Do you know anyone who has experienced catastrophic bearing failure inside the primary chain case of their 2007 or up Harley Davidson? Maybe they lost a clutch, transmission, or even engine crankcase bearing? Well I do. In fact this has happened to virtually everyone I know who owns a 30,000 mile or up HD built within these years. This has become an extremely common problem as of late, but fortunately there is also a very inexpensive fix as well. Before I get into that however, it seems important to first define the problem; for in truth it is a rather simple one. There is a cure for the Harley primary auto adjuster blues.
In 2006, Harley-Davidson engineers designed a primary chain auto-adjuster. This auto-adjuster was installed that year on Dyna’s, and starting in 2007 on the rest of the v-twin fleet.Now in theory, the auto adjuster is a step forward. Like its predecessor, the auto adjuster consists of a nylon shoe that applies pressure to the primary chain to keep it reasonably taught. In order to take up the slack as the chain stretches, a ratcheting system was developed that ratchets up the adjuster shoe as needed. Sounds good in theory, but there is a problem.
Anyone who has ever ridden a shovel or older Harley, those with a chain drive to the rear tire, knows that chains do not stretch evenly. As our rear chain wore, we would frequently have sections of the chain that were unduly slack, while other sections that were way too tight. Additionally, chains will also change tension as they heat up. Well, the primary chain is no different.
With that in mind, picture a loose section of the primary chain in which the auto adjuster ratchets up to take up the slack. Now introduce the tight section of the primary chain, but the auto adjuster cannot loosen up. This is where the problem lies. The design of the Harley-Davidson primary chain auto adjuster only allows it to tighten the primary chain as it ratchets up to take the excess slack from the primary chain. This design cannot loosen up, it can only get tighter.
You can imagine how this plays out. Not only does your primary sound like a freight train is roaring through your primary case, but the undue pressure on your primary drive chain is notorious for causing transmission bearing failure, as well as crankcase bearing failure, and even transmission spline destruction. In short, the auto adjuster will cause premature wear on your beloved Harley-Davidson’s primary drive system.
The M6 Primary Chain Tensioner makes a smoother ride by reducing annoying vibration, by keeping constant and correct tension at all times. Your transmission will ‘click’ into gear instead of ‘clunk’. It also improves shifting performance while extending the life of your primary chain. You’ll swear you just rebuilt your clutch and transmission.
When I researched the problems associated with the auto adjuster, I found only a very few alternatives. The Hayden M6 was the product that had been out there the longest, and had the most positive comments about it on the internet. Enough trial and error, I decided to go with what has been working for 25 years. I chose the Hayden M6 BT07.
Hayden Enterprises states, “The M6 automatically adjusts the primary chain on Big Twin Harley-Davidsons from 1965 to present. Now you can have the proper chain tension during acceleration and deceleration with the benefit of smoother shifting and less vibration. Riding with an M6 installed, your transmission will ‘click’ into gear instead of ‘clunk’. You will swear you just rebuilt your clutch and transmission. Reliable and practically maintenance free, the M6 delivers a noticeably smoother ride.” I have to concur!
If you could do only one modification to improve the performance and durability of your twin cam Harley-Davidson, I would highly recommend that you look into the Hayden M6 BT07.Boyd Cycles has them in stock and ready to go. You too will be so impressed by the overall quiet and smoothness of your primary drive system, you might just think you rebuilt the transmission.