Midnight Special cooling fin clean up

[Michael March]

Just bought an '81 midnight special and I'm trying to clean it up. The cooling fins on the jugs have chipped black paint on them. Is there any fix for this? I searched the archives and have found nothing. This is seriously hurting the look of my flame thrower. I was thinking of maybe dremeling the paint off completely and then trying some heat paint. Has anyone tried this? Any suggestions appreciated.

[pathfinder]

I have not done this as my motor is not painted but I would just remove as much of the loose paint as possible with a wire brush on a dremal or by hand. Mask off what you can, then paint with VHT brand High Heat Paint or the wrinkle finish paint that HD sells. Then sand or scrape off the paint from the edge of the fins. Just my 2 cents.

[uk1.1s]

Black fins

I tried the DIY coating quite a few years ago now, hand removed the old paint I could, cleaned it all up and used VHT (very high temperature?) paint from an aerosol (Trade name was PJ1 it think and it was a US product).

Results were OK, but my shortcomings in preparation showed through after a year or two with some small loss of paint here and there again.

I quite liked the idea of polished ends to the fins which I've seen on some bikes. When I tried this I couldn't get a good edge, removing the paint with fine abrasive paper tended to leave a chipped edge, rather than the sharp line wanted. I guessed that my home DIY technique was poor and the coating a little bit brittle for this, so I made good with another few coats and left it all black.

Think If I was going to try it again ('cause the condition it's in now I can live with) I would do it with the head and barrells off and maybe send 'em to a professional coating shop.

[Bubba1954]

Actually a Black coated engine runs considerably hotter then the natural aluminum versions. This over time might lead to quicker ware charactoristics and sooner parts failures as the oil breaks down sooner under more heat. Its a know fact of physics that Black only absorbs and retains heat. Lighter colors like White or Silver disipate and draw out heat from whatever they coat.

This is why exhast headers on cars and trucks are usually white or silver to disperse the heat from within. This can add years to them also.

The Midnight engine color has always been a simple marketing sceem to make a bike look more special and unique. They have sold many over the years and still do today. Yamaha just released a Midnight version of the Warrior Roadstar.

Just food for thought...

[Dennyz]

I painted my engine 50K miles ago with PJ1 engine and case paint (satin). It has held up well for me. The trick is getting the surface totaly clean. I used a file to remove the paint on the fins, which also turned out well.

I just recently touched up some places that the paint had been chipped or worn off. The touched up area is undetectable.

Anyone painting their exhaust system black should try the new Krylon BBQ and Stove paint. Dries fast (15 min.) a rich dark satin black. After a 740 mile day in 90+ deg. temps at 75+ MPH, the header still has the dark smooth color (did not turn a chalky gray).

[Renegade]

Originally posted by Bubba1954
Its a know fact of physics that Black only absorbs and retains heat. Lighter colors like White or Silver disipate and draw out heat from whatever they coat

I don't think that different colors make enough difference to worry about. The color is simply a decorative choice. Look at the total amount of heat produced by an engine. The tiny differences in the efficiency of one color vs another when it comes to heat dissipation will have very little effect on the engine temperature. The ambient air temperature will have a greater effect on cooling efficiency than the color of the paint will. Unless you are building a competition engine that is pushing the absolute limits and every little edge counts, use whatever color paint that you wish because you will never feel the tiny performance difference it makes on a street engine.

Besides, how many people are concerned about the amount of heat radiated from the exhaust pipes that is blowing across their engine? Yet you rarely see anyone using header wrap on their motorcycle exhausts.

[Underdog]

Originally posted by Bubba1954
Actually a Black coated engine runs considerably hotter then the natural aluminum versions. This over time might lead to quicker ware charactoristics and sooner parts failures as the oil breaks down sooner under more heat. Its a know fact of physics that Black only absorbs and retains heat. Lighter colors like White or Silver disipate and draw out heat from whatever they coat.

This is why exhast headers on cars and trucks are usually white or silver to disperse the heat from within. This can add years to them also.

The Midnight engine color has always been a simple marketing sceem to make a bike look more special and unique. They have sold many over the years and still do today. Yamaha just released a Midnight version of the Warrior Roadstar.

Just food for thought...

This is not true at all. Why else would auto radiators (designed to "radiate" heat be painted flat black? Same goes for A/C condensers and all modern auto engines are painted black.

Back to the question. I cleaned the loose stuff off mine with a wire brush. I found that one from the plumbing supply store made to clean the inside of copper pipe fittings worked pretty good. Get some wax & grease remover from an auto paint supplier, put in a spray bottle and really rinse the engine down with it. I used Krylon BBQ black paint and it's still holding after over 1000 mile. VHT would work as well I suppose. The crinkle finish was only used on the valve cover. If it's not real bad just spray over it too and the crinkle effect will still be there. I hit the edges of the fins and the highlights on the VC with 150 grit after the paint dried. I finished up by spraying with S-100 engine brightener from the Harley shop & it lools like new.

[uk1.1s]

The physics of colour.

Don't agree with the comments on black "holding heat". Seems to go against all I've learnt on heat transfer..... and I have worked with some pretty well qualified physics graduates.

Agree that it adsorbs better than white. This is because the black pigment will absorb more radiation frequencies than other colours (including all from the visible spectrum...which is why it's black as nothing gets reflected back to you to see).

Anyway - just my "2 and 6" worth....

As "Renegade" says - the difference in radiation is minimal really for an engine like the XS11. As the Midnight and my Euro "Sport" has an oil radiator we haven't really got anything to worry about eh?

[nashville_bill]

It seems to me that electronics heat sinks are black, aren't they?

[Bubba1954]

Sorry to cause such a ruckas with my comments about the relationship of Black coatings and heat retention. Your responces have been fun to read.

It would be interesting to cunduct a digital cylinder head temp test using two identicle bikes riden side by side over the same 100-mile cource. One bike with a factory black coated engine and the other bike uncoated.

Maybe I should submit this test to Myth Busters on the Discovery Channel? <smile>

I personally love the looks of Black and chrome when used together. But unless I'm convined otherwise, I'm not sure I am ready to own a bike with a black coated air cooled engine.

Water cooled engines cool from within using the cooling fluid flowing through the ducts to transfer this heat to the radiator where it is cooled.

[Renegade]

Originally posted by nashville_bill
It seems to me that electronics heat sinks are black, aren't they?

Not always. I have seen several different colors... red, green, blue, gold, silver, and black. That does bring up an interesting point though. These heat sinks are anodised. Anodising works by creating an oxide layer on the aluminum, which is then dyed to get the various colors. And we all know that an oxide layer impedes heat transfer. Kinda makes you wonder, doesn't it?