How to Inspect a Used Crankshaft Before Rebuilding Your Engine

Introduction

Rebuilding an engine can be a cost-effective way to breathe new life into your vehicle. But, to be honest, it's not as simple as swapping out parts and hoping for the best. One crucial aspect of engine rebuilding is ensuring that your used crankshaft is in good condition. So, how do you go about inspecting a used crankshaft? Let's dive into the details.

Visual Inspection: Check for Obvious Damage

First things first, give the crankshaft a thorough visual inspection. Look for any obvious signs of damage, such as cracks, scoring, or excessive wear on the journals and bearing surfaces. If you spot any of these issues, it's best to pass on that particular crankshaft and find another one.

Measuring Crankshaft Runout

Crankshaft runout refers to the amount of wobble or movement in the crankshaft as it rotates. Excessive runout can lead to uneven wear on bearings and other engine components, reducing the engine's performance and lifespan. To check for runout, follow these steps:

Secure the crankshaft in a vise, ensuring it's well-supported and won't bend during the process.

Attach a dial indicator to the vise and position it against the crankshaft's journal surface.

Slowly rotate the crankshaft, noting the maximum and minimum readings on the dial indicator.

The difference between these readings is the runout. Most engine manufacturers recommend a runout of 0.002 inches (0.05 mm) or less.

Checking Crankshaft Straightness

In addition to runout, you'll also want to check the crankshaft's straightness. A bent crankshaft can cause significant problems, including uneven pressure on the bearings and potential engine seizure. To check for straightness, you'll need a straightedge and a feeler gauge. Here's how:

Place the straightedge along the length of the crankshaft, ensuring it's well-supported.
Use the feeler gauge to measure the gap between the straightedge and the crankshaft at various points along its length.
If the gap exceeds the manufacturer's specifications, the crankshaft is bent and should be replaced.

Magnetic Particle Inspection

Sometimes, crankshaft damage isn't visible to the naked eye. In such cases, a magnetic particle inspection (MPI) can help reveal hidden cracks or flaws. This process involves magnetizing the crankshaft and applying iron particles, which will gather at any areas with cracks or imperfections. While MPI is typically performed by professionals, it's worth considering if you're unsure about a crankshaft's condition.

Practical Application: What to Look For

When inspecting a used crankshaft, keep an eye out for the following red flags:

Cracks or scoring on the journals or bearing surfaces
Excessive wear on the main or rod bearings
Deep scratches or gouges on the crankshaft
Excessive runout (more than 0.002 inches or 0.05 mm)
A bent crankshaft

Conclusion

Inspecting a used crankshaft before rebuilding your engine is crucial to ensuring optimal performance and longevity. By following these guidelines and keeping an eye out for potential issues, you'll be well-equipped to make an informed decision about the suitability of a used crankshaft. Happy rebuilding!