Painting my engine Harley Sportster & Buell Discuss Painting my engine in the Motorcycles forums; Need some info..Going to paint my cylinders and heads on my 89 1200 xlh this winter. Need to know if it is a must to leave the edges of the ...

[wekelm]

Need some info..Going to paint my cylinders and heads on my 89 1200 xlh this winter. Need to know if it is a must to leave the edges of the fins unpanted? My plan is to put a coat of red then mask off the edges and put a coat of black. The idea is to make the cylinders look sort of pin stripped. I'm wondering if this will cause over heating. I am running an oil cooler to help with the real hot days we ahave at times.

[frisco-rigid]

Hey Bill

I thought someone mighta had some First-Hand info for you but I guess not..

I would not do any of it myself but if you do it, definately let us know how it comes out..

I suppose you're going to use that High-Heat Header or B-B-Q spray paint,, yes.??

I don't see any reason to worry about the edges cuz it's the whole fin that dissapates heat..

Since you also run an oil cooler I don't think the heat retention will be That affected.. Just guessing though..

[Majicbringer]

You can paint the edges, it's not going to effect it that much. It's going to run a tiny bit hotter with thepaint on, but nothing that's detrimental. Many like to leave the edges unpainted to get that look you described. I'd have my motor sent out to do it, to Sumax's painting house, as those guys know their stuff. If possible, use poweder coating, you'll get a better bond and more durable paint. Sears sells a nice powder coating setup for about $150! If you have a wife see might wonder what your motor is doing in her oven, though...

Vincent motors were painted black top to bottom and look how those things ran!

[Wrightturn]

Hey Wek,

Haven`t said anything since I just don`t know. I have never painted cylinders anything but black. I used Harley or PJ1 paint. The engine will run hotter but I don`t know how much. My FXDX has the black wrinkle finish and has held up well. I use Mothers Back to Black and it still looks new.

There are coatings and paint which are supposed to improve heat transfer. I have read a little about them but haven`t found a use for them. What I believe: rough, sandblast finish will run cooler than polished, polished will run cooler than coated or painted.

My 1952 Vincent Rapide was painted to Black Shadow spec. It was done before I bought the bike around 1972. The paint was a baked on stove enamel applied and baked in Richmond Va. It still looks great although it devalues the bike because it isn`t "correct". The Vincent ran cooler than a Harley for a lot of reasons that I won`t bore you with. I just told people it was racing paint.

[MONTY]

You'd need some fairly fancy instrumentation and a carefully designed and conducted experiment to reliably measure the temperature difference made by painting the cylinders and heads of any given air-cooled engine, it really isn't that much of a big deal (any home-done, ad hoc experiment is more likely to show DT from differing running conditions / duty on the motor generating the heat in the first place!).

As for the difference between all painted or fin-edges revealed, i would doubt anyone short of HD themselves (and maybe bigger aftermarket folks like S&S) would have the means to measure the DT, it's just too small a difference and would likely be lost in the noise.

But the biggest clue is that HD paint the barrels and heads on some of their motors (both XL and BT), with and without revealed fin-edges, so it clearly isn't a problem. Your only real issue is getting the right paint and applying it correctly so that it stays on ... !

p.s. As aluded to in other posts, two points:
1. Some paints actually improve the emissivity of the metal surface if they are applied properly, so you'd actually run a little cooler.
2. By far the biggest issue is suface area - "rough" surfaces have a lot more area than smooth/polished areas; cutting back the fins will make a really significant reduction to cooling, and increasing fin area (as S&S have done on their Evo BT style motors) will let you run significantly cooler.

[Joyride]

I painted my cylinders about 5+ years ago and it's held up nicely thus far. No issues whatsoever with heat dissipation. It is a rattle can high-heat engine paint (kind of gloss finish) I picked up from Autozone and painted in my driveway in the frame. It just needs touch ups here and there.

[street bob]

Looks good. Give us a full picture of that scoot!

[Joyride]

Originally Posted by street bob

Looks good. Give us a full picture of that scoot!