Technical - How-To


Parkerizing is an inexpensive rust-resistant finish that Harley-Davidson used on nuts and bolts, and many other plain steel external parts. Technically, it's called a phosphate conversion coating, but in practice, it's a simple process that you can do at home – as easy as boiling water.

Simplified Process

Supplies and Equipment

You are going to need some supplies and equipment. How much? How big? It depends on whether you're going to do just nuts and bolts, or if you're doing a complete K or XL (or any other Harley for that matter) restoration. Some parts, like the rear motor mount, K/XLH oil tank mount, and others, are pretty large, and require bigger pots.

Manganese Phosphate Parkerizing solution

There are many suppliers of this stuff. One pint will easily do a motorcycle or two, but a gallon will last a lifetime. Look at the mixing directions – different suppliers sell different concentrations. Check the shipping costs – sometimes shipping a gallon is the same price as shipping a pint.

I bought a gallon of Brownell's product as it seemed more concentrated than other brands I investigated.

The directions that come with your solution will tell you how to dilute it - with plain water. If you live in a hard-water area, you should consider using spring water or distilled water. Upon heating, the minerals will come out of hard water and stick to the bottom of your pot. Spring water is cheap.

Parkerizing solution is dilute Phosphoric acid with some manganese compound. It's nowhere near as nasty as that muriatic stuff, but you don't want it on you. So, long sleeves, gloves, and safety glasses.


Muriatic Acid

Hydrochloric acid, commonly known as Muriatic Acid, is available from a good hardware store or swimming pool supply store. A one-gallon jug of 31% to 36% acid should cost you about $6. Home Cheapo and other big-box stores sell some “Green” stuff that advertises “XX% less fumes”. The reason it fumes less is that it's only 20% acid, so you're paying a lot for some plain old water.

Concentrated hydrochloric acid will damage eyes, nose, ears, and skin, so wear appropriate personal protective equipment – long sleeves, gloves, and safety glasses. Use it outdoors and don't breathe this stuff.

Laboratories use 37% “Fuming” Hydrochloric Acid. It's unstable at higher concentrations. Don't get confused – battery acid is Sulfuric Acid - and it's a totally different animal.

Remember: Always add acid to water - never the reverse.



Look on the bottom of the jugs these two chemicals came in – they probably say HDPE and have a #2 recycling symbol. Gallon milk jugs are HDPE #2. Ones with screw caps are best. Folgers coffee containers are HDPE #2. These are good things for storing and using your chemicals.

Use a Sharpie marker to mark your containers “POISON” and what's in them. Add some skull and crossbones too. We don't want any horrible accidents!


Motor Oil

You're need enough motor oil to immerse your parts. Grab a quart or a gallon of whatever's on sale at your local auto parts store. Personally, whenever I add a quart of oil to anything, I put the empty oil jug upside down in a spaghetti sauce jar and let it drip. The jar fills up surprisingly fast with a mixture of various grades of oil, which can be used for Parkerizing or general lubrication needs.


Acid-Resistant Gloves

These neoprene gloves are great for working with most of the chemicals you'll encounter in your garage, but not for acetone or MEK. They're Ansell 08-352 or 08-354. I wear size 10. You can get them from Grainger for about $10. Amazon sells a pack of dozen pairs.


Pots and Pans

If you're just doing nuts and bolts, any stainless steel kitchen pot will do nicely. For larger jobs, like the K/XL rear engine mount, you'll need a large stock pot. Walmart sells this 16-Qt Stainless Steel Stock Pot with Metal Lid for about $12. Dollar stores and Asian grocery stores are also good sources for inexpensive cooking supplies.

You may want two of these babies – one for the hot water bath, and one for the Parkerizing bath.

It's best to have some way to keep your parts from sitting directly on the bottom while Parkerizing. Look for a stainless steel wire mesh colander or basket at the kitchen store that will fit inside, perhaps if you cut off the handles. A hardware store may yield some stainless wire mesh.



You'll need a heat source for the Parkerizing bath, and perhaps one for the hot water bath. A hot plate will do for nuts and bolts, but you may need to go larger. Many backyard barbeque grills have a “fifth burner”. Walmart sells this propane burner for about $60.

I use my barbeque's fifth burner for the hot water bath, and this propane burner for the Parkerizing bath.



You need a cooking thermometer to keep the temperature of the Parkerizing bath at 190 to 200 degrees. You should be able to find one for about $5. Once this falls down in the solution, you're not going to use it for anything else, so don't spend money on a fancy one.


Miscellaneous Tools

You have to get your parts out of the near-boiling hot water and Parkerizing baths, and the muriatic acid bath if you use it, so you'll need some stainless steel tongs. Stainless steel kitchen strainers are great for holding nuts and bolts and small parts. All available at Walmart or the dollar store for cheap.

Steel wire, preferably stainless steel, can be looped through nuts and washers and twisted into a knot.

It's unlikely you'll need to buy all of this stuff, but we've covered just about everything you could possibly need.

Proceed to Part II – Detailed Process