Chain slack

My '13 Owners Manual Says .31 - .51", I've never seen a chain spec for this tight. I then got a factory service manual and it states a much more realistic and believable number of 1.50 - 1.89". The only service manual I could find is for the 2008 but being that nothing has changed in this area I don't believe that the '08 is to be well over an inch and the '13 to be well under an inch.

Until I hear otherwise I'm going for the 1.5 - 1.89"

The low measurement is the distance between the swing arm and chain when pushing the chain up, not the slack amount. If you set it correctly the chain slack will be correct. It's different than normal slack measurements. Take another look at the illustration in the manual

DPete wrote:

The low measurement is the distance between the swing arm and chain when pushing the chain up, not the slack amount. If you set it correctly the chain slack will be correct. It's different than normal slack measurements. Take another look at the illustration in the manual

Thanks for the reply. I keep looking at the manual it looks like every SLACK set procedure I've seen on all bikes. The manual refers to it as "Slack' as well. Pushing up in the middle chain span and measuring deflection has always been the norm for me. I just cannot see it being any different in the manual, it clearly shows same to me. The Service Manual also refers to this as SLACK using the same phrase even.

A typical slack measurement is taken from pushing the chain up then pulling the chain down, the distance the chain travels is the slack amount. On the wr Yamaha has taken out the up and down measurement by using the swing arm as a reference so if you push up on the chain and it's within spec the total slack should be correct. Try it

DPete wrote:

A typical slack measurement is taken from pushing the chain up then pulling the chain down, the distance the chain travels is the slack amount. On the wr Yamaha has taken out the up and down measurement by using the swing arm as a reference so if you push up on the chain and it's within spec the total slack should be correct. Try it

Yep, this is exactly what I'm doing as I've been doing for 50 years on all bikes with chains. My point is simply that the owners manual has the same pic you posted but oddly states the "slack" should be 8-13mm and the service manual says it to be 48-58mm. I suspect that 13mm would be a disaster. I understand that you're saying that you don't use the distance from pushing down to pushing up, but only to pushing up. However, a decent chain will not be able to be pushed further down then its natural sag by another 40mm! Not even a rubber drive belt will stretch that much with you standing on it. The owners manual is simply misleading at best.

You are not understanding that the 8-13mm is the distance from the swing arm to the chain when pushed upward, not a slack measurement. Good luck, I've done my best to clarify.