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The harmonic balancer (vibration damper) on the front of the crankshaft is one of the parts 560SL owners talk about most. It is a rubber-bonded part, and after decades the rubber can deteriorate. When it fails, it can cause serious damage, so it is worth checking.
What the balancer does
The balancer is mounted to the front of the crankshaft and drives the accessory belts. Inside, an outer ring is bonded to an inner hub through a rubber layer. The rubber absorbs torsional vibrations from the crankshaft. On the M117 V8, it also carries timing marks used for ignition timing.
Why it fails
With age, heat and oil contamination, the rubber layer hardens, cracks and can separate. The outer ring can then shift or walk forward relative to the hub. In the worst case, it can come loose. Owners discuss this most often on the 560SL’s 5.6-liter M117. How common failures are is hard to measure; I treat it as a known age-related risk rather than a certain failure.
Failure symptoms
- A wobble visible at the front pulley with the engine running
- Belts throwing or wearing unevenly
- A new vibration or noise from the front of the engine
- Timing marks that no longer line up with the true position, giving odd timing readings
- Visible cracks or bulging rubber between the hub and the outer ring
Inspection
- With the engine off, look closely at the rubber layer between the hub and outer ring. Look for cracks, gaps or rubber pushed out.
- Make a paint mark across the hub, the rubber and the outer ring. Check later whether the marks stay aligned. If they separate, the ring is slipping.
- With the engine running, watch the pulley face from the side for wobble. Keep hands and clothing clear.
Replacement
Replacing the balancer requires removing the fan and shroud, the belts and the crankshaft center bolt. The center bolt is tightened to a very high torque and needs the correct tools and a way to hold the crankshaft. Use the factory procedure and torque figure. Many owners have it done by a specialist. Use a quality balancer from a known supplier; quality varies.
Why it matters
If the outer ring comes loose, it can damage the radiator, hoses, the fan and the timing cover, and leave you stranded without belt-driven accessories. Compared with that, preventive inspection and replacement on a car with an original or unknown balancer is reasonable.
Cost
The part cost is moderate. Labor depends on the shop and how hard the bolt is to remove. Combining it with belts, hoses and the water pump saves labor. See belts and the 560SL buying guide.
Quick answers
- Do other R107s have the same issue? All rubber-bonded balancers age; the 560SL is discussed most.
- Can I drive with a cracked balancer? Not safely for long; replace it.
- How often should it be replaced? There is no fixed interval; inspect regularly and replace on age and condition.
- Will it affect timing? A slipping outer ring makes the timing marks wrong.
