6BTA cast iron primer – zinc rich, zinc chromate or etching?

[Alex]

Hi, Getting ready to pickup a block and head from the machine shop and start reassembly.

I would like to get a coat of primer on the bare cast iron before assembly, thinking of masking and priming all parts, assemble and then shoot the topcoat, when its all together.

Regardless of the sequence… What is the best type of primer to go against the cast iron?

I can spray or brush 97% zinc rich primer (cold galvanizing type), zinc chromate rattle can (the green or yellow stuff) or spray a wash etching primer.

What is commonly used and what provides the best protection on engine blocks?

 

Thanks

Topic

[Alex]

Tony,  I agree on keeping the engine room and bilges dry. May put in a dry bilge pump when the time comes to get the last drops out.

Question on “always have an oil pan heater or something equal.. Maybe 200 watts min.  per engine/ per 500 cu ft of engine room volume “

Would a oil pan heater be beneficial in the tropics where temperatures are always above 70F?

In this case maybe and oil pan heater is not needed but an engine room dehumidifier is more in line with drying the air/removing moisture/condensation.

Let us know.

[Alex]

Primed block last night, 6bt storm block

I’ll continue to post as I slowly build this one up, trying to limit  my posts on the painting aspect for this thread.

 

1 user thanked author for this post.

Scotth

[Rob Schepis]

You did your homework and made a plan.  Yes, lots of work but it will help you sleep better and should pay off in the years ahead.  Thanks for posting the details.  Pics would be great too.

[Alex]

Thanks Tony, did some research as suggested and there are multiple opinions.

Some of these are:

-Etching or chromate primers will add no benefit on a cast iron surfaces as the acid it contains would not react with cast iron. Better suited for non ferrous metals.

-Zinc rich primers are better on cast iron due to the zinc component.

-Epoxy primers are good but may need scuffing afterwards for proper topcoat adhesion.

-There is no need for a high heat specialty paint vs you need a high heat paint.

-Some use rusty metal primer from Rustoleum and then any brush-on gloss enamel.

-Others spray the primer of their preference and spray two part polyurethane.

-Some argue that primer is not needed as most manufacturers don’t prime engines when new anyways.

I decided to use zinc rich primer thinned with lacquer thinner for the cast iron block, head and coolant bypass piece. Then a etching primer on the alum oil pan, valve covers, timing housing (pending). After blasting all the steel brackets, parts and fuel lines, I treated them with phosphoric acid, so they are good to topcoat without re-priming. 

For top coat I’ll spray a two part polyurethane when I get the engine sealed up, then Ill attach all the prepainted accessories, (aftercooler, heat ex, starter, ex manifold, turbo, pump etc).

Anyway you put it, its lots of work.

 

1 user thanked author for this post.

Scotth

[Tony Athens]

I think your best answer to this will come from a google search that is not specific to boats.. Automobile , antique engine,  and machinery guys have the same questions.. Lots of different methods out there.

But IMO,  the best long term method in a boats engine room  is maintenance and keeping it dry an warm.. Never park a boat with saltwater in the bilge , or in the engine saltwater cooling system) ,  and always have an oil pan heater or something equal.. Maybe 200 watts min.  per engine/ per 500 cu ft of engine room volume 

[Author]

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