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How To Adjust The Primary Chain On A
Harley-Davidson Evolution Motorcycle          

The Harley-Davidson Motor Company produced the Evolution engines from 1984 through the early 2000s, offering a Big Twin Evolution engine as well as a Sportster Evolution engine.  These are great engines, and very low-maintenance, with hydraulic valve lifters, which mean you never need to do a valve adjustment.  The one thing you do need to adjust from time to time is the primary chain tension.  It sounds somewhat intimidating to a new Harley motorcycle owner, but learning how to inspect and adjust the primary chain tension on your motorcycle is very easy to do.  I've made 2 videos showing what it looks like to adjust the primary chain on an Evolution Big Twin (My 1991 FXLR Low Rider) as well as how to adjust the primary chain tension on an Evolution Sportster engine (My 2001 Buell Cyclone).  The videos are below, and I'll also include some step-by-step written instructions down the page below the videos.  I hope this helps you keep your Harley on the road and running right. 

How to adjust the Primary Chain on a Harley-Davidson Evolution Big Twin Motorcycle Engine.

How to adjust the Primary Chain on a Harley-Davidson Evolution Sportster Motorcycle Engine

As you can see in the videos above, to check the primary chain tension on your Harley, you need to remove an inspection cover, which has a reusable rubber gasket.  With the cover off and the transmission in neutral, you push up on the chain and measure how far the chain moves when you push up on it.  For a big twin it should be 5/8 to 7/8 inch (16 - 22 mm) when the engine is cold, and for a Sportster it should be 3/8 to 1/2 inch (9.5 - 12.7 mm) when the engine is cold.  This measurement is for the TIGHTEST section of the chain, and chains do sometimes wear unevenly and get stretched in places.  For this reason, you should rotate the chain 5 or more times and re-check the adjustment to find the tightest spot in the chain before doing any adjusting. 

To adjust the primary chain tension on a Harley-Davidson Big Twin, loosen the nut you see facing you through the inspection hole, and raise the plastic shoe until the chain tension is correct.  To adjust the primary chain tension on a Sportster, loosen the lock nut on the adjuster on the bottom of the primary case, then turn the primary adjustment bolt clockwise with an Allen wrench to increase the tension and remove slack from the chain.  Retighten the lock nut when you have reached the desired tension, and check it one more time before replacing the inspection cover. 

These chains don't stretch much if the engine is kept stock or near stock, so in most cases you'll just check it every 5,000 miles and won't need to adjust it, but it's good to know that when it is time to adjust the chain it's a simple process you can do yourself.