why not smooth casting surfaces on conrods and the crank?

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ELS
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why not smooth casting surfaces on conrods and the crank?

Post by ELS »

Wouldn't smoothing out the surface to a mere polish on things like the conrods, crankshaft, and even the block benefit by lowered windage for rods and crank, and less possible windage and faster oil return to the pan for the block?
I ask because I haven't seen anyone do this on stock cast parts.
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Re: why not smooth casting surfaces on conrods and the crank?

Post by mag2555 »

That’s why people who want every last bit of power will make a very close fitting custom crank scraper.

In terms of a V8 motor it’s faster to build such then polish the hell out of everything.

That being said I have polished the hell out of a few cast cranks in my time for strength reasons, not oil management.
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ELS
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Re: why not smooth casting surfaces on conrods and the crank?

Post by ELS »

mag2555 wrote: Thu May 26, 2022 6:59 pm That’s why people who want every last bit of power will make a very close fitting custom crank scraper.

In terms of a V8 motor it’s faster to build such then polish the hell out of everything.

That being said I have polished the hell out of a few cast cranks in my time for strength reasons, not oil management.
oh so like removing sharp features on parts so they don't become places for cracks to appear? I hadn't thought of that. :)

but I had a thought that couldn't a close fitting crank scraper add aerodynamic drag to the crank, in cases where windage isn't a big issue, like in dry sump systems for example.
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Re: why not smooth casting surfaces on conrods and the crank?

Post by GerryP »

In the old days...way before the Internet, we used to take those factory steel rods and polish them, then have them shot peened. They sure looked purdy before being peened. This was just to add strength to the rod and eliminate stress risers. We used to paint the valley and crankcase with glyptal to aid in oil drain back and to seal the casting from any grit shaking loose. Crank polishing isn't anything new. I never did it but I have seen them and they are pieces of art.
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Re: why not smooth casting surfaces on conrods and the crank?

Post by PackardV8 »

Not exactly new news. I've seen photos of racing engines from the 1920s to today where the builder polished all the internal parts; even the inside of the crankcase.
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Re: why not smooth casting surfaces on conrods and the crank?

Post by ELS »

oh, I thought those were all aftermarket billet cranks and rods
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Re: why not smooth casting surfaces on conrods and the crank?

Post by HQM383 »

It doesn’t work that way. You have what’s called ADHESIVE FORCES which is attractive forces between molecules of different types, fluid oil and metal in this case. A bead of water sitting on a vertical window pane that does not run down the window until it reaches a certain size with added water is a good example. The smoother the surface of the glass the more surface area of adhesion. A rougher surface will be less likely to hold the bead. Therefore polishing increases surface area leading to more oil attachment to crank and rods. The polished metal won’t fly through the oil unhindered or ‘slip’ on the oil as would be expected.
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: why not smooth casting surfaces on conrods and the crank?

Post by rebelyell »

By the same token, do you also assert that the smoother the surface, the more surface area it has?
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Re: why not smooth casting surfaces on conrods and the crank?

Post by HQM383 »

rebelyell wrote: Fri May 27, 2022 12:59 am By the same token, do you also assert that the smoother the surface, the more surface area it has?
Your right and I have used the wrong terminology in my haste. Greater surface area with rough surface. Better adhesion with smooth or at least the same. But, from what I understand material matters too so aluminum rods may have a different effect and coatings different again just like the different adhesion of a water bead on bare paint and wax coated paint. Water likes the paint but not the wax, not because the wax is smooth, but because the water and wax molecules don’t get along. Water cohesion is greater than water to wax adhesion and forms a bead. If you could get oil to bead on a conrod and crank surface then we’re on to something. Teflon coatings?

Considering all that it would be a lot of work in the hope for any appreciable gains. I wonder if anyone has done a controlled test with polished crank rods? I’d think if there were value in it we would see it more often.
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: why not smooth casting surfaces on conrods and the crank?

Post by 289nate »

GerryP wrote: Thu May 26, 2022 7:52 pm In the old days...way before the Internet, we used to take those factory steel rods and polish them, then have them shot peened. They sure looked purdy before being peened. This was just to add strength to the rod and eliminate stress risers. We used to paint the valley and crankcase with glyptal to aid in oil drain back and to seal the casting from any grit shaking loose. Crank polishing isn't anything new. I never did it but I have seen them and they are pieces of art.
Still works today.
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Re: why not smooth casting surfaces on conrods and the crank?

Post by David Redszus »

HQM383 wrote: Thu May 26, 2022 10:21 pm It doesn’t work that way. You have what’s called ADHESIVE FORCES which is attractive forces between molecules of different types, fluid oil and metal in this case. A bead of water sitting on a vertical window pane that does not run down the window until it reaches a certain size with added water is a good example. The smoother the surface of the glass the more surface area of adhesion. A rougher surface will be less likely to hold the bead. Therefore polishing increases surface area leading to more oil attachment to crank and rods. The polished metal won’t fly through the oil unhindered or ‘slip’ on the oil as would be expected.
Viewed from either end, as the crank rotates, it flings oil up one side of the crankcase and down on the oppposite side.
Which side of the case should we polish?

Perhaps the dimensions and shape of the rods and crank have a greater influence than does surface finish.
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Re: why not smooth casting surfaces on conrods and the crank?

Post by HQM383 »

David Redszus wrote: Thu Jun 02, 2022 12:48 am
HQM383 wrote: Thu May 26, 2022 10:21 pm It doesn’t work that way. You have what’s called ADHESIVE FORCES which is attractive forces between molecules of different types, fluid oil and metal in this case. A bead of water sitting on a vertical window pane that does not run down the window until it reaches a certain size with added water is a good example. The smoother the surface of the glass the more adhesion. A rougher surface will be less likely to hold the bead. Therefore polishing increases *the adhesion* leading to more oil attachment to crank and rods. The polished metal won’t fly through the oil unhindered or ‘slip’ on the oil as would be expected.
Viewed from either end, as the crank rotates, it flings oil up one side of the crankcase and down on the oppposite side.
Which side of the case should we polish?

Perhaps the dimensions and shape of the rods and crank have a greater influence than does surface finish.
If the end goal is to reduce drag through and pick up of the oil, then yeah.
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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