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I had problems getting my header tank to fit properly on the forward deck. On the sides (the 13" dimension) the flanges were not flush with the deck. The flange was basically "rolled" off the header tank so that even if it fit properly, it would make contact with the fwd deck only on one thin line. Also, the fore-and-aft faces were farther apart than the honeycomb insert on the forward deck, leaving a LOT of overhang between the forward-and-aft flanges and the deck, at least in the center where the forward deck is the thinnest (measured fore/aft).
This description of the problem is weak, but if you've fit your header tank against the deck, you probably know what I mean. Bill Harrelson apparently cut off his flange and built a new one. Orin Riddell suggested I cut out the honeycomb on the deck where the flange sits, cover with 2-BID, and proceed with only glass-to-glass bonds. Doug Weeldreyer (sp?) suggested I build up the gaps with micro and cover with 2-BID, then proceed. All of these methods should work, but I did something else.
First, I made the tank slightly thinner by pushing the aft face towards the forward face and using the slosh baffles to retain the tank in this condition. The end result had a tank flange bowed in on the aft face (just like the forward deck) and a forward face that was no longer bowed out in the middle (thus conforming to the shape of the deck). While still not a perfect fit, it was much better. The plywood pieces left over from the braces bondoed onto the top of the deck were used to make a jig for this.
I then built up the gap between the deck and the flange with flox. This was done in sections, one flange at a time. For each operation I covered the tank flange with 4 mil plastic double-sticky taped to the flange. (Any release tape method should work.) I then gooped a lot of flox into the gap area and plunked the tank onto it, put two 25 pound shot bags on the tank, and let cure. After cure, I ground off the excess flox, leaving only that below the flange. The end result was what we called a "flox gasket".
The best tool to grind off the large amount of excess flox was a drum sander on an electric hand drill. Strongly recommend you have a helper follow you with a vacuum cleaner to clean up the dust as it is produced, else your whole shop will turn white in no time at all. Total grinding time was about 45 minutes combined to remove about a third of a pound of flox (estimated). Total time to make the "flox gasket" was about six hours, in several sessions.
I have become convinced thru this operation that simply gooping flox down and plunking the tank on it will result in a less-than-perfect bond. We saw many areas with voids, and a lot of squeezeout on the inside. By doing this operation in stages, you have an opportunity to smooth out and repair imperfections in the flox bondline.
When complete, the tank just plunked down solidly into position, neat as you please! This made the final floxing into place a much less harried operation. I'm not sure in retrospect that it is any easier than the other methods described, but it worked well.
For those interested, the total time spent on the tank (prepping, installing fittings and baffles, mounting to forward deck) was 55 hours.
- Rob Wolf
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
Builders' Bookstore: http://www.buildersbooks.com/lancair
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