Ball Burnished Cases

by **Skyguyz** » Mon Jan 16, 2012 9:28 am

Tintin wrote:
Skyguyz wrote:Aerodynamic influences/boundary layer? Do explain?

A rough surface will create a larger boundary layer than a smooth one - and heat transfer happens mainly in the boundary layer. In order to be able to work properly a cooling fin needs enough aera to transfer the heat and enough boundary layer volume to dump the heat into. Both is changed by polishing and IMHO the change is for the worse.

Tim

The fins on a Norton are so rough to begin with. and ball polishing them slightly as to have an actual aerodynamic effect is remote. The boundary layer in aerodynamic terms is relative to the surface and increases rapidly with distance from the surface and the flow is laminar. I question the real possibility that polishing the fins on a Norton will change the the boundary layer smoothness as to have an actual aerodynamic effect that is worth mentioning.

Just saying.

by **enekoizagirre** » Mon Jan 16, 2012 9:38 am

I agree with Skyguyz...

by **Tintin** » Mon Jan 16, 2012 9:41 am

Skyguyz wrote:I question the real possibility that polishing the fins on a Norton will change the the boundary layer smoothness as to have an actual aerodynamic effect that is worth mentioning.

Judging by the visual difference (and I've seen heads which have been polished far more than this one and an ISF treatment will end up in a far smoother surface again) I don't agree about it not being worth mentioning - but as far as polishing parts is concerned we obviously have different opinions anyway.

Tim

by **slimslowslider** » Mon Jan 16, 2012 9:56 am

As far as optimising heat transfer, I reckon you do not want any boundary layer at all, you want turbulent flow at the least.

http://en.wikipedia.org/wiki/Turbulence

by **Skyguyz** » Mon Jan 16, 2012 10:00 am

Tintin wrote:
Skyguyz wrote:I question the real possibility that polishing the fins on a Norton will change the the boundary layer smoothness as to have an actual aerodynamic effect that is worth mentioning.

Judging by the visual difference (and I've seen heads which have been polished far more than this one and an ISF treatment will end up in a far smoother surface again) I don't agree about it not being worth mentioning - but as far as polishing parts is concerned we obviously have different opinions anyway.

Tim

The resulting boundary layer separation in this case is nil. If the fins were a airfoil shape then the case would have merit. The fins here are parasitic drag producing and the laminar flow is turbulent at best. Just my opinion.

*The difference of opinion of polishing parts for aesthetics is another topic and doesn't apply, agreed

MASc
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by **Hegel** » Mon Jan 16, 2012 10:13 am

Uh oh....Does that mean we need a NACA profile on our cylinder heads? :shock:

If that's the case, then what effect will a liberal coating of PJ1 have on barrels and head?

by **rpatton** » Mon Jan 16, 2012 10:47 am

Luckily for us, I don't think the Commando motor is teetering on the knife edge of disaster as far as the ability to shed heat goes. The production of heat is directly related to horsepower and most of the time we are riding around on 20-25hp. That raging 45hp at our disposal is 7000rpm at WOT.

I like the effect of burnishing for cosmetic reasons and corrosion resistance. The parts probably will be easier to keep clean and a little tougher against the rot from abrasion and moisture that I see on the forward facing surfaces on all the aluminum parts on my bike. I think that the high luster on the parts now will be tempered after 3-4 washings but it may still be tougher than rough castings.

by **hobot** » Mon Jan 16, 2012 11:00 am

The issue with Nortons is not the fin surface area which it has plenty to sit still on low power and not over heat in summer time, but more how much a mirror smooth finish there is to act as reverse mirror to reflect IR photons back inside instead of out to the breeze. Because Norton has excess fin area for its intended fueling heat ya can get away with a mostly mirror engine, until ya hop it up and really burn some fuel through it. Harley vendors sell a diamond pattern shiny saw tooth cut for fin edges which they claim increases heat dump but mainly its for looks and a mean process to handle w/o skin cuts or marring the show off sparkle texture.

PJI or even powder coat is a non heat issue in regular set up and run Commandos.
Pump em up for race power and use it - then may run into heat pile up issues on a long run at WOT if too polished.

by **beng** » Mon Jan 16, 2012 11:03 am

Apparently I go with Hobot this time.

The reason this ball-burnished engine would run hotter has nothing to do with airflow or surface area, it is simply because a polished and/or light colored surface is much worse at getting rid of heat than a non-polished and/or dark colored surface.

The bare casting that will radiate heat the best will be one with the castings in original condition, not polished, burnished etc..

Getting a dark color on the casting can help, but it can be overdone. A dark anodizing on alloy or very thin coat of stove-black on an iron cylinder will do the job. Powder coating your entire engine is like wrapping it in insulation.....

by **Tintin** » Mon Jan 16, 2012 11:21 am

slimslowslider wrote:As far as optimising heat transfer, I reckon you do not want any boundary layer at all, you want turbulent flow at the least.

If you can explain to me how there might be turbulent flow without a boundary layer I might understand this remark...

Tim

by **slimslowslider** » Mon Jan 16, 2012 2:46 pm

Tim, I took it you refered to laminar flow, if you meant turbulent, fair enough.
Turbulent it will be, when riding and where air has good access.

by **DogT** » Mon Jan 16, 2012 4:18 pm

I remember one time I had a radio with lots of tubes (valves for you UK fellas) in it, and there were metal shields over the tubes, so sort of shiny. I painted the tube shields black and I couldn't believe how much cooler the tubes were, you could touch them with the flat black paint on the shields. Without they were so hot you couldn't handle them. Color does make a big difference in radiating heat, but on the Norton, it's probably not such a big issue since most of the time you're going down the road and there is plenty of air circulating. I would doubt if you could make the barrels or head so shiny that the heat doesn't get dissipated. It's probably the same argument about powder coating the engine parts.

Not that I would do that.

Dave
69S

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