My Own Pistons And Rods...

[nissan200sx.dk]

Hi.

Have just finished my education, FINALLY!!! And have gotten a new job with acces to much more "fun" machines. hehe.

Its basicly just draw it in solidworks, CAD/CAM, and make the part.

Sooo, i wanna make my own pistons and con rods.

Have thought of 7075 aluminium for the rods, but dont know what material for the pistons.

Rods are much more beefy than std rods, as they are aluminium so need to be bigger.

This design has been tested in COSMOS (in solidworks, with very high test loads) and it have been redesigned some times to get to this. In solidworks, with correct material inputted they can withstand over 2000nm of force down on them, and also in pull and twist.

They are not too wide so they will touch pistons when engine is turning, have measured and tested. The chamfer in the top hole for lubrication is a little bigger than std.

On picture the big ends bearing caps are not cut out.

Are there anything I should be aware of when building my own rods??

Now to the pistons... What material?

How about design?

[nissan200sx.dk]

How much does a single rod weigh? from say HKS..

[TheProDaniel]

Looks nice. I can't provide you with any information but I'll be keeping an eye on this thread as I've just finished my autocad and inventor modules in my course.

[nizmonut]

the last set of pistons and rods i bought from HKS were chromolly steel not alloy.

[Adriano]

Just bear in mind that you have to take into account the difference in thermal expansion between the conrod and the block when setting op your piston heights. Thats the main reason alloy rods aren't particularly popular.

[Roy]

Also, be careful with the modelling. Are you allowing for the lateral loads, intertia, cyclic stresses, heat etc etc Also how do you propose to make them, machinging from a billet i suppose? A set of aftermarket rods are already cheaper then the price you will pay for the billet you require to make the things

[Usual Suspect]

i would make the rods/pistons for a less expensive engine as practice.

or less vital parts first

[nissan200sx.dk]

I want to make them, because I can make them myself. This is one long learning process..... So they will be tested in a engine on a test stand first. hehe.

I know alu expans more, but there is ALOT of different alu.. Some expand more than others, and how hot is the rod going to be???? Recon it wont be hotter than the oil its covered with? Then its faily easy to calculate how much it will expand.

We have a danish dragster team, they have over 6000hk and have seen one of thier homebuilt rods. Its alu, and just much much more beefy. thats it. Like the one i have drawn, but mine is going NO WERE near 6000hk, its maybe going to take 1000hk. (This is far out in future dreams, if rods and pistons are made by me, and tested etc etc etc.)

Ï know aftermarket rods usually are somekind of steel... But they can be made in alu also.

My new company I work for make ALOT of aluparts for the military.. (also carbon parts for that matter)

Could rods be made in carbon? <-- crazy thougt?

If the say the lenght of the rod, this is way way overrated, would expand just 0.1mm. How much influence does that have???? Would recon nothing, as the squish is more than 0.1 mm, and piston to valve clerance is also bigger. (pistons could just be made with cut outs for valves if an issue)'

One more thing I havnt really gotten clearified is the design of pistons. They are not completly round, but how much?? I recon this has some corolation to how much it expans.?

(Sorry for bad english, some technical words im not sure of in english)

[nissan200sx.dk]

in relation to expansion... pistons is alu....

Rods are under them so should get alot LESS heat.

[Adriano]

The rods will definately get a lot hotter than the oil, the oil cools them. they are also a lot longer than a piston is wide, i would expect to allow .25mm for thermal expansion, which effects squish and comp ratio. I would get a forged piston and measure how much "barrel" shape it has. How do you plan on forging the blank?(ps you can buy forged blanks)

[**RB2530**]

Hi.

Have just finished my education, FINALLY!!! And have gotten a new job with acces to much more "fun" machines. hehe.

Its basicly just draw it in solidworks, CAD/CAM, and make the part.

Sooo, i wanna make my own pistons and con rods.

Have thought of 7075 aluminium for the rods, but dont know what material for the pistons.

Rods are much more beefy than std rods, as they are aluminium so need to be bigger.

This design has been tested in COSMOS (in solidworks, with very high test loads) and it have been redesigned some times to get to this. In solidworks, with correct material inputted they can withstand over 2000nm of force down on them, and also in pull and twist.

Dood,

You are keen!!

Just a couple of things though...2000Nm (always need to pay respects to Isaac Newton and use a capital N) is a torque or torsional force. Linear force is measured in Newtons or (N) Anway just wondering how you got this number....Is it from a static or dynamic calc...

When I was at uni I did a conrod design project and found that the dynamic stresses far outway stresses caused by gas pressure on the rod from the piston...These stresses increase with rpm and the relationship is pretty much a squared one...ie if you double the engine rpm, the conrod stresses increase by a factor of four...I also worked out that the highest stresses are tensile and experienced just after TDC on the inlet stroke...The reason for this is that the rod has to accelerate the piston mass, overcome piston friction and also draw in the air fuel mix...This force is by far the highest when engine is at full rpm and the throttle is closed suddenly producing high cylinder vacuum. This is why good rod bolts are so important cause the tensile stress in the rod bolts can be absolutley huge and get much much higher as rpm increases...

On the power stroke the mass of the piston causes a tensile stress in the rod but the gas pressure produces a compressive force...these forces then start to cancel out and the resultant force is less....

You also need to consider bending in the rod...the angular acceleration of the bigend compared to the little end is huge as well so the rod has to be stiff enough resist fatigue due to cyclic bending..eg the use of H-beam rods that have high stiffness across them...

Anyway mate good luck with it but I would really recommend you try the rods and pistons out in a crap engine first...

[**RB2530**]

Just remembered that you also should use a material that has a relatively high elastic modulus because conrods stretch elastically due to the high tensile load and which means they come higher up in the bore with increasing rpm....they also get shorter at bdc but this has less impact...obviously...the hisgher the elastic modulus, the less they stretch...