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Hi all. My name is Steve. I live in Phoenix, Arizona. I LOVE rebuilding British engines. This is my thread....













 

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Looks very nice and shiny.Just remember that the rough finish of the castings allowed a higher surface area for cooling so your engine will run hotter as a result of smoothing out the castings.I would certainly not polish internal parts as the rough surfaces allow cooling oil to cling on longer.
 

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The R/H case had been replaced. And after media blasting, the cases just didn't match in color. One was darker then the other. So the decision to polish the cases was made by the owner of the engine. I'm just the builder!!

I'm told it's a magazine build, so it might not get ridden that much.

Yes, you can send me your engines!
 

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Here we go again...

Rough cast engines run cooler than polished and a polished surface radiates less heat.

Sorry chaps, but these comments do surface regularly (and I had a guy at a bike show last weekend say the same thing to me about my engine), but no one ever produces any figures to back the statements up.

Facts please!

Mark
ps: Lovely engine!!!
 

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Here we go again...

Rough cast engines run cooler than polished and a polished surface radiates less heat.

Sorry chaps, but these comments do surface regularly (and I had a guy at a bike show last weekend say the same thing to me about my engine), but no one ever produces any figures to back the statements up.

Facts please!

Mark
ps: Lovely engine!!!
This is simply a matter of common sense. I'm sure we all agree cylinder bores and cylinder heads a are designed with fins to increase surface area to improve dissipation of heat. A rough surface has a greater surface than a smooth surface and will therefore dissipate more heat. How much more is the question. My guess is, a little more. I like the rough cast finish better anyway. Cleans up well with a scrub of 1890 formula Bon Ami. And Triumph liked the rough cast finish too - cheaper!
 

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You can read about the cooling of castings by manufacturers that confirm a larger surface area will cool better than a smaller surface area.It is a simple fact.A search or study will reveal all.Of course,i was taught this as part of my engineering course at my College during my apprenticeship back in the early 70s.
I doubt polishing a road going engine will cause a problem,however,look at any race engine and the crankcases are always left rough.MV racers are a prime example.
 

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Yes of course a larger surface area cools better, that is not in question.
But how much is the increase in the cast surface of triumph cases compared to polished and how much does that contribute to cooling, bearing in mind that only a small part of the crank cases are exposed to the open air. I doubt very much that there would be more than a few degrees. But where are the facts and figures!

I would also assume that race engine cases are left rough cast because it is cheaper to do so and they do not need to be as pleasing aesthetically as a road bike. No other reason. But again, we are allowing ourselves mere conjecture as to why this is as there is no supporting evidence.

Mark
 

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Hard to get facts on generalizations. Sure the polished piece won't dissipate heat as fast, but does it put it into a critical heat range, I doubt it. Are there any documented cases where a motor blew or damage was caused due to the polished finish, I doubt it. It would have been nice to have a test where temps were taken during normal use and then replicated after polishing to see what the temps are and how fast it cools.
 

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This excerpt from the research article shows that in the experiments reported on, surface roughness enhanced thermal conductivity by 63% on average. Obviously, this work was not performed on antique engine castings but the principle remains the same that surface roughness enhances thermal conductivity. These experiments demonstrate a dramatic improvement. Engine performance is the sum of many small enhancements and, based on this research, I will not be polishing my engine cases. That's my best guess.

"First of all, and more importantly, the rough surfaces made by direct metal laser sintering (DMLS) show an enhanced convective heat transfer. In particular, even though the average roughness is not the best parameter to scale the heat transfer enhancement (see next), as expected the rougher the better. For a more quantitative analysis, the experimental data of the smoothest m reference surface are reported in Table 4 and those of the roughest m sample #3 are reported in Table 5. Defining the heat transfer enhancement E as the percentage increase of the rough surface for convective heat transfer with respect to the smoothest reference (assumed representative of milling processes), the sample #3 showed a peak enhancement of 73% and an average of 63%. This is the best result achieved so far during the present activity. This enhancement could not be simply explained in terms of effective area increase, as visible in Table 2. Even though the results are still part of an on-going effort, because many process parameters might be explored, this result would be considered very promising in many engineering applications, including electronics cooling. In electronics cooling, in fact, a few percent of heat transfer enhancement may lead to material saving of heat sinks and hence a significant economical profit, in case of the production of large amounts of standardized products."
 

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Did Triumph use a formula for heat dissipation and build them to a critical point, I think not? They used the technology that said rough surface cools faster and black is more efficient. But does polishing the cases bring it to a point of failure? Can anyone really answer that? If a rough surface, for numbers sake, say 100 and point of failure is at 65, where does polishing fit in? is it 85, and still safe, or 40 where it isn't. These are the critical questions to be answered.
The test for electrical components may be skewed for our application.
 
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