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Primary Drive: Adjustments need to be made

The Primary Drive : Attention Harley-Davidson owners. That big case on the left side needs opening periodically, and especially if it’s been a while.

Harley-Davidson primary service: Ya gotta do it. Yet, one of the jobs many owners are lax on is the primary drive; it does need some love once in a while. The oil needs to be changed once every couple of years or more often if you are a “high miler.” I am running an AIM (centrifugal) lock up clutch and am very happy with it. 

That said, it still has clutch plates and like all clutches the plates do wear some eventually. This wear builds up in the bottom of the case. IF it looks soft and organic it’s probably just clutch wear, which is expected. If you see metal, things could get expensive.  If you just pull the plug and change the oil, that sludge stays in the case. I think it’s best to pull the cover and then give it a good clean. This is an opportunity to look at everything else that’s in there. 

There will be a spec on acceptable plate thickness in your manual if you want to go so far as take the clutch apart. This is probably not needed unless you suspect a problem. One clue might be poor shifting or slippage; either case might be cured by a simple adjustment if you are lucky. (The best time to do it would be now.) 

One thing to remember about slippage is that it is sneaky; it can start off barely noticeable. The other thing is the primary tension adjustment. It’s easiest with the cover off, about half-inch to 5/8- inch of play unless you have an auto tensioner. Once again symptoms of a loose chain might be extra vibration or “clunky” shifting.   

I installed an M6 tensioner (Hayden Enterprises) a few years back. After getting it set up it still has not required any adjustment at all. It’s been a great addition to any older Harley. Much better shifting is provided and there is no need to adjust for years. Shims are provided if the chain wear gets to the point of needing them. That’s why the newer model Big Twins have their own version that comes stock. 

Also look at the starter pinion and its mate on the clutch hub—they can take some abuse especially if you are running a big-inch engine. The modern motorcycle oils all work fine but AIM recommends automatic transmission oil so I have been using it with no issues. There are clutch packs in the automatic transmission of your car, as well as a transmission filter, which is required to protect the hydraulic components. 

How do the sprockets and chain look? Putting it all together with new gaskets should mean you could forget about it for another year or two. A little tip on the gasket install: cut the heads off a couple of spare bolts and slot the ends then use them to “hang the gasket.” They can be easily removed and replaced with the real fasteners after the cover is on. 

by Rich Burgess Canadian Biker Issue #330


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