I wanted to post this information in hopes that it'll help someone down the line.

I've been running a chain final on my FXDB for several years now and it's been very difficult to find information on proper tension, since the common application is on foreign bikes. I wouldn't necessarily call this information "definitive", but it's based on what I've found over the years and works for me.

For reference I am running a 530 chain with 24-tooth front sprocket and a 51-tooth rear. The approximate span from the center front sprocket to center rear sprocket is 22". According to Tsubaki Chain (7.1.2.1 Chain Slack) slack should be ~4% of the span. That slack recommendation is not motorcycle specific but matches what I've found over the years in other forums. The general recommendation I hear for Harley's is 1-1 1/4" slack. So, 4% of 22" is .88" and that gets us right where we need to be. The recommendation of 1 1/4" is too slack, I use 1 1/8" as my max which gets me back to ~1/4" beyond the spec of 4%. The end result is slack between 0.88 and 1.125 or 22.4mm and 28.6mm (I don't like the Metric system, but sometimes it's just easier).

I am measuring slack with the bike unladen on the jiffy stand. For reference, I found that the difference in slack with the bike unladen and my weight on it (~225lb) was only 1/8" less.

I am checking slack at the mid-point between the front and rear sprocket, pushing up on the chain with my finger from below with moderate pressure till movement stops. I am not using any measuring device to check pounds of upward pressure.

This information is based on my experience and equipment, use it with caution. I am not an expert or professional mechanic and take no responsibility for the application of this information.

 

That's some handy info.
Thanks for sharing, Snake.

 

Good info from Snake Eyes.

I adjusted plenty of chains on dirt bikes when I was younger. You gotta have slack to allow for swing arm travel and to not wear sprockets too quickly.

To err on the side of caution, a loose chain is better than a tight chain.


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