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VW Conversion
To All:
I've uploaded some of the HVX drawings & photos to my blog. (bobhooversblog.blogspot.com) -R.S.Hoover |
#2
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VW Conversion
On Fri, 01 Jun 2007 20:56:46 -0700, "
wrote: To All: I've uploaded some of the HVX drawings & photos to my blog. (bobhooversblog.blogspot.com) -R.S.Hoover Bob when you do a conversion what do you do to get all the oxide off the crankcase? the case I'm looking at converting is oxided a dark grey. I'd like to get it all clean again before painting it. ...without stuffing it up. Stealth Pilot |
#3
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VW Conversion
On Jun 2, 7:42 am, Stealth Pilot
wrote: when you do a conversion what do you do to get all the oxide off the crankcase? ---------------------------------------------------------------------------- Trick question, right? (Most conversions begin with a new crankcase. No corrosion.) -------------------------------------------------------------------------- the case I'm looking at converting is oxided a dark grey. I'd like to get it all clean again before painting it. ...without stuffing it up. --------------------------------------------------------------------------- Dark gray may not be bad. (It depends on the corroding elements.) A good de-greasing followed by a good scrubbing with a detergent having a neural pH, followed by a boiling-water rinse, may be all you need before painting. A wash with dilute phosphoric acid, ideally with chromate extenders, will brighten the surface. It produces a black phosphate residue in doing so that must be removed. You won't see the black stuff if you scrub-on the phosphoric with a paint brush cut down to make the bristles stiffer, but it will show up if you just allow the thing to sit. But if there is any corrosion due to salts you'll probably have to boil the case to get rid of the salt before you can address the corrosion. Worse-Case: (Old, salvaged bus engine.) Degrease, wash, then blast with crushed walnut shells. There are commercial products available specifically for prepping magnesium alloys. Some customers include the surface-prep & finish specs in their order. But some of that stuff costs the earth and I frankly haven't seen much difference compared to the methods I use. I'm not a chemist but the dividing line would seem to be between simple oxidation of the surface, which does not alter its heat-flow properties and which may be painted without further prep, and destructive corrosion that etches the parent metal and produces various crusty-looking residues that act as thermal insulators. Removing the SYMPTOMS of such corrosion does not address the cause and painting over the apparently clean surface ensures the corrosion will re-appear. I know that sounds sorta wishy-washy but there is some overlap between the types of 'corrosion.' On old/used crankcases I usually do a few tests before deciding which surface-prep procedure to follow. Since paint itself acts as an insulator, use the thinnest coat possible. And NEVER use any 'high temperature' paint, such as that advertised for wood stoves, barbeques, exhaust pipes or what-have- you. Such paints get their hi-temp qualities from clays or metallic salts and are excellent thermal insulators. -R.S.Hoover PS -- A boat yard can usually point you toward products containing phosphoric acid meant to prep non-ferrous alloys for paint. Ditto for a good paint store that deals with aluminum siding and window screens. |
#4
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VW Conversion
On Sat, 02 Jun 2007 09:26:40 -0700, "
wrote: On Jun 2, 7:42 am, Stealth Pilot wrote: when you do a conversion what do you do to get all the oxide off the crankcase? ---------------------------------------------------------------------------- Trick question, right? (Most conversions begin with a new crankcase. No corrosion.) -------------------------------------------------------------------------- appreciate the details bob. sorta what I thought. no trick question. the engine is a 1600vw intended for a non aerobatic open cockpit druine turbulent. it comes out of a vw varian. I'll be using something like ian peacock's PFA conversion details. 1600 is enough power for the turbulent. there is a 20 year history of using these engines in turbulents in england. I've been dithering for weeks whether I'd bolt the halves back together, tape up all the port faces and lightly bead blast the outer faces of the block. The paint I'm going to use is tempo aircraft engine enamel in the rattle cans. stop thinking. just get on and do it. Stealth Pilot Australia |
#5
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VW Conversion
On Jun 3, 3:36 am, Stealth Pilot
wrote: I've been dithering for weeks whether I'd bolt the halves back together, tape up all the port faces and lightly bead blast the outer faces of the block. ----------------------------------------------------------------- I've had mixed results using beads -- glass and phenolic -- on magnesium, in that specs of corrosion would appear after six months or so. With walnut shells, I've had engines come back through the shop after many years with the original paint intact. ------------------------------------------------------------------ The paint I'm going to use is tempo aircraft engine enamel in the rattle cans. ----------------------------------------------------------------- Probably over-kill. See if you can find a junked VW crankcase -- real junk; totally unusable. Clean small areas using different methods; paint with different paints. Keep good notes. Throw it out back of the shop where the weather can get at it. Check it every now & then, and update your notes. (Ditto for steel, WOOD(!), fibergals, aluminum and so forth.) I think you'll be surprised at how well some of the traditional methods/finishes hold up. -R.S.Hoover |
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