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SouthBend9
02-05-2008, 10:05 PM
Has anybody designed and machined your own special case connecting rods for an engine that they needed them for? I have and older tractor 4 cly. motor that needs and overhaul. My rods are twisted a bit an I thought I would machine my own set out of aluminum alloy. But I was hoping some you might have and would share some advice and what went well and not so well.
What aluminum alloy did you use ? Such as 6061
How you cut your caps ?
What was the crush of the sleeve bearing into the rod?
Thank you

CCWKen
02-05-2008, 11:41 PM
I've never made full size engine piston rods but I know that you don't want to use 6061--Even for a lawnmower engine. You'll probably need something in the 7000 series and you may still need to increase mass. I made racing rods for pro-kart engines way back. IIRC, the alloy was something like 7075? or 7045. What kind of length, horsepower and RPM are you talking about?

By the way, forged steel rods in those old engines can be cold-straightened. You might be better off building a straightening jig. Don't heat them or they'll warp when cooling and you'll be worse off than when you started.

neonman
02-05-2008, 11:44 PM
Southbend9, What are the original rods made of? For a restoration like that, I'd do a bit of research before I made new rods out of aluminum which was not die cast. Aluminum can fatigue and fail under the conditions a con rod is under if the material/cross section is not right. You could do grave damage to your engine if a rod failed.

Have you considered steel?

neonman

torker
02-05-2008, 11:52 PM
If your old rods where steel and you are to replace them with alu...even a simple engine like that would need to be rebalanced I bet.
I haven't built any alu rods but I've gone through a few sets in my 572 Rodeck blown alky motor. They are indeed 7000 series rods. Of course...your hp requirements may be a little less :D
Russ

wierdscience
02-06-2008, 12:41 AM
Straighten the twist and have them reconditioned.It costs $25/rod here to have it done.

Most aluminum rods I have seen are forged,something most HSMer's aren't setup to do.

CCWKen
02-06-2008, 02:46 AM
If your old rods where steel and you are to replace them with alu...even a simple engine like that would need to be rebalanced I bet.
LOL... I'm bettin' it has cast iron pistons and a flywheel the size of your tires! :D

Oldbrock
02-06-2008, 02:52 AM
find an engine shop and have them straightened and resized, shouldn't cost much. I never reuse con rods without resizing them-any con rod.Peter

torker
02-06-2008, 10:01 AM
Most aluminum rods I have seen are forged,something most HSMer's aren't setup to do.
Darin, the "good" rods are "plate" rods. They ummm...machine them out of 7055-T6. Yes, yes I know... that makes them billet of course. My experience with alu rods... they are a pain in real life. At least in this application. I could never afford to throw them out like the big boys do so I had to measure them for stretch at least twice per season. (Every ten passes or so). Each rod had it's own set of records. All very time consuming.
Ken...lol! Ya I'm always thinkin of the hi rpm newer stuff. Prolly wouldn't matter in that case.
Russ
(It just dawned on me... I used to have "time" to do dumm stuff like measure rods for a hobby. Wonder what happened there :D )

Bill Pace
02-06-2008, 10:14 AM
(It just dawned on me... I used to have "time" to do dumm stuff like measure rods for a hobby. Wonder what happened there :D )


Well, thats easy to answer.... youre now a succesful, prosperous, thriving businessman (with real employee/s, -- and making additions!) You aint got TIME for no stinkin childish hobbies!!

SO THERE!!

SouthBend9
02-06-2008, 06:04 PM
This motor is a 113 cubic inch. It is 3 in. bore and 4 in. stroke. It is rate 20 hp at drawbar and 23 at the pulley. The engine is governed and set at 1800 rpm .
It has forged steel rods now. They can be purchased at reconditioned at $45 a unit.
I was hoping to get a little extra poop! By making them out of aluminum. I thought that would help at the tractor pulling . So I asking the questions before I put all that work into this motor and blow it up in front of everybody.
God forbid It hurt somebody.

As you may know these motor can build up alot of stress just like race cars pulling weights or the tractor. The tractor weighs 3000 lbs and can pull maybe 3/4 to 1 1/2 times its weight so that 6000 lbs dead weight at the finish.

Gosh thanks for the help , any more thoughts ?

torker
02-06-2008, 07:20 PM
In this case the only reason you would want alu rods is to lower the rotational mass. This would normally only be done to increase the chances of survival at higher rpm. I'm not sure you'd see any benefit from that in this low R motor.

wierdscience
02-06-2008, 09:40 PM
Never seen anyone replace rods in an old tractor,but I have seen iron pistons replaced with aluminum,especially on engines that use babbited rod bearings.In that case significant wear reduction on the rod and main journals is the benifit.

BobWarfield
02-06-2008, 10:21 PM
They warn the hot rodders off aluminum for durability reasons last I heard. The sports car crowd I run with all like steel: Carillo being the best. The drag racers liked aluminum for the lower mass, but even more because it would soak up the knock from detonation on a blown motor. Life on rods in that application was extremely short.

The real expensive rods on real high rpm motors are usually titanium. NSX was the first to do that on the street I think, but they're common now for high end exotica.

Not a good street alternative!

Pistons, OTOH, benefit greatly from being aluminum in most applications. Their heat properties are ideal.

But why not consider steel if you want to make a set of rods? Better yet, find some rod that is close in dimensions and dirt cheap and use your machine shop to adapt the two ends to a diameter that works for you. Ideally, you find a rod where the holes are too small and you can bore them out.

It would have to be a labor of love versus just shelling out for new rods.

Best,

BW

SouthBend9
02-07-2008, 11:00 PM
From the poste2 I think that will recondition the stock con rods. From what I see it doesn't have much merit to go though all that work for nothing.
I think that balencing has merit.
Anybody know if they static balence the components of the engine and then dynamic balence the assembly ? I don't know much about this. I like to learn about it. Is it going to give a low rever like my 1800 rpmer a 5 % help or a 30 % help .


















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