Priming my engine for paint

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7/12/2017 3:56 PM

Restoring an 88 RM250 and had the engine soda blasted to bare metal. Today I sprayed some Rustoleum self etching primer on the engine before using the VHT Engine Enamel paint. The primer looks kind of "soft" to me after about an hour. I don't know whether that's due to it not being fully cured yet or not. I can easily run a finger nail through to the bare metal.

Will this cure to a more scratch resistant finish after a few days? I'm hoping I didn't make a mistake using this primer but the blaster recommended it be done before the paint was applied.



7/12/2017 4:34 PM

Here's a pic of the engine after priming.Photo


7/12/2017 7:47 PM

It really depends on how thick you put it on and how many coats you used. An hour isn't very long, I wouldn't expect it to be dry at that point, it will take at least a few days to fully cure. A rule of thumb I was taught is if you can still smell the paint, it's still gassing out and not completely dry. Did you use a self etching primer? These are meant to bond to the metal, providing a better hold than regular primer.


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7/13/2017 5:59 AM

Set it in the sun

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7/13/2017 7:22 AM
Edited Date/Time: 7/13/2017 7:34 AM

Read the directions on the primer can.......did you allow for flash time in between coats? There should be a stated time that the top coat can be applied over the primer w/out additional sanding.....for,proper adhesion..if you wait to long, you will have to lightly scuff the primer....not sure if your engine is completed, but a suggestion for a more professional look: paint as many parts as you can disassembled, clutch & ignition covers, head & cylinder ect. Then reassemble with new gaskets....the new gaskets will show & not be will look also don't want overspray on screws, nuts ect...


7/13/2017 2:53 PM

sandman, I just primed the engine and did not paint it yet. I assembled it as I figured it would be easier to prime and paint. I was able to block off the openings better assembled and used the old hardware to paint over (I bought all new screws and bolts for reassembly).

This Rustoleum Self Etching Primer isn't going to work I believe. It's still kind of soft and easily scratched even today - 24 hours after. I may strip it off and use the VHT type high temperature primer as that's the paint brand I'll be using. Then again, I may just say to hell with it and get it powder coated!

I hate wasting time! That primer sucks even following the directions to the t.


7/14/2017 12:07 AM

While I would ordinarily say primer before paint is best. (I like to use self etching primers as well) I found with the PJ1 or VHT engine paint it seems to actually stick best without primer. That said, I have had good luck with Shirwin williams self etching primer as well as Pro form self etching primer when I do use it. I usually go very light. One or two light coats. It will suck getting the old stuff off. I would use lots of good paper wipes with some lacquer thinner and an old paint brush to dissolve and wipe that uncured paint away. Good luck.