Garden Railways - crud

Various means,some depending on whether the wheels are plastic or metal.

Isopropyl alcohol ,Usaully just known as IPA is a good solution to soften the dirt . Don't mess about buying a small bottle in a shop. Get 5 litres for not a lot more cost from a chemical supplier. You can use it to clean track as well ,clean track is essential for clean wheels and garden lines tend to need a bit of cleaning at times. Remove the dirt from wheels with tissue, cotton buds (Q Tips, N America), or a clothe of suitable fine material. A fine fibre glass pencil is also useful but more appropriate on metal wheels. Similar a scraping tool such as a fine screwdriver or old bluntish scalpel blade can be useful but on plastic wheels could if care is not taken damage them and leave rough bits which in future will pick up and hold dirt.

Mechanical assistance may assist such as spinning the wheel set with a Dremel like tool or using one to hold a fiberglass brush. Take care not to over speed the wheelsets, axle bearings aren't designed for the high revs that can be reached and may get hot and melt and even if they don't you can put in year or so wear in a few minutes. Been there done that.

Finally if the wheelsets are easy to pop out and you have access to an Ultrasonic bath you can do a bulk clean to get the worst off. In my experieince the small ones that can be bought at shows etc arn't really that good,the one in the lab at work was great.

G.Harman