Polishing cylinder cooling fins

Ride

Active Member
On a painted motor does sanding and polishing the fin edges effect adhesion of paint on the flat surfaces?

I admit that while I did a good job degreasing I skimped a bit when it came to keying/scuff sanding every surface of the motor. Certainly between the fins was neglected.

I used a high temp 2k primer and top coat.

Anyone polish their fins and experience flaking later?
 

Tim

Administrator
Staff member
I've seen lots of people do this, especially with engines painted black. While I suppose at the molecular level having the edge of the paint exposed might result in flaking (esp with a less than great prep job) I think you'll have chips/flaking regardless over time if the prep work wasn't great.

Probably worth having the paint cure properly before sanding the fins.

This is why I leave my engines bare aluminum :)
 

Sonreir

Oregon
DTT SUPPORTER
I just used silver paint along the edges of the fins on mine.
 

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Ride

Active Member
Sonreir said:
I just used silver paint along the edges of the fins on mine.
Lmao that’s brilliant!
Is it true paint doesn’t need to be high temp on an engine? I thought I’d read that around the internets.
 

Sonreir

Oregon
DTT SUPPORTER
Ride said:
Lmao that’s brilliant!
Is it true paint doesn’t need to be high temp on an engine? I thought I’d read that around the internets.

The edges of the fins are cool enough that it doesn't matter. The black is high temp paint, everything else is Rustoleum.
 

jpmobius

where does this go?
DTT BOTM WINNER
I've never had any flaking issues, but I am pretty careful prepping the fins if I know I want the edges polished. I've used normal 2k urethane, but normal spray can engine paint seems to be just as good on cylinders. After cleaning completely, usually glass bead, but the key to having a really good job is to polish the fins before you paint. I take a hand file and flatten and dress all the fins I want polished so they are nice and even with each other and of comparably thickness. This does not take much time and really makes a big difference. I take a paint stir stick and some 220 wet or dry paper and scuff up the top and bottom of the fins along the outside edge to make sure there will be great adhesion there. I don't think you need to fuss a lot deep in between the fins. Then I sand the edges I want polished with #600 and clean everything up and paint. Having filed the fins previously lets you use a block with the sandpaper. Once the paint is dry, it is an easy job to simply sand again the edges with the #600 to take the paint off. You'll get really crisp, sharp contrast between the bare edges and the paint, and no flaking at all. If you want the edges shinier, you can polish without fear of damaging the paint, but I usually leave the #600 grit finish - it is easy to renew the look down the road by simply hitting it again with the sandpaper.
 

doc_rot

Oh the usual... I bowl, I drive around...
DTT SUPPORTER
DTT BOTM WINNER
Like JP I prefer to polish the fins before paint. That way you can't nick the paint when you are doing more of the aggressive shaping. After paint I wipe off the fins with acetone. Leaves a crisp line. Also if you are worried about adhesion and don't have access to media blasting you can use some metal etch prep. Just spray it on and hose it off, provides good "tooth"
 

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