Chain Wear Eccentric Tensioner

[zephyrus17]

I'm designing the eccentric tensioner for our car this year running a Yamaha YZF-R6 engine, but I can't find any information on the 'magnitude' of chain elongation. It's a pretty situational thing, since good lubrication habits can reduce it to it's minimal. But does anyone have any data on the elongation with respect to distance run, for example? Then I can easily get the incremental angles to adjust the tensioner.

[rjwoods77]

Just plan for the worst case which is the chain has stretched enough that you need to get rid of a link. So whatever your chain pitch is which is typically a half inch. No data needed as it is a practical problem.

[Hector]

I'll add a quick note that the amount of adjustment you need to go from a slack chain to a properly tensioned chain is always, always less than you think. I know that 0.05" (~1.25 mm) is the difference between "wow that chain is slack" and "wow that chain is almost too tight" on our current 520 setup. Hope that helps.

[zephyrus17]

Thanks for the info. I've had a look around and it's about 5%.

To achieve the best accuracy in tension, It would be best to have 1 degree increments for every bolt hole that matches up with the tensioner carrier.

I could just drill a hole every 1 degree, but that would mean that my tensioner would have to be huge. So I'm thinking of drilling two row of holes at staggered angles on my tensioner and the carrier. For the tensioner, the top row would have holes at, say, every 5 degrees and the lower row every 7 degrees. This would be the same on the carrier, but slightly offset so that I can create 90 bolt matches from 0 to 90 degrees.

I remember there was a mathematical topic on this, but I forgot the name. I'm sorry if it sounds very vague and confusing. Does anyone have any ideas?

[Peter7307]

If a simple tensioner is all that is needed try a bolt with a lock nut and a spring.
Saves time , weight and does the job as well as any vernier set up (plates with various numbers of holes).

You might want to have a look in any motorbike showroom (the bikes are new and clean) at some chain drive bikes for alternative ideas.

Pete.

[zephyrus17]

So the spring rests around the thread of the bolt and the nut tighten to change the angle?

[Andy K]

Having designed one for our 2010 car, I can offer the following suggestion:
- get the finest hole resolution possible... the vernier concept applies here to reduce size. I had 3.3 deg adjustment and it was hit or miss as to getting the proper tension in the chain.

[Peter7307]

zephyrus17 , Basically Yes.
All you need is something simple and reliable and let's call a spade a digging implement here...this HAS been done before.
Have a look at a few that work for "inspiration" and put your time and efforts into something more challenging or interesting.

As AndyK said: Getting precise adjustment on an item which is continually wearing can be a huge cost in time resources and often a less than satisfactory outcome.

Just my 2c worth.

Pete.

[rjwoods77]

Having a spring loaded chain tensioner means you never have to worry about eccentrics and also it is nice to cushion drivetrain reverse loads. Those benefits aside they are a little bit of a hassle to setup right but once done you dont really have to worry about it. Also you can use the spring to set the desired pretension on the chain.

[Adambomb]

+1 on high resolution adjustment. Especially with the short chains we're running. We had a bit of runout in our sprocket one year, probably at most 0.005 in., which resulted in a chain that was zero-slack at one point in sprocket orientation, and something like 2+ inches of slack at the opposite end of rotation.

[zephyrus17]

I've calculated getting holes every 6 degrees on my tensioner and every 5 degrees on the carrier. That gives me +1 degree increments, but only around 60 degrees total rotation. Assuming 5% elongation as the limit, that means i'd have to get quite a large eccentricity on my tensioner for all 60 degrees to cover that 5% elongation