While we can do our very best to service our machinery, in some situations, as a result of continued wear and tear, components can become ineffective. In this blog, our Managing Director, Muz answers some of the most frequently asked questions from our customers about crankshaft balancing.

crankshaft balancing

Why is it important to balance a crankshaft?

Dynamically balancing a crankshaft is a critical process to ensure longer engine life by making changes to the counterweights. These changes are made to compensate for the weights of the moving components attached to it such as the connecting rods and pistons etc. An engine’s crankshaft must be in balance in order for it to operate smoothly and efficiently, and although the manufacturer will have balanced the crankshaft to some degree, due to time and cost constraints, they are often only balanced to coarse tolerances. This is why it’s imperative to ensure your crankshaft is expertly balanced to suit your requirements.

How do you balance a crankshaft?

When it comes to balancing a V engine crankshaft, bob weights are added to the rod journals and the rotational imbalance is measured and modified to come within the tolerance. Conventional straight 4 and 6 cylinder crankshafts are balanced by removing mass from the counterweight. The balance process is then carried out by removing mass from designated areas, usually by drilling, until the total is correct to compensate for the engine components. With some specialist crankshafts, they can be balanced by adding mass to counter the unbalanced forces. Balancing each component separately and then as a complete rotating assembly is imperative to eliminating any balance issues along the way. This means balancing the flywheel, front damper and clutch assembly as this is where balance problems can arise from, as well as from the crankshaft itself.

Here’s two example of crankshafts which we’ve carried out dynamic balancing on in our factory. In the first image, we calculated and manufactured a suitable bobweight in order to carry out accurate balancing. The second image shows a straight 6-cylinder crank flywheel and clutch assembly, complete with pistons and conrods.

Custom Bobweights for Crankshaft Balancing

What causes a crankshaft to become unbalanced? 

There are a number of reasons why a crankshaft may become unbalanced including:

  • Manufacture error for the crankshaft and other ancillary units
  • Fitting new flywheel and clutch covers which aren’t balanced correctly
  • Overheating of the crankshaft due to a lack of lubrication causing distortion

How do you know when a crankshaft needs balancing?

If you notice decreased performance of your engine, excessive vibration, noise or heat, this is an indication that the crankshaft requires balancing. If left unresolved, it can cause excessive wear and tear on the engine and result in shorter engine life. Regular checks on the balance of your engine components is prudent, but it becomes essential to do so when a number of factors have taken place. These may include:

  • If the flywheel has been lightened, replaced or additional bolts have been added to it
  • If the clutch has been replaced
  • If the crankshaft has been modified (straightened, knife-edged etc.)
  • The piston or connecting rod combination have been changed
  • If there is excessive vibration after refurbishing a crankshaft i.e. after grinding the journals or replacing other running gears

What are the overall benefits of a balanced crankshaft?

When a crankshaft is in balance, you will see a number of benefits such as a smoother, more powerful and efficient engine.

Can all crankshafts be balanced? Is there any point they become beyond repair?

There are some situations in which the crank cannot be balanced, for example if it is bent beyond reasonable repair.

How long does it take to balance a crankshaft?

The length of time it takes to balance your crankshaft totally depends on a number of factors including the type of crankshaft, level of unbalance and its overall condition. We generally ask our customers to allow 2+ days. This gives us enough time to inspect, assess, balance and quality check your crank. If you require a faster turnaround, you can get in touch with our team to check our express service availability.

How much does it cost to balance a crankshaft?

Again, this completely depends on the size, type and complexity of the work required i.e. the balance grade, lightening, if weight needs to be added etc.

Which industries use crankshaft balancing services? 

A number of industries require crankshaft balancing. These can include motorsport, racing, vintage vehicle restoration, diesel generators and compressors etc.

How can WDB Ltd help?

We specialise in single cylinder to V16 crank assemblies, including:
  • Flywheels
  • Clutch covers
  • Match weighing rods and pistons
  • Knife edging
  • Lightening
We also have extensive experience in the balancing of high speed magnetic rotors – you can find out more about this in our previous blog here. 
Do you have a crankshaft or rotating assembly that requires balancing?