UPDATED 5/4/16 - Here's a very popular mod for giving your engine bay a period-correct look while providing a functional way to fill your cooling system and to allow for expansion. Back when I did this mod originally (2012), these tanks were available on E-bay for around $30 - $50. They were typically found on big-block Ford sedans back in the day and should still be plentiful out there at swap meets and such.
Quite a few members contacted me asking for more information on the process of modifying and installing a vintage (early '60s) Ford degas tank on a smallblock, so I thought I'd write this up for those contemplating this idea. I started with a couple of tanks bought on ebay a couple years ago for $30 - 35 each, figuring I'd ruin one in the process. After noodling this idea over for a couple of years and looking at many other versions of this mod, I came up with the following. After pressure testing both tanks, I started with the one that only had a small pin-hole in an existing soldered seam that was easily repaired - much to my surprise the mod ended-up being so easy that the second tank stayed on the shelf for use as a spare someday.
1) Note that the bigblock degas tank thermostat housing mounting holes are off by ninety degrees, requiring the removal of that part or an adapter for the smallblock thermostat housing. I chose to remove the housing and most of the tube from the degas tank. This is done first by drilling out the pressed-over bracket metal in the thermostat housing holes to free it from the tank bracket, then by cutting the 1 1/2" tube approximately 2" from the bottom of the tank. Pictures of a modified and OEM tank for a "before and after" view:
2) After mocking it up with a piece of thick cardboard, I fabricated an adapter bracket out of some 3/16" thick aluminum scrap that I had laying around to mount the tank to two of the top waterpump bolts using one of the original brackets on the tank. The adapter bracket covers the two original holes in the tank's original bracket - the other upper hole in the adapter was used to mark a spot on the original tank bracket so it could be drilled and the forth hole - the other lower hole, is just through the adapter bracket and is the lowest hole on that part. This mounting worked well from a hood clearance standpoint, but puts the tank very close to the distributor. If you're using a large head / cap distributor, you may need to move the tank to the forward point on the waterpump. To facilitate this mounting location, I used two longer bolts for those positions on the waterpump, but had to thread the bolts a bit higher up the shank as the majority of the bolt shank is not threaded, so that the bolts would fully seat in the water pump and timing cover and leave enough threads protruding out the back of the engine front cover to act as a mounting point. Pictures of mounted tank and of the mounting bolts - note that these photos were at the mock-up stage so the bolts holding the tank to the adapter bracket were only temporary - the permanent ones are sized appropriately.
3) I made a bead tool using instructions found on-line so that I could put a raised bead in both the stub of tubing on the bottom of the tank and at each end of the two 1 1/2" aluminum tubes that are used to piece together the upper radiator hose and the hose that spans from the lower tank to the thermostat housing. Pictures of tubes with beads (see bead on lower tank tube in pictures above) and bead making tool - 10" vice grip with woodruff key and 1 1/2" carriage for a muffler clamp welded to jaws.
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