Wednesday, May 4, 2011

Firewall

I've realized I can't put all the controls back into the cabin until I clean up the light rust on the firewall.

Also, all the Tinnerman nuts are rusted and some are broken.  Since they're riveted through the firewall it would be tough to get at them once the rudder pedals, etc. are in the way.  I've ordered new Tinnermans.  One thing I realized is Cessna used plated nut plates and all you can get today are primed.  I think I'll add some paint, probably silver, to give them a better chance against rusting.  I'd like to think I've learned form all the rusty steel parts I've been cleaning which were only primed. 

The Tinnerman nut strips (A6221-8Z-8-D) used on the edges of the firewall for attaching the cowl are no longer available.  I read a posting at the club site where the person carefully riveted new nut plates to the strips in places where the little spring tabs had died.  I'm just going to make new strips from aluminum and rivet the nut plates to them.  Using Matched hole construction, remember the Thorp T-18, I can make the new strips faster than fixing the old ones.

The other thing I expected to find at the club site was a good recommendation for painting or treating the firewall to stop the rust, no such luck.  The firewall is Ternplate, think steel coated with 90/10 lead/tin solder.  They don't make it anymore because of the lead thing and cancer.  It's what was used to make the gas tank on my WACO NINE, 83 pounds of steel, rivets, and soldered joints.  Originally I thought it was galvanized steel so I was going to clean it and lightly treat it with Corrosion-X.  Galvanized is coated with Zinc and resists rust even at minor scratches.  It has to do with the galvanic action of the Zinc.  Ternplate has no such galvanic action, scratch it and it rusts.  I suppose you could re-solder the affected areas. That sounds like to much work except where you need a ground strap attached. If I were doing a restoration I might replace the firewall, but I want to fly this thing before the grandkids turn into teenagers.  So, I'm going to lightly clean it up and paint it with some Rust-Oleum probably a high temp version.  I don't like the idea of painting a firewall in case of a fire.  They make a paint which can be used on exhaust pipes but it has to be cured at those high temps, not practical for a firewall.

1 comment:

  1. Aluthane came to mind but it has a lot of solvents. I used some on my struts until I can get the proper paint on and it kinda matches. The fire issue is something to consider though so I am not going to put in on the 140 fire wall. I can hardly get to the fire wall but did remove the engine and clean it up quite a bit with stoddard like solvent, the real stuff. Had some oil on it too a little.

    I do not know if you know about Aluthane but it can be used as a primer and sucks out moisture in drying has a corrosion proofing effect. Gotta get my 6221-8Z-8D made up too. I did see one on ebay or somewhere for 10 bucks but did not buy it at the time. Like you say faster just to make them.

    Here is a link to info on Aluthane if you do not already know about it. I am not trying to sell this product just putting the link for info only.
    David

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