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Offline Danno

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Unable to measure chain sag correctly
« on: June 05, 2020, 03:02:12 AM »
One aspect I find annoying on these bikes is measuring chain sag.  I can't get a good measurement because the chain hits swing arm chain guard before it fully expands.  I'm at  1 1/2 inch sag when chain contacts guard.  It is obvious the chain will go higher, but can't.  So how does one get a true measurement? 

Offline ab8mi

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Re: Unable to measure chain sag correctly
« Reply #1 on: June 05, 2020, 04:44:36 AM »
I have not had that issue as mine does not hit guard and I can get a correct measurement, using the side stand, also should mention that I have the lowered version.
Racing Red BMW 850 GS

Offline KSD

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Re: Unable to measure chain sag correctly
« Reply #2 on: June 05, 2020, 08:48:02 AM »
Yes, you are right, that's how it is. According to the instructions, the measurement should be done on the side stand, and then it is difficult to assess the upper tension limit (because as you wrote, the chain hits swing arm before it fully expands).

The solution is to focus on the lower limit (ensuring the correct miniumum) and to add a light margin to up.

Online Matty589

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Re: Unable to measure chain sag correctly
« Reply #3 on: June 05, 2020, 11:28:01 AM »
Yes, I have encountered this too. I would add to err on the side of caution - a chain that is a touch too loose is better than a chain that is too tight. The other possibility is to measure sag a bit off the mid point and do a basic calculation to get mid point sag. IME if it requires adjustment then itís probably a quarter turn at the adjusters, no more. A little here makes a big difference to sag.

Offline KSD

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Re: Unable to measure chain sag correctly
« Reply #4 on: June 05, 2020, 02:27:35 PM »
*Originally Posted by Matty589 [+]
if it requires adjustment then itís probably a quarter turn at the adjusters, no more. A little here makes a big difference to sag.

Exactly. With a standard pull of the chain, a quarter of a turn is usually enough. I also wrote about it in this topic: https://www.850gs.com/index.php/topic,661.0.html After removing the wheel, there is a bit more work with setting the tension but it is not difficult either.

Offline MCMXCIVRS

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Re: Unable to measure chain sag correctly
« Reply #5 on: June 05, 2020, 02:43:48 PM »
I've found that if I can lift the lower chain up to just barely touch the swingarm without forcing it, its about the perfect amount slack.