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painting cylinders

When rebuilding air cooled bike engines it is common practice to paint the cylinder heads with a high heat paint. (usually in silver or black)

Why don't I ever see porsche rebuilders doing this?

Duplicolour high heat with ceramic is an excellent paint I have used on many bikes, including 2 stroke bike exhausts etc.

Any reasons why you wouldnt use this on porsche cylinders?

Kirk
Old 01-19-2006, 08:30 PM
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I do not know of any paints or coatings that can cost effectively transfer heat away from the material they are bonded to. That being said reducing temperatures in an air cooled porsche motor, especially in the valvetrain area and heads and cylinders pay dividends in long term durability and performance. Any coating will inhibit heat transfer from the heads to the atmosphere.

What is your reason for painting the heads, to make them look slick and keep them looking slick after the engine has been run for many hours and miles? If so I would pass on this. Unpainted surfaces make it easier to look for any leaks which may pop up in the future, or cracks for that matter. AFAIK one of the only heat transfer paints or coatings I have ever read about is the special paint that was used on the SR-71. Not only did it contain special "beads" to deflect radar but its color was closely guarded, it isnt black, its a dark blue/grey and for some reason it has the ability to disperse as much heat as it absorbs or comes into contact to, quite important when you are moving at mach 3+.

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Old 01-19-2006, 11:41 PM
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I don't see why you would want to. You really would have to crawal under the car to see them.
Cylinders are aluminum, old T jugs are cast iron maybe those could benifit from painting, but as said, adding barriers against optimum cooling....
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Old 01-20-2006, 03:13 AM
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There are coatings, TechLine sells them, that actually increase surface area with a the use of a crystalline formation. The theory is that increasing the area that cool air contacts will increase overall cooling. These products were produced to reduce radar signature, drag and heat that formed on the surface areas on the SR71 "Black Bird" spy planes. This coating (offered by TechLine) is black.
The formulas for these products became available through the "freedom of information act".

It seems unnatural to coat something in order too help it cool but it works.
That said, we used it on two race engines and saw no temperature reduction. It is important to state that we really had no way to measure cylinder temperature.
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Last edited by Henry Schmidt; 01-20-2006 at 05:38 AM..
Old 01-20-2006, 05:18 AM
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Air density has even more to do with cooling, thatís why the higher you go the hotter your engine runs even though the outside air temperature drops.
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Old 01-20-2006, 05:43 AM
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I powder coated my valve covers, but I suspect paint or any coating on the cylinders would reduce the ability to dissipate heat in two ways, any coating will act as a inhibitor for convective heat transfer, and the coating will decrease the volume area of heat transfer between the fins thus less mass of air to carry away heat.
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Old 01-20-2006, 08:20 AM
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I had a ceramic coat about .0012 inches of thermal barrier coating put on my piston domes to help reduce detonation in my high compression engine. I also used and believe in dry film lubricants for internal engine components.

Best Regards,

alex
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Old 01-20-2006, 08:56 PM
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I keep a can of the techline thermal dispersant coating on hand just in case I'm having a set of cast iron cylinders nikasil plated so that I can have my local autobody shop thin it and spray it on to the cylinders as thin as possible. More of a cosmetic fix than anything in my opinion. I did have a set of heads coated, along with cylinders and saw no measurable difference in monitored CHT/EGT with or without the coating back when we were doing lots of comparison testing between coatings/treatments and what they netted us.
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Old 01-21-2006, 05:10 AM
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BTW, Keep in mind that in the SR71 application, the heat is generated by the friction of the air against the airplane's skin, and so much as you can get this air to take heat away with it I guess that's a good think.

In the 911, the heat is generated by combustion within a space enclosed by the aluminum head and cylinders. If the heat is not conducted out through the metal, it really has no place else to go except out the exhaust with the spent gasses.
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Old 01-21-2006, 06:18 AM
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Quote:
Originally posted by Henry Schmidt
These products were produced to reduce radar signature, drag and heat that formed on the surface areas on the SR71 "Black Bird" spy planes.
...and the price per gallon is similar to what it costs to rebuild an entire engine, right....
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Old 01-21-2006, 07:07 PM
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Old 01-21-2006, 07:23 PM
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When using high heat ceramic paint on air cooled bike engines, there was three reasons:

1. Ceramic paints should help dissipate heat from the cylinder. Not much, but a little bit. In particular if you use flat black.
2. Because you aren't in there ever day, your cylinder fins will get coated with crap. Ceramic paints stop surface corrosion and do an excellent job of stopping dirt and liquids from sticking to your cylinders. (Which in my opinion will do more to stop heat build up and promote good cooling than anything else)
3. Its just looks nice.

I have also heard of cermic coatings being used on piston domes. (not $5 paint but special ceramic coatings)


I have been surprised by the number of porsche motor pictures I have seen, and no one seems to have touched their cylinders with anything but bead blasting.

(Or have I just missed alot of pictures?)

Thanx
Kirk
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Old 01-22-2006, 08:21 AM
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The biggest reason I see is that an aircooled motorcycle has to both cool when stationary (no air flow) and in motion (with air passing over the cylinders). Being that you have both convection and radiant cooling, most definately the thermal dispersant coatings (like those made by Techline) are a plus. Bead blasting / shot peening the cylinders increases the surface area and causes micro-turbulence, helping to get more heat out with the air forced over the cylinders by the cooling fan. Coating an aluminum cylinder would probably reduce cooling and surface area, at least in something with shrouded, ducted, forced air cooling.
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Old 01-22-2006, 08:36 AM
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The coating in question here would most commonly be called teflon or dry film....

Eric Hood
Old 01-23-2006, 08:05 PM
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What about the case?

I can see not coating the cylinders, but what about the case (especially the mag cases)? I have seen some nasty porosity (rusting for a better word) in mag wheels if you didn't keep them painted/clear coated.

tadd
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Old 01-24-2006, 06:30 PM
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Could the Nickies be black anodized? That seems like the best solution, but I think you can only anodize billet aluminum.
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Old 01-25-2006, 08:04 AM
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Well, Nickies are indeed billet and would be anodizable (I have anodized display pieces for non-functional use), but the problem I see is the need for selective plating. The nikasil process actually nikasils the whole cylinder, then we go back and shot peen blast media the outside to remove the excess plating where it's not desired, then finish machine them. Considering the excessively high thermal conductivity of our alloy (over double that of the factory mahle alloy used on 3.2 Carrera and later 993 & TT cylinders), I would think that black anodizing, other than looking pretty, would actually serve as a detriment and reduce surface area / turbulence that helps cooling. The money would be better spent thermal barrier coating the pistons and the chambers, as well as the exhaust ports, if trying to reduce head temperatures further.
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Old 01-25-2006, 08:25 AM
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Well, as long as we are on the topic of internal chamber coatings:

This is what they are advertised as doing:

Piston Coating
-----------------
Thermal Barrier Coating (For Top)
-reduces part temperature
-increases horsepower
-reduce fuel consumption
-reduce detention



Dry Film Lubricant (For Skirts)

-high pressure lubricant
-reduces friction and scuffing
-no clearance changes to compensate for coating

Since no one seems to like my idea of using high heat ceramic paint, or coating on the outside of the cylinder fins, Here is another method to keep heat down. (Costs about $45 cdn per cylinder)

I have never tried these types of coatings.

'Determined', How long has it been since you did your pistons? Have you seen any negative effects? Would you recommend it?

'tadd', I tend to agree with you. I used high heat silver on my transmission. Why doesnt anyone do their case?

Kirk
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Old 01-25-2006, 11:14 AM
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It is in my experience that the dry film lubricants do add a minimum thickess of .001" and in the case of Nickies, this must be taken into consideration since we're already running the pistons very tight and you run into situations where the piston won't even fit in the hole after being coated. I always specify to coat skirts minimum thickess possible. Same with these same coatings for use on bearings- you must double check your clearances after the coatings have been applied.
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Old 01-25-2006, 11:22 AM
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