMPSHIRE
I would suggest having him buy OEM stock rods, dress them up on the belt sander (clean up the parting lines)...polish the whole part and shot then peen them.
Then replace the studs or bolts with hardened ones. shave the cap down a few thou and hone them.
Maybe enlarge, or at least chamfer the oil holes if they have them.
Last but not least balance them.
That should make them plenty good for whatever he is doing with it.
Then replace the studs or bolts with hardened ones. shave the cap down a few thou and hone them.
Maybe enlarge, or at least chamfer the oil holes if they have them.
Last but not least balance them.
That should make them plenty good for whatever he is doing with it.
X-Y-Z
Aluminum
- Joined
- Sep 21, 2005
- Location
- NEW HAMPSHIRE
OH yeah...forgot to add: make sure the governer or rpm limiter is set to stock RPM when this is all put back together...since this guy will want to 'see what its got', he will be over reving it given the chance. Overspeed would most likely be the first thing to kill a connecting rod in this set up.
hickstick_10
Stainless
- Joined
- Oct 26, 2009
- Location
- BC Canada
cmailco
Hot Rolled
- Joined
- Aug 22, 2010
- Location
- Dallas, TX
And I also agree... though it is often fun to talk about how things are made and making them ourselves.
Regards,
Chuck
Iceman Motorsports
Cast Iron
- Joined
- Dec 26, 2006
- Location
- NW Ohio, USA
And I also agree... though it is often fun to talk about how things are made and making them ourselves.
Regards,
Chuck
And also to see if we can destroy our work....and have a little fun in the process
H&J Productions
slufkin
Aluminum
- Joined
- Jun 19, 2008
- Location
- Upstate NY
Performance V-Twins
If he is working on a Briggs Vanguard, tell him to call Al Hodges at Performance V-Twins. I can't say enough good about this guy. I bought Billet AL rods from him for my sons Pulling Tractor along with a few other go-fast parts and it runs like a bear for not too much money.
Don't "shop" the website, call and ask for Al. He has built it...broke it...built it....repeat until it don't break no more.
Performance V-Twins
Of course, if you want to build the rods just for fun, I encourage you to do so. Go with the 7075 and let er rip. Experience is the best teacher for these things, just make it clear that there is NO WARRANTY on these parts, but if the guy is your buddy, I'm sure you will be fine and have a good time with the project.
If he is working on a Briggs Vanguard, tell him to call Al Hodges at Performance V-Twins. I can't say enough good about this guy. I bought Billet AL rods from him for my sons Pulling Tractor along with a few other go-fast parts and it runs like a bear for not too much money.
Don't "shop" the website, call and ask for Al. He has built it...broke it...built it....repeat until it don't break no more.
Performance V-Twins
Of course, if you want to build the rods just for fun, I encourage you to do so. Go with the 7075 and let er rip. Experience is the best teacher for these things, just make it clear that there is NO WARRANTY on these parts, but if the guy is your buddy, I'm sure you will be fine and have a good time with the project.
White Rabbit
Plastic
- Joined
- May 28, 2010
- Location
- Boston
You should suggest titanium rods. Lower thermal expansion coefficient that is closer to that of the steel wrist pin & big end (rather than Al).
Ti lawnmower rods, what not to like!
Well if you're gonna bother with the cost and the pain cutting Ti rods, why not use a stronger ferrous alloy and just cut them real thin. Hell, we're using inco 625 for rods in a BMW straight six... Its a real bitch but they're gonna be almost as light as the aluminums.
Fixed_Gear
Aluminum
- Joined
- Apr 30, 2006
- Location
- Toronto, Ontario
^^^
Ahh, the the new resident metals expert.
Ahh, the the new resident metals expert.
metlmunchr
Diamond
- Joined
- Jul 25, 2004
- Location
- Asheville NC USA
Have to agree. Why would anyone fight with inco 625 to end up with a part with 125Ksi yield strength max? You can beat that strength with 4340 any day of the week, and easily double it with any of the maraging steels which cut like butter compared to any inco alloy. Cutting titanium is also a walk in the park compared to high nickel alloys, not to mention equal or greater strength and less weight for the finished part.
The fact that an alloy performs well in a jet engine application really doesn't have a thing to do with its suitability for reciprocating engine parts unless someone's looking to run their grocery getter at a thousand degrees or more
GM uses Ti rods in the new 635hp ZR-1 engine, and when an engine is a $40,000 option there's plenty of money to use most any material they need to.
cmailco
Hot Rolled
- Joined
- Aug 22, 2010
- Location
- Dallas, TX
If I were in the market for an unobtainium rod material, hell I'd probably just opt for a super clean vacuum arc remelt, aka VAR4340.
By the way, Chevy has been using the Ti rods since the 05' Z06... though I seem to remember reading that they are powder metal. Cool stuff.
By the way, Chevy has been using the Ti rods since the 05' Z06... though I seem to remember reading that they are powder metal. Cool stuff.
metlmunchr
Diamond
- Joined
- Jul 25, 2004
- Location
- Asheville NC USA
Not sure about the Ti rods being powder metal. Could be. The rods in my 08 LS3 are powder metal 4340. The ZR-1 motor is based on the LS3 rather than the LS7, so I assume the Ti rods are interchangable between the two. I'd imagine they're a healthy chunk of change as compared to any other Chevy rod from the past, and I'm pretty sure I don't need a set of 'em
