Clutch noise

[Miller]

I have a yard kart I'm building for my grandson and I put a new clutch on it, up on a stand it doesn't make any noise but when it's under a load with someone on it it makes a bad grinding/ chatter noise going down the road. It's not a squeal like it needs oiled, I already oiled it making sure to get nothing in the clutch itself but that didn't help. If anyone could help me out I would appreciate it.

 

[Hellion]

Photos would help a great deal because trying to diagnose your issue without seeing it is like arcane wizardry.

Make sure your gear ratio is right, for one thing. You could be abusing the clutch on account of an improper gear ratio:

The sprocket on the engine and the one on the rear axle should have a ratio close to 1:6. This means for every tooth on the clutch there are six teeth on the rear sprocket. So if you count 10 teeth on the clutch there should be 60 teeth on the rear sprocket. (12 teeth on the clutch means a 72 teeth rear sprocket).

72 / 12 = 6, so 1:6 or 6:1 gives you a great gear ratio for a centrifugal clutch.

I copy/pasted the above from this article-- https://www.bmikarts.com/10-Things-about-Centrifugal-Clutch
The size of the driven tires will also effect your final drive ratio and whether the clutch can propel a kart with really large
tires or not.

Lots of variables and it is like rocket science...

 

[Miller]

Thank you very much, I'm new to all of it and that makes sense on what my problem is. I was just given a frame and I bought everything separately. I probably have it way off.

 

[madprofessor]

it makes a bad grinding/ chatter noise going down the road. It's not a squeal

I always immediately guess that "grinding/chattering" noise under load is not the clutch at all, but rather the chain skipping teeth around the sprockets. Chain may be tensioned fine when not moving, but under the motor power pulling on it, something usually moves or flexes to loosen the chain so it skips until you back off of the gas. Everything would then appear correct again. There's a half dozen and more reasons a kart can do that, and everyone on this forum can name you a few, and how to fix them.

 

[JimD]

All of the above are good points. Put the kart up on kart stand or elevate just the rear wheels and turn the wheel and see if you can hear the noise where the chain may be hitting or rubbing. What chain size are you using? #35, #41, #420, #40 Please don't tell me it is #428 chain because then you have a problem. You need a special clutch sprocket for #428 chain because the rollers are LARGE .330 versus the #41 @.306 #420 @.306, #40 @ .312. The sprockets on most American clutches are made for the smaller rollers. You have to order a special clutch sprocket for #428 chain because the roller cannot get all the way down into the valley of the sprocket.
If you have #35 chain which is NOT roller chain, it just beats the cr_p out of sprockets and your rear sprocket could be worn out.
A picture of the clutch is worth a 1,000 words and helps all of us what to look for.
Could be the axle bearings are shot. Pictures do help.

 

[madprofessor]

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