Steps to prep model A engine before painting

J

JD4430

Member
My engine block has a lot of surface rust and grease and oil. I was first planning to give it a good wire wheel brushing to remove access rust. Then I would thoroughly clean it with a degreaser. After that I was planning to spray on a rust treatment that uses Phosphoric acid, let it soak for a while then rinse and dry thoroughly. I assume I still need to spray on a primer. So my question is what kind of primer do I use? I have read some posts suggesting that a primer isn't even used.
 
Just wipe the block down, I use acetone. The rattle can paint is OK, I prefer the brush on.
This leaves a smooth glossy finish.
 
Your approach is correct. Use a rattle can self-etch primer on your scrubbed base after getting creative with tape and aluminum foil (works great for masking & protecting.)
 
The rust on a block is usually heavy.
You could try the spray on Evaporust gel, after a good clean.
Put cling wrap over the top.
Rust should be gone in a day or two.
Clean well before painting as it seems to be slippery stuff.
 
After you have done all the prep described above and painted the engine with the rattle can, let it dry for a couple of days. To prevent corrosion in the head gasket area, take a rag around your forefinger and seal the edge of the head gasket with wheel bearing grease. Wipe off the excess. The head gasket can weep and start corrosion on your newly painted engine. I repeat this once a year and my engine paint job looks as good as the day I painted it. Ed
 
I dry scrape what I can, then use tons of commercial grade oven cleaner (the kind with lye) and several sizes of wire brush. Thoroughly rinse with a hose after each coat of cleaner. I’ve had a couple of engines need a third coat in some places, but two is sufficient with most. After the oven cleaner and rinse you may have a bit of flash rust (that actually proves you got through the grease). I use brake cleaner and a coarse rag to finish, then paint. I use Bill Hersch Ford Engine Green with a brush, no primer. It’s a bit dark and glossy for my liking, but it’s what I’ve always used and I know separately painted parts like water pumps and goosenecks will match.

Oven cleaner also works well on the block interior and the underside of the cylinder head, but I keep it away from the babbett as I’ve heard (no experience) that it can dissolve babbett.
 
Warm it up and spray on some oven cleaner. It'll get the grease and old paint off leaving it ready for paint after you've rinsed it and let it dry.
 
I follow and use KBS Motor Coater system. They even have Ford engine green. They're an Australian company, and I don't know if they sell in the USA though. If you look at their website, it gives you the preparation procedures, which you can follow, and just use your own readily available products.
 
Bob Bidonde said:
Every layer of paint impedes heat transfer via radiation & convection, so skip the primer.
Click to expand...

Jus' playin' Devil's advocate with you Bob, but someone can argue that most Model-A engines need to retain what heat they do make for more efficient combustion, so excessive paint build-up might be a positive thing.


Things have changed regarding what is "best". If the cast iron surface has been thoroughly cleaned and pickled with the Phosphoric, likely there is not much need for a self-etching primer because the texture & porosity of the cast iron. IMHO the best product to use as the foundation is a very light coating of catalyzed Epoxy that is just barely thick enough to have coverage. Good quality Epoxy is very, very durable, ...and it adheres to almost anything.

Then, if you look at original factory photographs of Model-A engines, you will see where the Engine Green paint was applied very thinly prior to assembly. To replicate this today, you can use as little as a ½-pint of catalyzed Engine Green that has been 'over-thinned' and very lightly applied with a foam brush. Apply this topcoat after the Epoxy has dried but within the recoat window of the Epoxy. This will still show the texture and casting imperfections yet between the catalyzed Epoxy and Urethane topcoat, it will seal the metal from any future rust and be very chip resistant and durable for years simply because of the very little mil thickness.
 
After much scrubbing, I've used Brent's suggestion as well to prime with catalyzed epoxy using a brush. Consider epoxy primer as a 'glue' to grab tight to the base and hold the top coat. Only works during the epoxy's 'window' before curing completely.

If you are painting an engine in pieces, brush a 1/4" in under the head and in on the block deck. This has been very successful in holding back creeping rust, especially over the vin pad area.
 
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