Chain Tension

[Jim Garry]

The chain tension on my 2002 Suzuki GSXR keeps loosening up during every event. Used to have a split sprocket so this winter it was replaced with a high quality one piece sprocket. The chain is also of good quality and brand new, as each chain at the start of every year has been.

The car is a Cheetah.

Does anyone have any suggestions on what might be going on?

Below are links to some Cheetahs found online to show the chain tension set up.
http://sports.racer.net/index1.html
http://sports.racer.net/images/chass...h_reuter_2.jpg
http://sports.racer.net/images/chass...h_reuter_3.jpg

Thanks,

[Jim Garry]

I'll add that this is an autocross-only car yet after less than 10 runs, the chain will be loose again.

[DaveW]

Just guessing, since I have no direct experience with chain drive:
1. I assume the adjuster is staying put, not slipping to cause slack
2. Wear is the next obvious suspect
.....a) Wear within the chain itself (roller-to-pin, link pivots, etc.) has the potential for the largest and fastest increase in chain length
.....b) Wear at the contact surfaces between the sprocket(s) and chain
.....c) Mismatch between chain and either or both drive and driven sprocket causing wear (low probability, since I'm sure these are matched)

So, unless the chain is (internally) wearing quickly, I would suspect a worn drive sprocket, causing a mismatch and rapid wear. I assume the drive sprocket is smaller (fewer teeth) than the driven, and it would therefore be the first place to suspect wear.

What I think may be happening is that when the teeth wear, they become narrower. Each time you tighten it up, you pull the rollers to the bottom of the tooth valley, and it is tight. However, with the wear, this would not last long as the rollers slip up the sides of the worn valley, stretching and wearing the chain, and becoming loose.

[David Ferguson]

We lube and adjust the chain on our Stohr P2 car pretty much after every session (20-30 minutes typically). Not sure your experience is abnormal.

Make sure you are only adjusting the chain based on the "tightest" spot. We use split sprockets and there is always one position of the rear sprocket that is the tightest. Overtightening the chain does seem to lead to more chain stretching, and more sprocket wear.

[john f]

If you think it is chain stretch, remove the chain after each event and measure the length!
You will either verify that it is chain stretch ( which most people would say it is) or you can start looking else where. Just my $0.02

john f

[Daryl DeArman]

You mention replacing the rear sprocket....

(a) What is the condition of the drive sprocket? They are usually much better quality than the axle sprocket but their very small diameter usually leads to accelerated wear (much faster than the rear sprocket would if the rear sprocket was same alloy).

(b) Is the thickness of the new rear sprocket the same as the old, perhaps it is not perfectly aligned with the drive sprocket causing accelerated sprocket wear.

(c)Looking at the condition of the tension adjustment slots and the size of the fasteners...maybe it is moving during a hard launch. Maybe an adjustable stop bolt on the top pivot would solve the issue.

(d)None of the above

[Jim Garry]

Thank you gentlemen. You've been very helpful.

[DaveW]

Thank you gentlemen. You've been very helpful.

You're welcome. Please let us know what you find.

[Daryl DeArman]

Please let us know. I'm curious as well.

[Jim Garry]

Not sure, but when I removed the rear sprocket (four days of autocross on it) and compared it with the even newer sprocket I just purchased (different brand), it looked like the first one was not as round as it should be. I'll be running the car this weekend and will let you all know if the chain tension issue improved.

Thanks for all the input.

[ReynardF1000]

Sprockets can create optical illusions. Until they have significant wear they can look both good and bad, for some reason. Measurements are the best means of determining wear.
Remember, the chain doesn't really "stretch". The bushings wear and create a long chain. The manufacturers website technical areas have great information on % of growth for life estimations. Research your chain.
Autocross gearing puts very high tensile loads on chains, wearing bushings quickly.

[Mike Devins]

Just a point of interest. One my rear sub frame we use shims to adjust the chain and adjustments of .005" to .010" are not uncommon. It does not take much wear to make the chain loose. If you have 40 bushings between the sprockets .0001" (one ten thousands) wear per bushing would need a .005 adjustment to get it back to where is was.

[Jim Garry]

Good information from the previous posts. Thanks very much.

On Sunday the car had 12 1/2 runs (caught up to a slower can and had to back off for a re-run). The chain tension at the end of the day was still good. No slap during the event. Much better than the other outings this season.

So changing the sprocket helped a lot. And the one that was taken out of service was brand new at the beginning of the year.

[DaveW]