Timing Chain

[Murrays]

How tight should the timing chain be and at what point should I tighten it? Any tricks or advice that you veterans would care to pass along?

-murray

[shutterbiker]

murray,

i believe that co-motion has that information on their website. it is also available on park tools'
website. i believe the timing chain should have about 1/2inch of deflection in the center, but i
could be wrong.

steve

[Murrays]

i believe that co-motion has that information on their website.

Yeah, I read Co-Motion's info, but I thought I would ask for other opinions. Thanks for the Park advice, I'll go there too.

-murray

[TandemGeek]

Yup. 1/2" is about the norm, measured by lifting the upper run of the chain. Too loose only becomes a problem if you hammer hard enough to throw the chain off at the stoker's ring while sprinting or from being knocked around while riding on rugged terrain, e.g., unimproved roads and off-road. Of course, the aesthetics of a sagging timing chain are what drive me nuts.

Some additional fodder on timing chains:
http://www.bikeforums.net/showthread.php?s=&threadid=32267

Flipping over chain rings:
http://www.bikeforums.net/showthread.php?s=&threadid=33866

Also some stuff on crank phasing and eccentrics:
http://www.bikeforums.net/showthread.php?s=&threadid=33892

[zonatandem]

That's correct: 'bout 1/2 inch or a tad more deflection dead center.
Have actually broken a couple timing chains in our 'younger days' . . . stoker would of course be able to 'save' the ride by pedaling, while captain just steered (that's why the Brits refer to captains as 'steersman.').
Eccentric adjustment or new chain (well actually about a chain-and-a-half) will solve the problem.

[stapfam]

One thing to remember when adjusting the timing chain, unless you have spent a great deal of time trueing the two sprockets on the crank arms, there will always be a tight and a loose spot on the chain. Always adjust for the 1/2" deflection to be at the tight spot. Either I am lucky, or I had more time on my hands to set up the two sprockets, but I have 1/2" deflection at the tight spot, and only 3/4" at the loose spot. Other point to remember is that a new chain will stretch, so adjust on the concentric every 100 or so miles until it beds in.

[tornadobass]

One thing to remember when adjusting the timing chain, unless you have spent a great deal of time trueing the two sprockets on the crank arms, there will always be a tight and a loose spot on the chain. Always adjust for the 1/2" deflection to be at the tight spot. Either I am lucky, or I had more time on my hands to set up the two sprockets, but I have 1/2" deflection at the tight spot, and only 3/4" at the loose spot. Other point to remember is that a new chain will stretch, so adjust on the concentric every 100 or so miles until it beds in.

I tried adjusting a timing chain for the first time last night had found the opposite experience. At the tight spot, it could be tight, while at the loose spots, it had 3/4" of slack. I wasn't sure how to get that right considering how loose the loose spots would be with 1/2" slack in the tight spots. I'll probably need to do the routine with loosening the two chainrings and tapping on the chain until it evens out more.

Another helpful way of checking the chain adjustment is to drop the rear chain on the stoker's crank and feel for even and free rotation of the cranks through 360 degrees.