F1 pankl conrod

[riff_raff]

Brian.G,

Don't mean to beat a dead horse on this topic, but I would disagree with Mr. Wolkner's explanation. While applying a given normal force over a smaller contact area would increase the interface unit pressure, it would have no real effect on axial separation of the mating faces, nor on the ability of that interface to transfer shear forces.

The same is true for serrations. The included ramp angle of the serration surfaces does indeed produce a greater surface normal force for a given axial bolt preload. But that surface normal force is also more quickly relieved when the rod loads reverse.

The only realistic approach to reducing fretting at the rod beam/cap joint is to design the joint with enough elasticity to prevent the fastener preload from being relieved under all operating conditions.

[xpensive]

Brian.G,

Don't mean to beat a dead horse on this topic, but I would disagree with Mr. Wolkner's explanation. While applying a given normal force over a smaller contact area would increase the interface unit pressure, it would have no real effect on axial separation of the mating faces, nor on the ability of that interface to transfer shear forces.
...

I concur Terry, separation between the mating surfaces is of course prevented by the preloaded Force, not Contact pressure.

But Herrn Wolkner works in sales so give him a break. (Sorry Don)

I still believe that the groove is there to ensure contact on both sides of the bolt, so that no convex contact phenomenon appears at high bolt-preoads, a metod widely used since the dawn of mechanical engineering when you think about it.

Actually, when this is a high-precision component, I would probably use some FEA to calculate a slight angle to be ground
on the contact-surfaces, all in order to assure perfect mating after a given preload.

[engineer_roy]

Brian G, most interseting thread with many differing inputs and much added value to the debate but I have an outstanding question which I didn't see an answer to.
There was suggestion than the cap should be tightened down onto mating faces with an inward "slope" so that the lower hoop was put into compression.
The materials used generally have greater strength in tension than in compression. Is there not a danger of allowing greater "Con rod" ovalling and stretch when going from compression to tension in the lower hoop as compared to starting in tension and increasing to maximum tensile strength?

[elmerfud]

This is effing BS! I've got one these rods and the wear patterns are not consistent with the milling marks and i should know, i'm a toolmaker, machinist and i've torn apart a lot of worn out machinery in my twenty odd years in the trade. Read the Smokey Yunnick books section on bearing failure, the sides at the split line buckle inwards and scrape the oil of the bearing and bang. This is why you paid $50 and not the $500 the part is really worth.

[elmerfud]

if i can find a pair of rod bolts and torque them to their yeild, i bet you that surface will be heavily bruised and the bore will be crushed out of round at the edges.

[Scuderia Nuvolari]

So the high grade steel rod bolts are much stronger than the alloy rods. OK so tighten the rod bolts until the rod cap seat mushrooms.
I don't understand what you are trying to prove to us. I'm not an engineer so please be gentle.

[elmerfud]

F1 technical only accepts images from a domain and will not let me paste directly a sketch i made to visualise, over it, you carry on thinking that slot is a magic trick of clamping. Why not try it in the next engine you build, that is if you have ever built one.

1/3/2012 - to update anybody who cared about my post, several had been removed due to off topic nature and tone. I do apologise to anybody whom i may have offended, some forums thrive on heated debate and arguments whilst others are a bit more 'serene' and less tolerant of 'tone'.

Pankl rods, nice.