Tech Talks: Adjusting your Primary Chain
A maintenance procedure that’s easier than you think
A Big Twin’s Powertrain is non-unitized design. That is, the gearbox is mounted separately from the engine, which means there’s need to connect the two in order to transfer power. That’s where the primary drive, found in that massive aluminum case next to the rider’s left foot, comes into play.
As the name suggests, the primary drive is the initial transfer point of power from the engine to, ultimately, the rear wheel. The reciprocating power that’s generated by the engine’s crankshaft is converted into rotating energy through the moving primary chain and sprockets that spin the transmission’s input shaft. Once the energy regroups inside the transmission it’s dispersed through the gears and into the secondary drive, which is the belt or chain drive that rotates the motorcycle rear wheel. This is a brief explanation of a Harley Davidson powertrain, and, as you can see, each component plays an integral part in moving you and your bagger down the highway.
Being that the powertrain consists of a series of moving parts, you’re going to have to make periodic adjustments to them so they will operate properly. Over time, moving parts, such as the primary drive’s sprockets and chain, wear out. As things wear, they require adjustment to maintain proper tolerance. And it’s the primary driver’s multi-row roller chain that needs to be inspected and adjusted on occasion. It’s a rather straight forward procedure, too, one that you can do in your own garage or shop.
We happened to photograph this primary chain inspection and adjustment sequence at one of the best places to retrieve information about a Big Twin engine, an authorized Harley Davidson dealership. In this case, the dealership is Anaheim Fullerton Harley Davidson, where this page will walk you through the procedure.
Most of the action takes place within the inspection window that is accessed by removing the plate held on by four bolts. You’ll need a ruler, even a simple plastic one like what you used in grade school will do, to make the measurements and few basic hand tools to perform the adjustments. To adjust, loosen the adjusting shoe’s 9/16” nut a few turns and move the shoe up to tighten the chain or down to loosen.
A great time to inspect and, if needed, adjust the primary chain is when you have to drain and replace the primary case oil. Harley Davidson recommends its multipurpose synthetic oil, but if you have a preferred brand that’s been developed for the primary drive, by all means, use it. Just make sure whatever lubricant you select is specifically for this purpose.
One the inspection plate is off; you have a good view of the chain’s rollers and the adjuster shoe, so use the time to visually inspect them for wear. Look at the chain’s rollers to see if they’re receiving full lubrication, and check the adjuster shoe for cracks and such. Inspecting and adjusting the primary chain doesn’t take long, and when you’re finished you’ll have one less component to worry about during your next long-distance ride. Just be sure to replace the inspection plate gasket.
Tools You’ll Need
- Pipe sealant
- Drain pan
- T27 Toex
- T40 Torx
- 9/16” socket (deep)
- Ratchet extension
1. Basic maintenance like adjusting the primary chain can be performed in your own garage or shop when it’s time to change the primary oil. Just make sure the bike is secured in an upright position when you begin.
2. The first thing to do is to drain the primary case of its old fluid. After placing a drain pan under the primary, use a T40 Torx to remove the drain plug that’s located just beneath the derby cover.
3. Allow the old primary fluid to drain into the pan. While it drains, you can inspect the primary chain to see if it needs adjustment.
4. Use a T27 Torx socket to remove the four bolts that hold the primary inspection plate in place. It’s wise to replace the inspection plate gasket before you install the plate.
5. With the inspection plate removed, you can inspect the chain’s rollers for wear. Try inspecting them for signs of deterioration. With the transmission in neutral, spin the engine a little bit several times so you can see the whole chain.
6. Measure the chain in several places and try to take two readings each time. One is with the chain’s top run at slack. For the other, he raises the ruler against the top run to remove the slack and measures again. The difference in the two at the chain’s tightest point is the chain’s slack.
7. Use a 9/16” deep socket to adjust the chain’s free play. With the chain cold, set the free play between ½” and 7/8”. Once you have retightened the nut, measure the slack again to make sure you have set the proper amount.
8. Since the inspection plate is open, also inspect the adjuster shoe that is pressing against the chain’s bottom run. You can see the adjustment nut in the upper right corner.
9. Unlike the engine and transmission drain plugs, there’s no O-ring on the primary case drain plug. To help seal it, wipe a dab of pipe sealant along the bottom edge of the bolt head.
10. After wiping all the oil from the primary cover, reinstall the primary case drain plug. Once it’s seated, gently torque the four inspection plate bolts and the derby cover bolts to 108 in-lbs.
11. You can now refill the primary case with fresh fluid. Most shops use lubricants from a common source instead of single-quart containers. Pump in 32 ounces of fluid. You need to add the proper amount for your year and model bike.
This year, bike runs are set to kick off from all over the country. A multitude of riders will be congregating for a week of festivity all sharing their love for bikes. There will be a lot of stories and building tips to share with new friends as you ride the days with the rally. Make sure to travel safe and wear the required safety gear like carbon fiber helmets. Good luck and have a wonderful ride.