What grit sandpaper to prep for paint???

[GUINNESS]

I'm eventually going to paint my engine cover, but I need to sand and prep the hell out of it since it's plastic. Does anyone know what grit sandpaper to use and how to prep it? I don't want to get something too rough that I end up destroying the cover, nor something too fine that it doesn't work.

Thanks.

[PersonaNonGrata]

I wonder if you even need to sand it. It might be enough to do a very thorough cleaning and degreasing. The plastic is a little textured so the paint should adhere to it so long as it's clean. Or maybe just a chemical paint prep.

[GUINNESS]

Majority of people I talked to said it can't be done cause the plastic is too soft. That's been disproven as I've seen pics of a painted cover on an S52 engine (the kind in my m3). I talked to the person and they said clean it, sand the hell out of it, prep it, paint, clear coat, done. So unfortunately, it's gonna need sanding. He said sanding and prepping were the important parts and I haven't been able to get him to reply what to use to sand and prep

[PersonaNonGrata]

Originally Posted by GUINNESS

Majority of people I talked to said it can't be done cause the plastic is too soft. That's been disproven as I've seen pics of a painted cover on an S52 engine (the kind in my m3). I talked to the person and they said clean it, sand the hell out of it, prep it, paint, clear coat, done. So unfortunately, it's gonna need sanding. He said sanding and prepping were the important parts and I haven't been able to get him to reply what to use to sand and prep

Okay, that sounds like the proper way to do it. I too have seen some painted plastic engine covers. One was in a 4.4 X5 and my friend who had a Volvo S60R had a bunch of stuff painted.

Maybe this info will help you.

[Thunder22]

From the corvette forum, people paint their fuel rail covers a lot on vettes:

If you want the paint to stick you will need to rough up the part and use an Adhesion Promoter...

Scuff-it Paint Prep Gel - $13 (an old tooth brush helps here too)
Bulldog Adhesion Promoter - $14 - Quart Use as a starting spray mist and or add to primer/base/clear --- It is also a flex agent to allow some twisting on plastic parts without delaminating.

[Thunder22]

here's another suggestion - (vette fuel rail covers are plastic btw)

Standard automotive paint will work just fine. No need for a high heat paint on any of the plastic pieces. The painter should use a flex agent on the fuel rail covers and the radiator cover. A good primer and then basecoate and clearcoat.

If you want a smooth finish on the pieces, you will need to smooth them out by sanding. Start with 220-grit paper to remove the texture. This will take some time to do so plan accordingly. Go to 400 grit or use a gray scotchbrite pad to smooth everything out. Get the automotive grade scotchbrite pads, not the ones at Home Depot.

Drain the coolant from the expansion tank by sucking out as much as possible with a turkey baster. There are two radiator hoses at the bottom of the tank and you may lose a bit of coolant as you remove the hoses. You can insert a plug in the hose ends or simply clamp the hoses shut or even just raise them up out of the way. Doing a checkered pattern on the tanks looks nice, but it does involve lots of masking on the part of the paint shop so you may wind up paying for extra labor.

The windshield washer tank has one wire for the pump and one wire for the liquid level, and the small hose going to the wipers. The pump and float can be removed for sanding, but because they are on the bottom of the tank, you won't need to sand down that far. Look at the tank befor removl so you get an idea of how much of it really needs to be sanded and painted.

Ask the painter to put a heavy wet coat of clear as the final clear coat. It wil help with depth and allow you to polish out scratches over time.

The fuel rail covers are touchy going back on as the left side (where the braided line goes thru the cover) will touch the line. Just put a strip of vinyl electrical tape on the edges when you replace the covers and pull it off after they clip into place. You may want to have the painter paint the indents for the letters and for the ribs. A contrasting color works nice with them. Same for the "Caution" on the radiator cover; white, bright red, or yellow on the letters.

[GUINNESS]

Thank you very much guys I'll probably start this project in a few weeks or so and will definitely post when all done. No need to see the process.