Chain Tension

[KwicK To Master KTM]

I am really struggling trying to understand the method for measuring the chain slack as per the owners manual - I do understand mm just thought I had better put that !

But in the owners manual it has a diagram showing to adjust the chain with 5 - 7 mm play but it is really had figure if they mean

5- 7 mm from the bottom of the swing arm when fully pushing the chain up or just 5-7 mm play general ??I have tried to search online but no luck.
Can anyone shed any light on this please ?

 

[TZMike]

I was confused about that too. 5-7mm is no where near enough fee play for a chain. But if you look closely at the sketch you can see they are referring to the clearance between the swingarm and the chain. But it's not clear if it is the top of the chain to the bottom of the swingarm, or the middle of the chain to the top of the web on the swingarm, or something else.

 

[KwicK To Master KTM]

Thanks TZ - At least now I will be closer to the ball park !

 

[Treachery]

There's an interesting article in Motorcyclist this month about Yamaha's chain tension recommendation on the FZ-09 (I think). Basically the magazine said Yamaha was FOS. With any weight on the bike, there was basically no slack, which can potentially damage the output shaft and sprocket, bearings on both ends, and interfere with suspension action. It sounds like one of those goofy old school rules of thumb, but if it looks too tight, it probably is.

 

[Texas250]

That seems way too tight. My CBR250 says 20-30mm.

 

[TZMike]

the KTM manual seems to refer to a gap of 5-7mm between the top of the bottom section of chain and the bottom of the swingarm (see pic above). I will probably ignore that suggestion and have 1.25-1.5 inch slack in my chain with the conventional method we all use. Of course I will check to make sure the chain is not binding at full rear suspension travel or hitting the bottom of the swingarm before riding out into the world...

 

[motoarch]

There's an interesting article in Motorcyclist this month about Yamaha's chain tension recommendation on the FZ-09 (I think). Basically the magazine said Yamaha was FOS. With any weight on the bike, there was basically no slack, which can potentially damage the output shaft and sprocket, bearings on both ends, and interfere with suspension action. It sounds like one of those goofy old school rules of thumb, but if it looks too tight, it probably is.

The last part is right but the first part looks like you got something backwards. With no weight on the suspention or at full travel you can damage things. That's why its allways better too lose then too tight.

 

[guzz46]

I had mine adjusted by the method used in the manual, and my chain was always noisy, I'm talking knocking noises when you spin the chain while on a paddock stand, I thought it must just be a cheap chain, but recently I added more slack to the chain, maybe about 30mm when sitting on the bike, and the noise went away.

 

[TZMike]

"full rear suspension travel" = fully compressed shock

Mike

 

[motoarch]

I always think of full travel as the maximum amount of compression available. So when you bike is on a stand it does not have max travel available because there is some compression due to the bikes weight. When the bike has no weight on the weight and therefor no compression on the shock it has full travel available. When the shock is full compressed there is no travel available so I guess it technically be at full travel. I never really thought about it till just now.

Anyway my point was when you have no compression you risk damaging drive components if your chain is too tight so loosen the damn thing.

 

[TZMike]

Went dirt bike riding with a few friends this weekend. Most of them have KTMs. They checked chain adjustment by pushing the bottom of the chain up towards the bottom of the swingarm and measuring the gap between the two just like the view shown in hte RC390 manual. Seems this is a standard method for KTM off-road bikes. Pretty simple really once I saw it done.