Best method for painting barrels silver?

Gents,

I plan to strip the top end of my '74 850 this winter and want to repaint the barrels whilst its down. I want to keep them silver, as I prefer the look.

Since rebuilding it, it suffers from 'Yellowing' of the barrels. This is despite using 'off the shelf' paints that have been successful in the past. As discussed previously on here, it seems that modern paints just ain't what they used to be.

Naturally, due to barrels being a PITA to remove, I want the most durable finish I can get.

Generally, I am pretty much 'anti powder coating' but it is tough stuff, and the heat tests done by Comnoz seem to show there is zero issue with regards to heat dissipation.

So, I am leaning towards powder coating. Can anyone who has recently painted barrels silver please give their experience as to either what has worked well, or what to avoid?

The last time I painted the barrels on my '73 I used Dupli-Color Engine Enamel "DE 1615 Aluminum". Label claims it's good to 500 degrees F. Did the entire engine with it and it holds up fine. I've done it this way since new.

Silver rattle-can Rust-O-Leum. You'll never have to paint them again, and they'll never rust as long as you prep them reasonably well and let dry thoroughly before spraying. 2 coats.

I had my barrels powder coated silver. Not sure what type of coating it was but it never went hard and flaked off. I resprayed over it with PJ1 in gloss black. I don't know if they do PJ1 in silver but B&Q do Rust-o-leum in silver for BBQs and it's good stuff.

Powder coating relies on electrostatic attraction for the powder to adhere to the surface to be coated. It is a near physical impossibility to achieve a uniform electrostatic field on a surface having fins. The fins act like the poles of a magnet that are repelling each other. The result is a thick deposition of powder in one place, and a near zero deposition in another place. The overall effect is non uniform thickness of powder that is not attractive, or optimal from a heat transfer standpoint.

I would strongly recommend using paint, rather than powder.

Slick

A friend had the cast iron cylinders on his `67 BMW R60/2 powder coated black. They turned out great. There does seem to be a loss of surface detail as the powder coat is a thicker and smooths out the casting marks. Almost as if they were dipped in black paint.
Contrary to popular folklore, he doesn't to seem have any problems with the bike running too hot.
Finding a silver powder that has the correct finish might be the hard part but I'm sure they have a "satin" finish that would look good.

Ive preferred VHT SP127 Univ. Aluminum, Its never yellowed, I have used on all my Honda-4 rebuilds, nice bright silver. If you do paint, do not use a engine clear coat, I did that on one of my engine and it yellowed. I used VHT clear, there may be other clears available that wont yellow.

FE. I used VHT 550F aluminum on my barrels, head and cases. It bubbled a little on the head in the exhaust fin area below the rocker shafts but has settled down nicely and appears to have cured. It hasn't yellowed and sticks well to the cases also. The issue you may have is getting the barrels clean enough. I didn't blast mine and some signs of rust are coming thru'. I'm sure you will do it properly. I don't as all my paintwork are 10 ft jobs!

mschmitz57 said:

A friend had the cast iron cylinders on his `67 BMW R60/2 powder coated black. They turned out great. There does seem to be a loss of surface detail as the powder coat is a thicker and smooths out the casting marks. Almost as if they were dipped in black paint.

Click to expand...

The loss of surface detail mentioned here is due to thick powder. Not only does the thickness reduce conductive heat transfer, but the loss of surface roughness reduces convective heat transfer, especially at low air speeds when you need it the most.

While nicely polished fins may look cool (hip-speak), a sand cast texture actually runs cooler (thermodynamic speak).

Slick

Be sure not to use paint intended exhaust parts i.e. headers, I believe they don't allow heat transfer.