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Fri Oct 05, 2012 2:43 pm

I'm ready to re assemble the top end on my 2007cc (90.5's) streeter sand rail engine, hone and re ring.

What's the current wisdom on painting the heads and cylinders with a light coat of high temp black?

Everything is freshly bead blasted and de greased.

Thanks, Paul.

Fri Oct 05, 2012 3:07 pm

i have never seen heads painted ever? cylinders yes a light coat is fine. don't know why i never seen heads painted? harley davidson has done it. my old 84 honda xl350 was painted? both air cooled. i say do it! i think no one does it cuz you really can't see them? ya if you crawl under the car you can see a tiny bit? i may help cooling? that's a whole other debate.. wont hurt anyway.

Fri Oct 05, 2012 3:08 pm

Many have found a light coat of paint on the cylinders doesn't hurt cooling too much, but painting the heads is likely to be a bad idea.

Any paint is going to be a bit of an insulator - the cooling is achieved through conduction to the air flowing across the fins and even if you improved radiated heat loss through a black paint it would be more than offset by the loss of conducted cooling.

You can't see most of the head - do a nice paint job on the tins and valve covers instead.

Fri Oct 05, 2012 3:21 pm

heads are non ferrous... they don't rust. why paint?

Fri Oct 05, 2012 3:25 pm

Cylinders are painted to keep from rusting. Heads are aluminum. Any paint on them will only act as an insulator making them run hot. Cylinders are only painted with very light coats of paint to minimize insulating properties.

I would however like to see if anodizing heads black would help with thier cooling properties though.

Fri Oct 05, 2012 3:27 pm

there goes the debate! it wont hurt but you cant see them so why ? harley and honda air cooled motorcycle engines have painted heads? i've built harley engines with powder coated heads with no problems? and they don't have a fan cooling them.they don't run any hotter.

Fri Oct 05, 2012 5:29 pm

Just because you can't measure something it doesn't mean it isn't there.

A lot of testing has been done on the effects of painting heatsinks - in electronics you will find untreated heatsinks for fan cooling, anodised for rediant cooling, and paint or powdercoating for marketing.

The value of anodising (which is really a method of applying a very thin paint which is bonded to the aluminium) has been hotly debated for many years, as even without fan cooling convection tends to play a part in the cooling.

Sometimes paint or powdercoat is used as it makes people buying high end gear feel they are getting better value for money, and in amplifiers and such you can always fit a larger heatsink to make up for the loss of efficiency with a larger heatsink and more fins - it will probably look better. We don't have the luxury of being able to do this with our heads.

Anodising doesn't take well to our heads - it has been tried. If you polished the heads up enough to get a good coating you would lose more efficiency than you could ever get back.

Contrary to what you may hear you can easily setup a valid exeriment to prove that a powdercoat or such will harm cooling efficiency. The cheapest way to do this is buy a couple of untreated heatsinks, drill a small hole for your thermocouple then paint one. Attach the two to an appropriate heat source - 5 - 10 Ohm Wire wound ceramic resistors in series across a car battery should do it. Blow a fan across both and compare the temperatures. If your meter isn't accurate enough you can play around with fan speed and amount of heat, you will find the naked heatsink will always be cooler to some degree though.

There are many other ways to test for this, just don't fall for the trap of measuring the surface temperature and thinking the coated head or heatsink is running cooler - remember it is being insulated by the paint!

Fri Oct 12, 2012 2:43 pm

Welp, I chewed thru all the offered data, and a bit more as well. I shot a lite coat of hi temp black on the cylinders and left the heads bare.

I was hoping to hear from sombody that tried coating the heads, but "it is what it is" I guess.

I did discover that the heads will take to a process called Alodyne, But it's more of a topical/shallow dye process as opposed to a surface penetrating, molecular transfer, anodize bath. It is supposed to close the pores and stop surface oxydation. Any body else heard of it?

Thanks for the discussion.

Paul

Fri Oct 12, 2012 3:46 pm

There have been advancements in paints or "coatings" that will aid in Thermal dispersion. Paints with High Aluminum and Silicone content are known to improve heat dispersion and recently some testing on nanostructured coatings have produced a "heat transfer coefficient" ten times higher than with the uncoated surfaces, dissipating heat four times faster than previously possible.
Surprisingly, the principles that brought the performance improvement are simple, and consist of covering standard heat conducting materials (such as copper and aluminum) with a thin strate of zinc oxide. The coating develops a multi-textured surface that encourages heat to be transferred via capillary forces.

Cerakote makes a heat dispersion coating that is a solid film lubricant. It has been proven to increase heat transfer to the air at a rate of 10-15% over bare metal surfaces lowering operating temperatures.

Something to think about

Fri Oct 12, 2012 3:48 pm

red caddy wrote: . I shot a lite coat of hi temp black on the cylinders

Whoops. Hi-temp paint has ceramic in it which is an insulator. Just regular cheap semigloss is the way to go.

Not worth re-doing them. But next time don't do hi-temp if you're looking for every little bit to help.

Fri Oct 12, 2012 4:32 pm

Depends what kind of high-temp paint - The trick with any paint in this application is to thin it before application, both to leave a thin coat, and to be sure it can get around the nice rough surface.

Fri Oct 12, 2012 4:33 pm

Lots of claims but Ive seen nothing that makes much of a difference. Most coatings that claim high heat transfer rates are based on sunlight frequencies. Not thermal frequncies. The best surface is a clean non coated surface. Dosent matter if it is aluminum or cast iron. Anything you put on top of it will block heat transfer in the thermal range. The cast iron cylinder is painted to keep it from rusting. The oxides will reduce the surface area and are highly resistant to heat transfer.
Just keep it clean and you will be fine. By the way. Anodizing creates a oxide surface too.so it reduces the heat transfer by oxidation and also by reducing the surface area by making the surface smooth.

Dyno-Don wrote: There have been advancements in paints or "coatings" that will aid in Thermal dispersion. Paints with High Aluminum and Silicone content are known to improve heat dispersion and recently some testing on nanostructured coatings have produced a "heat transfer coefficient" ten times higher than with the uncoated surfaces, dissipating heat four times faster than previously possible.
Surprisingly, the principles that brought the performance improvement are simple, and consist of covering standard heat conducting materials (such as copper and aluminum) with a thin strate of zinc oxide. The coating develops a multi-textured surface that encourages heat to be transferred via capillary forces.

Cerakote makes a heat dispersion coating that is a solid film lubricant. It has been proven to increase heat transfer to the air at a rate of 10-15% over bare metal surfaces lowering operating temperatures.

Something to think about

Fri Oct 12, 2012 4:58 pm

Current research at Oregon State University and at the Pacific Northwest National Laboratory suggest otherwise which is where my previous comments came from. I will have to dig deeper to remember where the paper was that I read about these studies.

JoeD wrote: Lots of claims but Ive seen nothing that makes much of a difference. Most coatings that claim high heat transfer rates are based on sunlight frequencies. Not thermal frequncies. The best surface is a clean non coated surface. Dosent matter if it is aluminum or cast iron. Anything you put on top of it will block heat transfer in the thermal range. The cast iron cylinder is painted to keep it from rusting. The oxides will reduce the surface area and are highly resistant to heat transfer.
Just keep it clean and you will be fine. By the way. Anodizing creates a oxide surface too.so it reduces the heat transfer by oxidation and also by reducing the surface area by making the surface smooth.

Dyno-Don wrote: There have been advancements in paints or "coatings" that will aid in Thermal dispersion. Paints with High Aluminum and Silicone content are known to improve heat dispersion and recently some testing on nanostructured coatings have produced a "heat transfer coefficient" ten times higher than with the uncoated surfaces, dissipating heat four times faster than previously possible.
Surprisingly, the principles that brought the performance improvement are simple, and consist of covering standard heat conducting materials (such as copper and aluminum) with a thin strate of zinc oxide. The coating develops a multi-textured surface that encourages heat to be transferred via capillary forces.

Cerakote makes a heat dispersion coating that is a solid film lubricant. It has been proven to increase heat transfer to the air at a rate of 10-15% over bare metal surfaces lowering operating temperatures.

Something to think about

Fri Oct 12, 2012 5:37 pm

:D
I used to be one of those researchers for 40 years. My doctorate is in Wave and Particle physics.
There are many considerations to be made (guessed at) in this line of work.
Pure metals are the most conductive materials. Even if you use pure metals in a coating you will always have layers of some non conductive material in between. Either oxides or some sort of polymer these days. It will create a thermal barrier and cut the amount of heat conducted drastically.. Most of the time it really makes little difference in the actual conditions encountered in the real manufactured product. They are always designed with a large safety margin to take these things into account.
If you are really interested in this and have decent math skills you can play with this yourself using Openfoam CFD. It is a free downloadable CFD program. Works quite well too.

Dyno-Don wrote: Current research at Oregon State University and at the Pacific Northwest National Laboratory suggest otherwise which is where my previous comments came from. I will have to dig deeper to remember where the paper was that I read about these studies.

JoeD wrote: Lots of claims but Ive seen nothing that makes much of a difference. Most coatings that claim high heat transfer rates are based on sunlight frequencies. Not thermal frequncies. The best surface is a clean non coated surface. Dosent matter if it is aluminum or cast iron. Anything you put on top of it will block heat transfer in the thermal range. The cast iron cylinder is painted to keep it from rusting. The oxides will reduce the surface area and are highly resistant to heat transfer.
Just keep it clean and you will be fine. By the way. Anodizing creates a oxide surface too.so it reduces the heat transfer by oxidation and also by reducing the surface area by making the surface smooth.

Dyno-Don wrote: There have been advancements in paints or "coatings" that will aid in Thermal dispersion. Paints with High Aluminum and Silicone content are known to improve heat dispersion and recently some testing on nanostructured coatings have produced a "heat transfer coefficient" ten times higher than with the uncoated surfaces, dissipating heat four times faster than previously possible.
Surprisingly, the principles that brought the performance improvement are simple, and consist of covering standard heat conducting materials (such as copper and aluminum) with a thin strate of zinc oxide. The coating develops a multi-textured surface that encourages heat to be transferred via capillary forces.

Cerakote makes a heat dispersion coating that is a solid film lubricant. It has been proven to increase heat transfer to the air at a rate of 10-15% over bare metal surfaces lowering operating temperatures.

Something to think about