How to clean up melted aluminum piston from an iron cylinder

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How to clean up melted aluminum piston from an iron cylinder

Post by noiseguy »

Thanks to Pygmaelion for this one. The baking soda is a critical step; it neutralizes the acid for disposal. Also, this only works on steel/iron cylinders; it will (obviously?) melt aluminum jugs.
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I got back from Taiwan on Saturday, and inspired by the sheer volume of scooter goodness going on there, got down into the basement to work on my SB50p.

I had smeared a little piston inside the cylinder, so I put it in a heavy duty garbage bag. I took a plastic (not metal) 2.5 gallon pail, and filled it with tap water. I placed the garbage bag with cylinder into the water (keeping the top of the bag open, above the top of the pail) and poured in a third of a litre of muratic acid.

At the time, I was wearing a beat up coat, some jeans that I didn't care about, and an old paintball mask (because I don't have normal goggles... besides, it covers the full face). I had a big box of Arm & Hammer baking soda on hand, just in case.

As fair warning, you'll want to open all the windows, turn on some fans, and maybe even wear a rebreather. It took me one light whiff of this nasty jazz and I d... near fell over.

Anyhow, after checking to make sure the exhaust studs weren't going to melt, I left the whole thing to soak while I prepared the new pison/rings/wristpins/clamps. After 20 minutes of sinister gurgling from the bag, I put a half box of baking soda into the water in the bucket, and with a long screwdriver, poked a hole in the acid bag to let it drain out.

After the bucket fizzed away the acid and baking soda, I pulled the cylinder out with a stiff wooden dowek, and parked it on a wooden plank.

I then swabbed a cheap toothbrush with baking soda, and brushed away at all the loose acidic scum and crud. I was astounded to find that after a few go-overs with this, the cylinder cleaned up like the day it left the factory. I ran upstairs to rinse it off in clean tap water... Beautiful... Seconds later, a thin orange tinge crept over it... I grabbed another cheap toothbrush and applied a layer of 20w50 oil to it all over, just so I didn't rust the * out of it.

I scrubbed off the internal surfaces of it with paper towels, removing any excess oil (and the rust that was in it), as well as any contact points (like where the gaskets go). All shiny? I put a thin film of oil back on the inside of the cylinder (once it was all clean, It was amazing how much blacker the paper towel was even after the acid), and after a few bumbled attempts, I put the piston in.

Then, I removed it, and put the bottom gasket on (DER!), and repeated the insertion.

With the plug gapped, the head in place, and the head bolts torqued, I checked the carb/air filter, and fired it up.

No gas was getting to the engine... So I goosed the carb with a little Chemtool (figuring that the heavy oil in there would compensate for the lean-ness and no lube in the volatile cleaner)... The scoot roared to life, sucked Gas down the tube, and ran like a dream... A few adjustments to the carb to get the idle down, and I'm thrilled.
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