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KONA UNIT chain tension help

3K views 12 replies 6 participants last post by  NordieBoy 
#1 ·
Hi Bikers
I have a new unit and the chain tension varies massively from tight to loose
during each rotation of the cranks.
My bike shop cant fix it, they have had three goes.
Does anyone have any experience with this ?
Any other unit owners with the same or no problem ?
I would really appreciate some help.
Cheers
Jeff
 
#6 ·
Straight edge held on the seat tube to out near the chainring teeth and turn the cranks to check if the chainring is properly circular.
Similar with the rear cog.
My Unit with XT cranks and an oval ring is tighter on the left power stroke.
The chainring holes on the cranks are slightly out of spec.
 
#7 ·
Which cranks do you have? In my experience, most cranks are not completely concentric, and race face with the cinch mount are the worst.

You can remove your chain and spin the crank while watching the ring against the seat tube for high/low spots.

If your ring is bolted, you can follow Sheldon Brown's procedure for centering chain rings.

This relatively common though, and I would just run my chain a bit tight in the tight spots if I couldn't improve it at all.
 
#10 ·
This is very common on most singlespeeds (and also present on most geared bikes but nobody notices because of the derailleur). Manufacturing imperfections on the crank, spider, chainring, cog, etc. cause a tight and loose spot in the crank rotation.

Just set your chain based on the tight spot and ride it. You can try to get rid of it a little by moving the chainring (assuming a 4 bolt), but it should not cause any issues and you won't notice it.

Many of us run an oval chainring which also causes a tight and loose spot every rotation. It's not a problem and works just fine.
 
#12 ·
Hi.

I had exactly same problem with my kona unit 2018.
Front chainring is not centered correcly on FSA Comet Modular crankset. Mine had few millimeters ofset. You need special tool(expensive) to remove chainring and try to center it.
OR better...buy differend brand crankset with 4 bolt chainring attachment.
I used:
Shimano
SLX 11-speed Crank FC-M7000-1 175mm
SLX 11-speed Chainring SM-CRM70 32T for FC-M7000-1
XT Hollowtech II Bottom Bracket BB-MT800
But you need also 11 speed chain and 11 speed compatible rear Sprocket.
 
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