Chain losing tension

[carbontub]

Hello, I am Prateek from Ashwa Racing (formula student team of R V College of Engineering, Bangalore,India)

We are currently facing issues with excessive chain slack. We have a Suzuki GSXR 600 coupled to a Drexler LSD via a DID 525VX chain.
Despite tensioning the chain initially by the right amount, the chain seems to be losing tension too quickly and tends to hit the engine. I am curious to know if anyone has previously faced such an issue.
Any inputs in this regard are highly appreciated.

[NickFavazzo]

Check the alignment (offset and twist) of the two sprockets, that could account for higher wear.
Otherwise, some stretch is normal, have you designed an adjustment mechanism/tensioner?

[Claude Rouelle]

Something is moving and nothing is rigid.

[carbontub]

We are using an eccentric tensioning mechanism

How much stretch is normal?
DID says 20-25mm slack at the centre is normal for bikes (which typically have a large centre distance between engine sprocket and drive sprocket).But for FSAE, centre distances are much smaller.

I suspect there isn't enough room for the chain to even stretch normally. (i.e even if the chain is slacking/stretching normally it starts touching the engine). This maybe due to the position of the final drive sprocket relative to the engine sprocket.

[carbontub]

@Claude

I was not quite able to apply your advice to our situation, everything is rigidly mounted. Could you please elaborate?

[NickFavazzo]

Determine the allowable stretch per link (commonly documented as for 10 links)

work out the total change in chain length from new to the disposal limit.

Ensure you have enough adjustment range to cover that. If is wearing too fast, alignment is out, either static or under load.

[BillCobb]

One or both sprockets may be incompatible with your chain link length or roller dimensions.

[carbontub]

Something is moving and nothing is rigid.

I hadn't noticed this previously, the metlock(metal locknut) holding the engine sprocket in place became very loose(could be opened by hand) a few runs after was torqued.

But I am still unable to put the facts together. How can loosening of the metlock explain the slack in the chain and what's causing the metlock to loosen in the first place?

[carbontub]

Determine the allowable stretch per link (commonly documented as for 10 links)

work out the total change in chain length from new to the disposal limit.

Ensure you have enough adjustment range to cover that. If is wearing too fast, alignment is out, either static or under load.

There is no stretch in the chain. We compared the chain with the remaining links by placing them side by side.1287

[NickFavazzo]

That's not the best way to measure chain stretch.

[Claude Rouelle]

Carbon tub,

Not worth to introduce yourself? Just a matter of courtesy. This is not a super market.

[NickFavazzo]

He did in his first post, could have included a little more info (course/discipline etc) but the basics are there.

CarbonTub, have you a photo of the diff/engine/chain area?

[carbontub]

@Claude, I did introduce myself in the very first post. In case you missed it, I'm Prateek from Ashwa Racing (formula Student team of RV College of Engineering, Bangalore, India).

[Claude Rouelle]

Prateek

My apologies. You DID introduce yourself in your first post. I am sorry.

I am so used to people leaving a signature at the bottom of their post and I am so used to Indian guys not often introducing themselves that I assumed that you did not introduce itself. I assumed.... I should have checked and I didn't.
That is an explanation but not an excuse. Again I apologize.

Basically what I am trying to say is:
- Nothing is rigid: The chain, the chassis, everything has some deflection resulting to acting forces and also temperature change, and there is often residual deflection.
Therefore the slack that you can have in the chain. That is especially true for a new chain or for, other example, a new throttle cable. There is some kind of "bending in" needed procedure.
Other illustration: When I was in F1 we learnt that we needed to calibrate the pushrod strain gauge only after either a few track laps or a few run on the 7 post rig.
We could see that after a few "bedding in", the strain gauge did not show the same results as the one we got after a first calibration on a brand new pushrod.
- Things are moving. That is a consequence of the previous consideration. How can you be sure that your engine and your diff are exactly, all the time, at the same relative position to each other? Can you exactly measured each cause and of the different compliance and residual compliance? I can't but I can measure the final results.

Will you be at Formula Bharat? If so, we can discuss your questions and my comments in details. In just 1 week.

[Charles Kaneb]

https://www.youtube.com/watch?v=LdN27HzoyO4
Like the song in that link, this discussion's missing something.

1) How does a chain go from its new length to its service limit? If it's by yielding, wouldn't you see massive differences in chain life between drivers and between track surfaces, including some cases where the chain fails immediately and others where the chain life is indefinite? Wouldn't you see large variations in link length on a used chain? How much force would it take to reach a shear stress of 1000 MPa in the pin going through the chain, which is 4.4mm diameter?
2) Hold a brand new chain sideways, next to a chain which is at the end of its life, so that they extend out like beams. What do you see? What does that tell you about the mechanism of failure? Why do you usually replace the aluminum sprockets at the same time as the steel chain?
3) Under the maximum load you calculate the chain is under during acceleration or braking, how much does your chain deflect? (NOTE: Think CAREFULLY about the safety precautions when you test this, you'll apply several kN and things can go flying if they aren't anchored properly)
4) Why do you need any slack at all in a chaindrive? Why wouldn't you just slide the engine forward, or differential back, until it's "tight" and clamp it down in that position?