CHAIN DRIVE ALIGNMENT: HOW TO PROPERLY ALIGN YOUR FRONT AND REAR SPROCKETS
Proper motorcycle chain drive alignment is essential for a smooth-running drivetrain. Whether you're installing a belt to chain drive conversion kit, installing a new rear wheel, or building a custom chopper from scratch, checking your front and rear sprocket alignment is a step you should never skip.
WATCH VIDEO: HOW TO PROPERLY ALIGN YOUR FRONT AND REAR SPROCKET
Watch Tim demonstrate how to check for front and rear sprocket alignment on a custom Harley-Davidson EVO Chop he is currently building in his shop. His build features a Gasbox Reno 5 Speed Full Rigid Frame.
The video covers checking a straight alignment rod, measuring the gap between sprockets, comparing sprocket offsets, and using a different style sprocket and sprocket spacers to achieve the proper alignment on his project.
Tim's newest project a Harley-Davidson Big Twin Evo in a Gasbox Reno frame.
WHY IS MOTORCYCLE SPROCKET ALIGNMENT IMPORTANT?
Your front and rear sprockets need to sit in the same plane so the chain runs straight between them. When the sprockets are misaligned, the chain can track against the sides of the sprocket teeth, causing uneven wear and unnecessary stress on drivetrain components.
Improper chain alignment can lead to several problems, including:
- Uneven sprocket wear: A misaligned chain can wear one side of the sprocket teeth more quickly than the other.
- Premature chain wear: Side loading and friction can shorten chain life.
- Poor chain tracking: The chain may run crooked or rub against surrounding components.
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Increased risk of derailment: Severe misalignment can contribute to the chain coming off a sprocket, potentially creating a dangerous situation.
Checking alignment is especially important after installing new sprockets, converting from belt drive to chain drive, replacing a rear wheel, or modifying a motorcycle's drivetrain. Even if your motorcycle looks completely stock, don't assume its components are original. Previous owners may have installed a different rear wheel or made other changes that affect the chain line.
A long straight rod is a good measuring tool to have because it can get in hard to reach spots on custom builds.
WHAT YOU'LL NEED TO CHECK CHAIN DRIVE ALIGNMENT
There are several tools available for checking motorcycle sprocket alignment, including laser alignment tools, mechanical, and purpose-built gauges. You could also use some angled steel or aluminum long pieces but depending on bike it may have some clearance issues. In this instance, Tim recommends a straight piece of round stock that is long enough to span the distance between the front and rear sprockets.
You'll need:
- A verified-straight alignment rod or piece of round stock
- Small squeeze clamps
- A flat surface for checking the rod
- Calipers, if you want to measure alignment gaps
- Appropriate tools for removing and installing sprockets and spacers
The most important tool is a straight, reliable reference. An alignment rod that bends, wobbles, or has an uneven surface can give you inaccurate readings and lead to incorrect adjustments.
Top is a good gauge, it rolls flat and true to the level welding table with no gaps, The bottom is a bad gauge, it wobbles when rolled on the table and has gaps on either end.
CHECK YOUR ALIGNMENT ROD BEFORE USING IT
Before using the rod as a gauge, roll it across a known-flat surface and watch how it moves. Similar to checking if a pool cue is straight, you want to see that the rod rolls consistently without noticeable wobble or lifting away from the surface in any fashion.
You can see this is clearly lifting up significantly at the ends of the rod from the table. This is not a good gauge to use.
Pay particular attention to the ends and make sure they do not flop up in anyway. A bent or uneven rod can create a misleading gap at the rear sprocket, making it look like the sprockets are misaligned when the measuring tool itself is the problem.
Before you can clamp the rod on the front pulley face, you will need to make sure the engine and transmission have been aligned and locked down.
STEP 1: MAKE SURE THE ENGINE AND TRANSMISSION ARE SECURE
Before checking sprocket alignment, make sure the engine and transmission are properly installed, aligned, and securely fastened in their final positions. This is particularly important on custom motorcycles, where engine and transmission positioning can affect the chain alignment.
Tim’s engine and transmission are already bolted into the frame. He used the inner primary case to properly align and secure both components, then removed it for this tutorial. This provides a stable reference point for the alignment process. Do not make final sprocket alignment adjustments until the engine and transmission are fully positioned and secured.
Using some simple clamps, clamp the rod gauge to the face of the front sprocket. This is a fixed point and makes it easy to find alignment to the rear sprocket.
STEP 2: USE THE FRONT SPROCKET AS YOUR REFERENCE POINT
For this method, use the face of the transmission sprocket as the main reference point. Why? The rear wheel can be adjusted or repositioned within the frame, so its location alone doesn't necessarily tell you whether the sprockets are aligned with each other. The transmission sprocket provides a fixed reference when the engine and transmission are securely installed.
Position the straight rod against the face of the front sprocket and use small clamps to hold it in place. Extend the rod toward the rear sprocket to see how the two sprocket faces line up. Make sure the rod is held securely and isn't being twisted or pushed out of position by the clamps.
Be sure your rear wheel is straight in the axle plates and centered in the frame. You can check that it sitting even by measuring from the middle of the axle to a fixed point on the frame. The fixed point on the frame must be the same on both sides to ensure accuracy.
In this instance the rod is actually pushing on the rear sprocket meaning it is actually sitting further out and the sprocket needs to come in some. Tim currently has a dished sprocket on the wheel.
STEP 3: INSPECT THE GAP BETWEEN THE ROD AND REAR SPROCKET
With the rod secured to the front sprocket, inspect how it meets or doesn't meet the rear sprocket.
Look for a consistent relationship between the rod and the rear sprocket face. A noticeable gap on one side can indicate that the sprockets aren't aligned in the same plane. You can also use calipers to measure the gap between the alignment rod and the rear sprocket. This provides a more precise measurement of the offset that needs to be corrected.
In Tim's case the rod is actually pushing onto the dished sprocket meaning the main sprocket is sitting too far out and not aligned.
Another scenario is the rod can also push against the rear sprocket face which is what is happening on Tim's project. This means the rear sprocket is too far out and needs to move in. In the photo above you can see he has a dished sprocket and that is most likely not the right solution for this to align.
Remember that the alignment rod must be straight, and the front sprocket must provide a reliable reference. Otherwise, the measurements won't accurately represent the chain line. The goal is to have the front and rear sprockets properly aligned so the chain can run straight between them.
1/8" sprocket spacer and a flat main drive sprocket will pull it in the alignment ever so slightly which is what this bike will need.
STEP 4: UNDERSTANDING SPROCKET OFFSETS AND SPACER OPTIONS
If your motorcycle sprockets aren't aligned, there are several ways to correct the chain line. The right solution depends on your motorcycle, wheel configuration, sprocket design, and existing drivetrain components.
FLAT SPROCKET VS. DISHED SPROCKETS
A flat sprocket has a relatively flat profile, while a dished sprocket incorporates an offset into its shape. That built-in offset can move the sprocket inward or outward relative to its mounting surface, depending on the sprocket design and installation orientation.
Swapping between flat and dished sprockets can help bring the front and rear sprockets into alignment without requiring major changes to the wheel or drivetrain.
OFFSET FRONT SPROCKETS
Front sprockets are available with different offsets to accommodate different motorcycle configurations. The correct offset depends on your specific setup. Don't assume that a sprocket designed for a particular model year will automatically work with a motorcycle that has been modified.
Tim placing a 1/8" sprocket spacer onto the wheel.
SPROCKET SPACERS AND SHIMS
Spacers installed between the rear sprocket and its mounting flange can move the rear sprocket outward to fine-tune alignment.
Tim replaces the dished rear sprocket with a flat sprocket and adds an 1/8-inch spacer between the sprocket and the wheel hub flange. This small adjustment brings the rear sprocket into alignment with the front sprocket.
Lowbrow Customs offers 1/8" and 1/16" sprocket and pulley spacers for compatible wheel setups, including versions for early and later disc brake wheels.
When using sprocket spacers always verify there is still enough flange for the sprocket to ride on.
When installing a spacer, make sure the sprocket remains properly located and centered on its mounting flange. The mounting lip must still engage as intended, and the sprocket must seat securely. Always verify spacer compatibility, fastener engagement, and mounting requirements for your specific wheel and sprocket combination.
With the new combo of the 1/8" sprocket spacer and a flat main sprocket, the alignment is perfect.
STEP 5: RECHECK ALIGNMENT AFTER MAKING ADJUSTMENTS
After changing the rear sprocket or installing a spacer, reinstall and secure the components according to the torque specs. Position the wheel and then repeat the alignment check again with the straight rod.
In Tim's example, adding the 1/8-inch spacer under the flat rear sprocket brings the sprocket faces perfectly into alignment. The rod sits evenly against the face of the front sprocket and rear sprocket surfaces, without the noticeable gap or pushing as seen in the initial check.
Looks perfect!
WHAT IF THE SPROCKETS STILL WON'T ALIGN?
Sometimes, swapping a sprocket or adding a spacer isn't enough. Custom motorcycles can have unusual combinations of wheels, hubs, transmissions, and aftermarket components that require additional adjustments. If the basic corrections don't solve the problem, consider the following options.
TRY A DIFFERENT SPROCKET COMBINATION
Revisit the available sprockets and spacers. Pay attention to the various choices for front sprocket offsets, flat or dished rear sprocket options, and compatible spacers. The right combination may correct the chain line without requiring changes to the wheel assembly.
Lowbrow Customs rear sprocket with locking tab washer.
ADJUST THE REAR WHEEL SPACERS
In some cases, changing the rear wheel's position within the frame can help bring the rear sprocket into alignment. Modifying the left-side wheel spacer may allow the hub to move inward or outward. However, this requires compensating adjustments to the spacer on the opposite side to maintain proper wheel positioning.
This also may require the rear hub to be adjusted. If the hub position is changed, the rim may need to be repositioned relative to the hub to maintain proper wheel alignment. This can involve adjusting spoke tension and truing the wheel. Also this is very slight movement, not something to get a huge change out of.
These modifications should be handled by someone experienced with wheel building and truing. Do not machine spacers or modify a wheel assembly without confirming the correct dimensions and ensuring the finished assembly remains structurally sound. For most setups, sprocket selection and properly fitted spacers should be investigated before making more extensive wheel modifications.
Stock Sportster, in need of a chain conversion kit. Always check alignment, them wheels might not be stock.
DOES A STOCK MOTORCYCLE NEED A CHAIN ALIGNMENT CHECK?
Yes. Checking sprocket alignment is worthwhile even if your motorcycle appears to be completely stock. A previous owner may have replaced the rear wheel with one from a different model year, installed aftermarket drivetrain components, or made changes that affect the chain line.
This is especially relevant when installing a chain conversion kit. A kit may be listed for your motorcycle's year and model, but a previously modified wheel or drivetrain can change the alignment requirements. Never assume that a motorcycle's appearance tells the whole story. Verify the chain line before riding.
Fully installed Chain conversion kit on a 2000 Sportster chop.
FINAL CHECKS BEFORE RIDING
Once the sprockets are aligned, complete the rest of the chain drive installation.
Before riding, verify that:
- The front and rear sprockets are properly aligned.
- The chain has the correct tension and adjustment.
- The rear wheel is correctly aligned in the frame.
- The sprockets, spacers, and fasteners are properly installed and secured.
- The chain clears surrounding components throughout its travel.
- The rear brake functions properly
Sprocket alignment is only one part of a safe chain drive installation. Correct chain tension, secure mounting, proper wheel alignment, and adequate clearance are equally important.
We have the right combo for you to align your change drive properly, with multiple size front and rear sprockets, with different offsets, and spacer kits.
FIND MOTORCYCLE SPROCKETS, SPACERS, AND CHAIN CONVERSION PARTS
Here at Lowbrow Customs we cary motorcycle parts and accessories to help get your custom build to the next level. Whether you're converting your belt to a chain drive, replacing a pulley or sprocket, or just fine-tuning we got you covered.
The bottom line: Proper chain drive alignment helps your motorcycle's chain and sprockets work together as intended. Take the time to measure, make the necessary adjustments, and verify your work before riding. It's a simple but important step that can help prevent premature drivetrain wear, save you costly mishaps, and avoid potentially dangerous situations.
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