What the Washer Does, and What Happens Without It
An excavator pin joint has a steel pin, a steel bush in the bucket ear and a boss on the arm or link. The pin carries the load; the washers carry the side thrust. Two white nylon washers, one each side between ear and boss, set the side play, keep grit out of the face and stop steel touching steel when the bucket is pushed sideways in the cut. With the washers gone the bucket walks 5 to 10 mm on its pin, the bosses mushroom, the bush wears egg-shaped and the next pin change costs a line-boring job instead of two washers.
Size Range — Pin Ø 30 to 120 mm, Any Outside Diameter, Any Thickness
The washer is defined by three numbers: the pin it sits on, the boss face it bears against, and the gap it fills. The table gives the pin sizes we make for and the machine class each is typical of; the outside diameter and thickness are cut to your measurement, not taken from a list, so an odd number is no extra cost.
| Pin Ø (bore) | Typical machine class | Typical OD band | Thicknesses usually asked for (mm) |
|---|---|---|---|
| 30 | 1.5–2 t mini | 50–65 | 2 / 3 / 5 |
| 35 | 2.5–3 t | 55–70 | 2 / 3 / 5 |
| 40 | 3–4 t | 60–80 | 2 / 3 / 5 |
| 45 | 5–6 t | 70–90 | 2 / 3 / 5 / 8 |
| 50 | 7–8 t | 75–95 | 2 / 3 / 5 / 8 |
| 55–60 | 10–14 t | 85–110 | 3 / 5 / 8 / 10 |
| 65 | 13–16 t | 95–120 | 3 / 5 / 8 / 10 |
| 70 | 18–22 t | 100–130 | 3 / 5 / 8 / 10 |
| 80 | 20–25 t | 115–145 | 3 / 5 / 8 / 10 / 12 |
| 90 | 30–36 t | 130–160 | 5 / 8 / 10 / 12 |
| 100 | 40–45 t | 145–180 | 5 / 8 / 10 / 12 / 15 |
| 110 | 45–50 t | 160–200 | 5 / 8 / 10 / 15 |
| 120 | 60–80 t | 175–220 | 5 / 8 / 10 / 15 / 20 |
Machine class is a guide only: the pin diameter on the machine is the number that counts, and a 20 t machine from one maker may carry the 70 mm pin of another's 15 t. Bore is cut 0.5 to 1.0 mm over the pin, OD to the boss face or 5 mm under it, thickness to your gap in 0.5 mm steps; any thickness from 1.5 to 20 mm.
Need bucket pin washers and shims in a size, thread or material no catalogue lists? EKINSUN is a custom parts manufacturer: we make bucket pin washers and shims to your drawing, sketch or sample — nylon PA6, POM, UHMW-PE or steel — from 1 piece, quoted in 12 hours and shipped duties paid. Standard sizes can often be supplied from stock; the more pieces, the lower the unit price. Custom replacement parts →
Which Nylon — and When It Is Not Nylon
| Material | Density | Compressive strength | Service temp. | Where it is used |
|---|---|---|---|---|
| Nylon PA6, natural white (extruded) | 1.14 | ~90 | −40 to +100 | the standard bucket pin washer: tough, does not score steel, cheap; bore cut 0.5–1 mm over the pin for moisture swell |
| Cast nylon PA6-G (MC nylon), natural or blue | 1.15 | ~100 | −40 to +110 | washers above 150 mm OD and thick shims: cast blanks, lower internal stress, less swell than extruded PA6 |
| Oil-filled cast nylon | 1.14 | ~85 | −40 to +100 | joints that run dry for long periods; the oil bleeds to the face and halves the friction |
| Nylon PA66 | 1.14 | ~100 | −40 to +120 | higher stiffness and temperature, same machining; the choice near the exhaust side of the arm |
| UHMW-PE | 0.94 | ~20 | −100 to +80 | lowest friction and best wear in abrasive slurry, but soft: for light machines and dredging attachments only |
| Polyurethane 90–95 Shore A | 1.20 | elastic | −30 to +80 | a rubbery washer that also keeps grit out; used as the outer washer of a pair, never as the only thrust face |
| Steel shim, stainless 304 (1.4301) or zinc-plated | 7.9 | n/a | any | when the gap is under 1.5 mm and a nylon washer would be too thin to survive; laser-cut, see thin washers and shims |
| Aluminium 6061 / 7075 | 2.7 | n/a | any | not used on pins: aluminium galls against a steel boss and picks up grit; listed so the question is answered |
Moisture matters more than load. Nylon absorbs water: PA6 reaches 2 to 3 % in outdoor service and grows about 0.25 % in size for every 1 % it takes up. A washer bored dead on the pin in the workshop is tight on the pin after a wet week, which is why the bore is cut over size and why cast nylon, which swells less, is used for the large washers. The face load on a bucket pin washer is far below what the material can carry; it is the swell and the grit that decide how long it lasts.
What to Measure — Three Numbers and a Feeler Gauge
With the bucket hanging free and the pin in, push the bucket to one side and measure the open gap on the other with a feeler gauge or vernier; push it back and measure again. The two gaps are what the washers must fill, less 1 to 2 mm of total play so the joint can still take grease. Measure the pin diameter on the exposed end, and the diameter of the boss face the washer bears on. If the old washer is still there, a photo of it next to a rule replaces all three. We send a sketch back with the numbers before cutting.
Dealer Shim Kit or Washers Made to the Gap
For a current machine with pins and bosses still at the original size, the dealer's kit is matched to the machine and is the right buy. We make the washers where the kit stops.
| What you need | In the catalogue? | What we make |
|---|---|---|
| The dealer's shim kit for a current machine, pins and bosses still at original size | Yes — dealer parts counter | Buy it from stock; the kit is matched to the machine and we say so instead of quoting. Standard parts: ask us too — we may have them in stock. |
| Washers for a pin or bush changed to a non-standard size after line boring, or an odd thickness the kit does not carry | No | Turned from PA6 or cast nylon to the measured pin, boss and gap; from 2 pieces. |
| A set for an old or orphan machine with no parts listing, from a photo of the worn washer | No | Measured from the photo and the pin; sketch sent back for approval before cutting. |
| A mixed set for a fleet: five machines, three pin sizes, several thicknesses, one order | No | One order, one drawing per size, bagged and labelled per machine. |
| A shim under 1.5 mm thick | Not in nylon | Laser-cut steel or stainless shim instead; nylon that thin tears out under side load. |
The washers rarely travel alone: the trunnion pins and mounts and the pins themselves are made in the same order, the bushes on the spacers and bushings from a sketch route, and a washer that must insulate or resist chemicals is chosen by material on plastic and insulating washers. Thick and large steel washers are on custom washers machined to size.
What to Send
Pin diameter, boss face diameter, the gap on each side and the quantity; or a photo of the old washer next to a rule. The machine model helps but is not required. Sets are bagged per joint and shipped in about a week; quote in 12 hours.
Bucket Pin Washer FAQ
They take up the side play between the bucket ears and the arm or link boss so the bucket cannot walk sideways on the pin. Steel-on-steel side contact hammers the bosses and wears the pin and bush out of round; a nylon washer between the faces carries the side thrust, does not score the steel and can be replaced in minutes. The same washers sit on the link pins and the boom-to-arm pin.
Natural (white) PA6, extruded for washers up to about 150 mm outside diameter and cast (PA6-G, often called MC nylon) above that. Dry PA6 takes about 90 MPa in compression, runs from −40 to +100 °C and absorbs 2 to 3 % moisture in service, which is why the bore is cut 0.5 to 1 mm over the pin. Oil-filled cast nylon is the choice when the joint runs dry for long periods; PA66 when the washer sits near the exhaust side. Black PA6 is the same material with carbon black added for UV; white is what most machines carry.
With the bucket hanging free and the pin in, push the bucket hard to one side and measure the open gap on the other side with a feeler gauge or vernier; then push it the other way and measure again. The shim set should close the total to 1 to 2 mm of play, split between the two sides. Note the pin diameter (vernier on the exposed pin end) and the outside diameter of the boss face the washer sits against; those three numbers are the washer.
Yes, and when the machine is current and the pins and bosses are still at the original size, the dealer's shim kit is the right buy and we say so. We make the washers when the kit no longer fits: a pin or bush changed to a non-standard size after line boring, an old machine with no parts listing, a thickness the kit does not carry, or a mixed set for a fleet of different machines in one order.
Two pieces, one pair for one joint. A full bucket set (bucket pin and link pin, both sides) is four to six washers, and a fleet order is quoted per machine model. There is no tooling: washers are turned from rod or cut from sheet, so a single odd size costs the same per piece as the standard one.
Pin diameter, boss face diameter, the gap on each side and the quantity, or a photo of the old washer next to a rule. The machine model helps but is not required. No drawing is needed; we send a sketch back for approval before cutting.