Overview
This article presents seven essential tips for accurately measuring crankshaft end play, a critical engine building skill that ensures proper clearance between the crankshaft and thrust bearings. The guide covers everything from selecting the right measurement tools to understanding specification ranges and making necessary adjustments, emphasizing how proper end play (typically 0.002″-0.010″) prevents premature engine wear and failure.
Table of Contents
- Introduction to Crankshaft End Play Measurement
- What is Crankshaft End Play?
- Why is Proper End Play Measurement Important?
- Tip 1: Gather the Right Tools
- Tip 2: Proper Engine Preparation
- Tip 3: Mastering the Dial Indicator Setup
- Tip 4: Correct Measurement Technique
- Tip 5: Understanding Specification Ranges
- Tip 6: Adjusting End Play When Necessary
- Tip 7: Final Verification
- Conclusion
- Frequently Asked Questions
Introduction to Crankshaft End Play Measurement
When I first started working on engines over 20 years ago, checking crankshaft end play was one of those measurements that separated the rookies from the veterans. Crankshaft end play measurement is a critical aspect of engine building and repair that ensures your engine’s long-term reliability. The crankshaft is essentially the backbone of your engine, converting the up and down motion of your pistons into the rotational force that eventually gets your wheels turning.
Throughout this guide, I’ll walk you through seven practical tips for measuring crankshaft end play accurately, drawing from years of hands-on experience in professional engine building. Whether you’re rebuilding an engine from scratch or diagnosing a potential crankshaft issue, these tips will help you avoid costly mistakes and ensure your engine runs smoothly for thousands of miles to come.
And don’t worry – if you’ve been measuring end play by seeing how far your crankshaft slides when you push your car down a hill, you’re definitely doing it wrong (though it would make for an interesting neighborhood spectacle).
What is Crankshaft End Play?
Crankshaft end play refers to the small amount of axial (forward and backward) movement that a crankshaft is allowed within the engine block. This controlled movement is intentional in engine design, providing space for thermal expansion as the engine heats up during operation. Think of it as breathing room for your crankshaft.
End play is typically measured in thousandths of an inch (0.001″) or millimeters, depending on your engine’s specifications. Most modern engines require between 0.002″ and 0.010″ (0.05mm to 0.25mm) of end play, though the exact specification varies by engine make and model. This seemingly tiny tolerance is crucial – too much play can cause excessive bearing wear and even crankshaft damage, while too little can result in binding, overheating, and potential seizure.
When building an engine, checking piston to wall clearance and crankshaft end play are two measurements you simply can’t afford to skip. Both directly impact how your engine will perform under stress and throughout its service life.
Why is Proper End Play Measurement Important?
Understanding why crankshaft end play measurement matters can motivate even the most impatient mechanics to take their time with this critical procedure. First and foremost, accurate end play ensures proper oil film formation between the crankshaft thrust surfaces and the thrust bearings. This oil film is essential for reducing friction and preventing metal-to-metal contact that leads to premature wear.
When end play is excessive, you’ll likely experience symptoms like:
- Abnormal clutch operation and engagement
- Unusual crankshaft movement when the clutch is depressed
- Inconsistent timing chain tension
- Accelerated thrust bearing wear
- Oil leaks from the rear main seal or front crankshaft seal
Conversely, insufficient end play can cause the crankshaft to bind, creating excessive heat and potential bearing failure. According to Engine Builder Magazine, thrust bearing failures are among the most common yet preventable engine failures seen in repair shops today.
Taking the time to properly measure crankshaft end play isn’t just about following procedure – it’s about ensuring your engine rebuild or repair will stand the test of time. After spending hours on other aspects of engine work like cylinder bore taper measurement, the last thing you want is to have the engine fail because of improper crankshaft end play.
Tip 1: Gather the Right Tools
Like any precision job, measuring crankshaft end play starts with having the right tools at your disposal. You wouldn’t perform surgery with kitchen utensils, and you shouldn’t measure critical engine clearances with inadequate tools either.
Here’s what you’ll need:
- A quality dial indicator with magnetic base (preferably reading in 0.001″ increments)
- A sturdy mounting surface (the engine block itself works well)
- Pry bars or large screwdrivers (for applying force to the crankshaft)
- Clean shop rags
- Engine assembly lubricant
- Your engine’s service manual with the correct end play specifications
Investing in quality measurement tools pays dividends in accuracy and reliability. A good dial indicator should have smooth movement with no sticking or jumping, and a magnetic base with enough strength to stay firmly in place during measurement. The Starrett or Mitutoyo dial indicators are excellent choices that have served me well over decades in professional engine building.
Before starting, ensure all your tools are clean and in good working condition. Even a tiny speck of dirt can throw off a measurement when you’re working with tolerances measured in thousandths of an inch.
Tip 2: Proper Engine Preparation
Accurate crankshaft end play measurement begins with proper engine preparation. If you’re working on an assembled engine, ensure it’s at room temperature – thermal expansion can affect your readings. For an engine rebuild, this measurement should be taken during the assembly process, after the crankshaft and main bearings have been installed.
Start by ensuring the crankshaft and bearing surfaces are impeccably clean. Even minute debris can skew your measurements or, worse, cause damage when the engine runs. Apply a light coat of clean engine assembly lube to the thrust bearing surfaces – these are the bearing faces that control end play, typically located at the center main bearing position in most engines.
When installing the crankshaft, pay special attention to the thrust bearing installation. Unlike the other main bearings that primarily handle radial loads, thrust bearings have flanges that extend beyond the bearing shell to control axial movement. If your engine uses separate thrust washers rather than flanged bearings, ensure they’re installed in the correct orientation.
Before taking measurements, torque the main bearing caps to specification in the correct sequence. This ensures the bearings are properly seated and provides accurate end play readings. Remember that engine block deck surface preparation and main cap torquing are both critical to maintaining proper crankshaft alignment.
Tip 3: Mastering the Dial Indicator Setup
Setting up your dial indicator correctly is perhaps the most critical aspect of obtaining accurate end play measurements. Position the magnetic base on a stable surface of the engine block – I prefer the front of the block near the timing cover area for most in-line engines, or on the side of a V-configuration engine.
Orient the dial indicator so its plunger contacts the end of the crankshaft, typically at the crankshaft pulley mounting flange or the flywheel mounting flange, depending on which end is more accessible. The plunger should be positioned parallel to the crankshaft’s centerline to ensure you’re measuring true axial movement.
Once positioned, preload the indicator by compressing the plunger slightly (about 0.050″ or 1.25mm) and zero the dial. This preloading ensures the indicator has enough travel in both directions to accurately measure the crankshaft’s movement. Check that the indicator’s magnetic base is securely attached and won’t shift during measurement – a moving base is one of the most common causes of inaccurate readings.
Before taking your official measurements, practice moving the crankshaft back and forth while watching the indicator to ensure everything is working smoothly. The dial should move consistently without jumping or sticking, indicating both proper setup and a properly installed crankshaft.
Tip 4: Correct Measurement Technique
With your dial indicator properly set up, it’s time to take the actual measurement. This requires applying force to the crankshaft to move it to its extreme positions. There are two primary methods for this, and I recommend using both for verification.
For the first method, use a large screwdriver or pry bar to push the crankshaft all the way forward (typically toward the front of the engine). Apply steady, moderate force – you’re looking to move the crankshaft against its thrust surface, not bend anything! Note the reading on your dial indicator, then use your pry bar to push the crankshaft all the way in the opposite direction. The difference between these two readings is your crankshaft end play.
The second method involves using the flywheel or flexplate. If installed, you can pull and push on the flywheel/flexplate to move the crankshaft back and forth. This sometimes provides more consistent force, especially on larger engines.
For the most accurate results, perform the measurement at least three times and average the readings. Consistency between measurements indicates you’re doing it correctly. If you get varying results, check your dial indicator setup and ensure nothing is moving that shouldn’t be.
Remember to apply force gently but firmly. As one of my mentors used to say, “You’re measuring a precision part, not wrestling an alligator.” The goal is controlled movement, not brute force that might damage bearings or affect the reading.
Tip 5: Understanding Specification Ranges
Once you’ve obtained your crankshaft end play measurement, it’s time to compare it to the manufacturer’s specifications. These specs aren’t arbitrary – they’re carefully determined values that balance the need for expansion room against the stability requirements of the engine.
Most engines specify end play as a range rather than a single value – for example, 0.004″ to 0.008″ (0.10mm to 0.20mm). Ideally, your measurement should fall within this range, though many professional engine builders aim for the middle to upper portion of the range to allow for thermal expansion.
If your measurement falls below the minimum specification, the crankshaft may bind as the engine heats up, potentially causing catastrophic failure. Conversely, excessive end play beyond the maximum specification can lead to abnormal thrust bearing wear, oil leaks, and inconsistent timing.
It’s worth noting that different engines have different end play requirements. High-performance engines often specify tighter tolerances, while heavy-duty diesel engines might allow more end play. Always consult the factory service manual or trusted aftermarket sources like Clevite Bearing’s technical resources for the correct specifications for your specific engine.
Tip 6: Adjusting End Play When Necessary
If your crankshaft end play measurement falls outside the specified range, adjustments will be necessary. The method for adjustment depends on whether you need to increase or decrease the end play.
When end play is too tight (below specification), you’ll need to create more clearance. This typically involves:
- Replacing the thrust bearings with thinner ones (if available)
- Carefully machining the thrust faces of the block (a job for professional machine shops)
- In some cases, replacing the crankshaft if it has unusual wear patterns or damage
When end play is excessive (above specification), you’ll need to reduce the clearance by:
- Installing oversize thrust bearings (often available in 0.001″ or 0.002″ oversize)
- Using specialized thrust bearing spacers in some applications
- In severe cases, having the crankshaft thrust surface built up and reground (another machine shop operation)
Most production engines won’t require these adjustments if using new, quality parts. However, high-performance builds or engines with worn components often need thrust bearing adjustments to achieve proper specifications.
If adjustment is needed, always recheck your measurements after making changes. This iterative process ensures you achieve the correct clearance without going too far in either direction.
Tip 7: Final Verification
After achieving the correct end play measurement, a final verification step can provide peace of mind that your work is correct. This step is especially important if you had to make adjustments to achieve the proper specification.
For the final verification:
- Remove and reinstall the dial indicator setup from scratch
- Have another person take the measurement if possible (a fresh perspective can catch errors)
- Check end play at multiple crankshaft rotation positions (every 90 degrees)
- Verify that the crankshaft rotates freely through its entire range of motion
If you’re building a complete engine, consider measuring end play again after the oil pan and timing cover are installed. In some engines, these components can affect end play if they’re not properly aligned or if gaskets are compressed unevenly.
Once verified, document your measurements for future reference. I keep a build sheet for every engine with all critical measurements, including crankshaft end play. This documentation is invaluable for troubleshooting or future rebuilds.
Remember that proper end play is just one aspect of a well-built engine. It works in conjunction with other critical measurements like rod bearing clearance, main bearing clearance, and proper torque sequences to ensure engine longevity.
Conclusion
Mastering crankshaft end play measurement is an essential skill for any serious engine builder or mechanic. These seven tips provide a comprehensive approach to obtaining accurate measurements that will help ensure your engine’s reliability and performance.
From selecting quality tools to understanding specification ranges and making necessary adjustments, each step builds upon the last to create a systematic approach to this critical measurement. The time invested in properly measuring and setting crankshaft end play pays dividends in engine longevity.
Remember that patience is key when taking precision measurements. As we say in the shop, “Measure twice, build once.” Your engine’s crankshaft is its beating heart, and giving it the proper room to operate – not too much, not too little – sets the foundation for thousands of trouble-free miles.
Whether you’re rebuilding your first engine or your fiftieth, following these seven tips for crankshaft end play measurement will help ensure your build meets professional standards and delivers the performance and reliability you expect. Your crankshaft will thank you for the attention to detail, even if it never says so directly.
Frequently Asked Questions
What happens if crankshaft end play is too tight?
Insufficient end play can cause the crankshaft to bind as the engine heats up, leading to excessive heat, thrust bearing failure, and potential crankshaft damage. This typically results in catastrophic engine failure if not corrected.
How often should crankshaft end play be checked?
Crankshaft end play should be checked during engine rebuilds, after major repairs involving crankshaft removal, or when diagnosing symptoms of thrust bearing failure. It’s not typically part of regular maintenance.
Can I measure end play without removing the engine?
On some engines, end play can be measured with the engine in the vehicle by accessing the front crankshaft pulley or rear flywheel area. However, measurements are more accurate with better access to the crankshaft.
What are the symptoms of excessive crankshaft end play?
Symptoms include clutch operation problems, abnormal crankshaft movement when the clutch is depressed, timing chain noise, and oil leaks from front or rear crankshaft seals. You might also notice unusual engine knocking or clicking sounds during acceleration or deceleration.
Is crankshaft end play different for diesel engines?
Yes, diesel engines often have different end play specifications than gasoline engines, typically allowing slightly more end play. Always consult the specific engine’s service manual for correct specifications.