Engine Block De Rust In Molasses Bath.

A rebuild mostly begins with a bare engine block. A tear down and rebuild of an engine that has been in frequent use is easy to degrease and clean, but an engine block that has been sitting around unused for several years and affected with heavy surface rust along with crud and muck in the water ways will need more than a squirt of degreaser and a high pressure wash to clean.

A very simple, cheap and effective method of cleaning a rusty engine block can be made like new again within three or four weeks immersion in a molasses bath. This cleaning method is well known in vintage car, truck and motorcycle circles.

Method:
Take one metal or plastic 120 litre (44gal) drum and cut in half to use as the bath container.
Make a trip to the local rural retail supplier and purchase 2.5 or 3 litres of raw stock feed grade molasses, ($8.50AU) feed grade molasses has the correct grade of phosphorus to create the chemical reaction on rust (Iron Oxide).

The Treatment Process Is Called Chelating.

Add some tap water to the bath, then add the full container of molasses which is a very very thick treacle like substance and has a very strong smell, stir the molasses into the water until it is completely mixed in. Lower the block into the bath, then add enough water to cover the engine block by about 1.5 inches, a small amount of evaporation will occur, but that will depend on the temperature in your area, just add extra water when required.

• High pressure wash and degrease the engine block before lowering the block into the molasses bath.
• The Molasses wont remove grease or paint left on the engine block, molasses will only remove rust or oxides.
• If a camshaft (jack shaft) happens to be difficult to remove from the engine block, the molasses will help to dissolve the rust and crud around the bearings which will enable safe removal when giving the block the final cleaning.
• The bare Kent engine block can be lifted by one person, but you may prefer to use a chain block to remove and replace the engine block.
• Once every seven days remove the engine block and high pressure wash, this helps to remove the dissolved rust and crud.
• Agitate the bath every third day simply by lifting and lowering the engine block into the bath once or twice.
• At three weeks immersion in the bath, the molasses should have pretty well done it’s job, if you are not happy with the result, leave the block in for another week.

But don’t leave the block in the bath for more than four or five weeks, as time passes, it will really begin to eat into weak parts of the cast iron metal.

The photo above was taken before the molasses bath treatment, the scale and rust is not to bad, but there was  a considerable build up all the same, and it was much the same throughout the entire water jacket area.

Here is a strange effect, the outline of the cylinder block can be easily seen, this was taken after about a week in the bath, it shows that the molasses is really working at eating/dissolving the rust.

The first lift and inspection, at nearly two weeks, the molasses simply works wonders on rusty cast iron, the jack shaft had quite a bit of rust before immersion, but photo shows how clean it is becoming.

Now we are at the final lift and drain stage, and ready for the last high pressure wash, once the pressure wash is complete, the block needs to be blown dry with compressed air as quickly as possible because if any moisture remains on bare cast iron it will rust in minutes.

It is surprising how much rust can be present in cast iron without you realizing it. When we were inspecting the top of the block, there was a lot of heavy pitting revealed, this particular block will be skimmed or decked anyway, but you would not want to torque a cylinder head and gasket down over a weak spot on the block like this which is around the water jacket passages, that would mean trouble for sure at later date.

Now we can see the result of the rust removal, the cast iron in the water jacket area is quite clean, the external metal of the block is like new, years of rust and crud build up has almost been removed.

This is the Kent tall block finally cleaned, dried and painted as near as I could find to Massey Ferguson Grey. Work will begin soon with decking of the top of the block, re-boring of the cylinders, and probably line boring of the steel capped mains, then the fun begins.  The brass freeze plugs, or welch plugs as we call them will be inserted into the block after all of the machining operations have been completed.