2021 750 GS factory lowered - CHAIN SAG adjustment questions

Greetings,

After 73,000 miles on my 2002 R1200C (shaft drive), I have moved on to a 2021 750GS (lowered). This is my third bike but the first with a chain. My bike was slightly used when I purchased it (521 miles) and I now have 1,675 miles on it. It had its 600 mile service done by the BMW dealer just before I picked it up.

I have read through the post by "drneo66" titled "F-Twins Tech - F650/700/800 - Setting Proper Chain Tension." This is a great post but I still had questions. I went to YouTube and watched several videos. This resulted in more questions.

1. Why would the chain sag CHANGE as the rear tire is rolled forward or backward? ("find the spot with the lowest sag")
2. Why must the measurement be done on the side stand? (I have installed an SW-motech center stand). Since the chain is on the low side of the bike, this makes reading the measurement awkward.
3. Most of the YouTube videos suggest that before measuring the sag I should shift the bike into 1st and roll forward to engage the chain. True? This seems to reduce the chain sag....
3. So, assuming I measure the chain sag while on the side stand, do I make the adjustments while on the center stand so that the axle doesn't have different forces on each side? (if leaned over on the side stand, doesn't that affect the wheel position on the axle if the axle nut is loose?)

4. When I have the bike on the center stand and rotate the rear tire, the chain periodically rubs the edge of the catalytic converter. I do not hear any rubbing when I "paddle walk" the bike in neutral (engine off). There is a slight wear mark where the chain ribs the cat. Is this something I need to address right away with a BMW dealer?

I look forward to hearing the advice of others.
Thank you!
Cindy

Welcome to the forum! I'm glad you found drneo66's thread on chain tension...I was going to send you there but you found it. I was hoping that would provide some insight. Hopefully some owners with more experience will stop by.

20774 said:

Welcome to the forum! I'm glad you found drneo66's thread on chain tension...I was going to send you there but you found it. I was hoping that would provide some insight. Hopefully some owners with more experience will stop by.

Click to expand...

Thanks, I'm hopeful that I will get some great guidance!

Welcome to the forum!
Chain stretch is frequently not linear. This means if a rider, for example, like to pull “hole-shots” and the sudden transfer of power to the rear wheels can create more “stretch” in one part along the length of the chain. “Sag” also changes as the bike is loaded- rider, accessories, gear as the wheelbase changes (slightly).
If you just ride the bike I think chain concerns are minimal. If you ride the bike “hooligan” style, you may have to pay a little more attention to it.
I don’t know what to say about the rubbing other than keep an eye on it.
With leather work gloves on, a rag dampened with WD-40 can give the chain a clean up if it gets the “fuzzies”. I like Chain-Wax for a little lube and rust protection. These bikes have O-Ring chains and are really sealed and lubricated. It doesn’t hurt to have a look once in a while.
No need for real concerns. Chains and belts built the industrial revolution
Gary

Thanks, Gary. I DEFINITELY do NOT ride like a Hooligan!
I see what you mean -- that the chain could be "abused" in areas.
Unfortunately, I am one of those people who TRIES to get everything "just so." ...so I am trying to do things properly with the bike. (a place for everything and everything in its place, as specified.... except for my desk--- it is a MESS!)

Thanks again,
Cindy

My experience with the F750GS as well as the F850GS is they both have larger than usual sag criteria. Perhaps because they are "off-road" capable. However, not only are the gap specs larger than street machines I've had, they are somewhat difficult to measure as the rubber chain guard on the swing arm makes it difficult to extend chain over full range. I think you'll find measuring and adjusting on the recommended side stand will give you better results and actually make it easier to find the right gap. Anther aspect of these bikes is getting use to the chain slap sounds on uneven surfaces even when correctly adjusted...as well as the significant tire noise for first couple of thousand miles or so. I did like the engine.

MotoDan, thanks for your reply.