16.EN.0004
Arm and Shaft
Engine Arm and Shaft is a mechanical linkage group of arms, shafts, bushings and pins that transmits motion to the relevant points inside the engine. Read the guide
All Arm and Shaft products 1
What is Engine Arm and Shaft?
Engine Arm and Shaft is a mechanical linkage group on heavy commercial vehicle engines, made up of arms, shafts, bushings and pins that transfer motion from one point to another. Its role in the engine is to keep the moving parts working in sync and to pass that motion to the relevant points. Because it works under constant motion and varying load, the parts that wear first are usually the bushing surface, pin holes and shaft bearings; once clearance develops, vibration and knocking begin. In workshop language this group is also known as the “arm and shaft kit” or “bushing and pin set”.
How does Engine Arm and Shaft work and what parts does it cover?
Motion is transferred from one bearing to another through the arm and shaft; bushings and pins keep these axes in position and allow free rotation. The part groups covered by this category are:
- Arm body: The main arm that carries the motion and connects to the shaft.
- Shaft: The rotating part that carries motion between the arm and the other connection point.
- Bushing: The bearing element that allows the shaft or pin to rotate in its seat, and is replaced when worn.
- Connecting pin: The pin that fixes the arm to the shaft or housing and prevents axial movement.
- Support and fixing elements: Brackets, nuts and connecting parts that keep the arm in position.
Engine Arm and Shaft variants
- Complete arm and shaft set: Sets where the arm, shaft, bushing and pin come together; preferred when more than one part is worn.
- Single arm: Used only when the arm body is replaced; may be enough if the other parts are sound.
- Bushing and pin set: A small kit of parts renewed when clearance increases at bearing and connection points.
- Support and fixing group: Chosen when elements such as brackets and nuts need to be replaced separately.
How to choose the right Engine Arm and Shaft?
To select, first compare the reference marks on the removed part, the bolt hole layout and the pin seat shape. Do not take a part without checking engine type and serial information. Even within the same model series of brands such as Mercedes-Benz, MAN, Scania, Volvo and DAF, different layouts can exist, so choosing by model name alone is a mistake. Parts on the cylinder head, valve, exhaust and cooling side are outside the scope of this page; please look at the related sister categories.
| Criterion | What to check | Why it matters |
|---|---|---|
| Engine type | Engine code and serial information | Different arm layouts can exist within the same brand |
| Reference mark | Casting or scribe mark on the removed part | Shows the correct position and orientation |
| Connection point | Hole layout and pin seat shape | A non-matching part restricts movement and creates clearance |
| Bushing and bearing surface | Scoring or wear on the surface | Can be the source of clearance and knocking |
| Complete or single | Whether bushings and pins are included | Missing parts lengthen installation |
| Material and workmanship | Surface evenness and sound casting | Decisive for strength and part life |
Installation and maintenance points
- Lubrication: Bushings and pins are oiled with clean oil before fitting; dry assembly speeds up wear.
- Seat cleaning: Pin and bushing seats are cleared of burrs and dirt; an off-centre part wears quickly.
- Direction check: If bushings and pins are fitted in a set direction, the manufacturer's marks are followed; the part is checked to seat correctly rather than forced in.
- Securing: Nuts and brackets are tightened in the specified sequence and evenly; loose fixing increases vibration.
- Clearance check: After fitting, the arm is gently moved by hand to check for clearance and friction.
- Part integrity: A new part and a fatigued old part are not fitted together; a group replacement is preferred where possible.
Common faults and solutions
- Knocking or ticking noise: Clearance in bushings and pins; the related bushing and pin are replaced.
- Vibration and sticking arm: Friction or off-centre seating in the bearing; the seat is cleaned and the part is positioned correctly.
- Pin walking and loosening: Fatigue of the fixing elements; the pin and nut are replaced, and the connection is retightened.
- Fine crack on the arm: Fatigue and continuous load; the arm body is replaced.
- Oil traces and wear on the shaft: Lack of lubrication or seal leakage; lubrication is checked and the worn shaft is renewed.
Frequently Asked Questions
How is an Engine Arm and Shaft fault identified?
Ticking noise, knocking, vibration and a feeling of clearance during movement are the most common symptoms. Since these can also come from other mechanical points, the area should first be checked by hand and by eye.
Can a bushing and pin be replaced on their own?
A bushing and pin set can be replaced alone; if the shaft and arm surfaces are sound, this is usually enough. If there is clear wear on the surfaces, replacing the complete group is a safer result.
How do you decide between a complete group and a single arm?
Look at where the removed parts are worn. If a single arm is damaged, replacing only that part may be enough; if several parts are fatigued, the complete group is the better choice.
Why do arms and shafts wear quickly?
Constant motion, changing load and lack of lubrication speed up wear. Dirty oil and loose fixing also cause early deterioration of the surfaces.
What is the first check after fitting a new part?
The simplest check after fitting is to move the arm gently by hand and check for friction. After the engine is started, the noises should be listened to again and the fixing elements checked once more.