Yanmar Super Forte AF-22 to AF-33 filters: air, oil, fuel and transmission

The filters of your Yanmar Super Forte AF-22 to AF-33 are the cheapest maintenance with the biggest effect on power and lifespan. Below you'll find out which filters the AF series has — air, oil, fuel, and an often forgotten transmission line filter — with the cleaning and replacement intervals from the original Yanmar manual and the correct procedure.

Suitable for the entire series: Yanmar Super Forte MARK III AF-22, AF-24, AF-26, AF-28, AF-30 and AF-33.

Why filters are so important on this tractor

A saturated air filter directly costs power and makes the engine smoke blacker; a clogged fuel filter is one of the most common causes of poor starting and rough running, especially after a period of standstill. On a tractor of this age, a fresh set of filters is therefore often the first and cheapest step to get it running smoothly again.

The air filter

The AF series has a dry paper air filter element that stops the dust being drawn in, preventing wear on the cylinder liner and piston rings. The manual gives clear intervals, depending on how dusty your work is:

Even if you don't reach those hours, replace the element at least once a year. To clean it: remove the cover, take out the element and blow it with low air pressure from the inside out so the dust exits on the dirty (outer) side. Blow carefully and don't damage the paper — a torn element lets dust through and must always be replaced.

The fuel filter

The fuel filter keeps dirt and water out of your injection system. Drain the water regularly and replace the element according to schedule. If the engine runs unevenly or loses power under load, a clogged fuel filter is often the culprit.

Important — bleeding after replacement. If you've replaced the fuel filter element (or the tractor has run dry), you need to bleed the fuel system, otherwise it won't start. The manual describes this as follows:

This bleeds the system and allows the tractor to start again. Do not run the starter motor for more than about 10 seconds at a time.

The oil filter (engine oil element)

The engine oil element is a spin-on cartridge. The manual recommends replacing it every 300 hours — approximately every 2 to 3 oil changes. Procedure: first drain the old engine oil and unscrew the cartridge (counterclockwise) with a filter wrench. Apply a thin layer of fresh oil to the rubber ring of the new filter and tighten it firmly. After changing, start the engine and check that the oil pressure light goes out; then check the oil level again with the dipstick and top up if necessary.

The forgotten fourth filter: the transmission line filter

What many owners don't know: besides the engine filters, the AF series also has a line filter in the transmission/hydraulic system (the transmission oil filter), also a cartridge type. The manual prescribes replacing this filter every 300 hours . Drain the transmission oil, unscrew the old cartridge counterclockwise, lightly lubricate the rubber ring of the new one with oil and tighten it firmly. Then briefly start the engine to circulate the oil, switch off, and check the oil level — top up if necessary. Skipping this filter is a common mistake that eventually leaves the hydraulics and the wet brakes running dirty.

Don't forget the radiator screen

Strictly speaking not a filter, but a screen that you still need to keep clean: the radiator screen catches straw and dust before the radiator. Pull the screen up and out and remove straw and dirt — before and after work. A clogged screen is a common cause of overheating, so include it in your filter round.

Watch out for the engine difference with engine parts

The air, fuel and oil filters fit all AF models, but as soon as you go deeper into the engine block — think of head gaskets — the difference between the 82 mm engine (AF-22/AF-24) and the 84 mm engine (AF-26 to AF-33) matters. These parts are not interchangeable. Always check your engine number before ordering engine parts.