Stumped

[Mud2moab]

Customer brought me an

Manco American Cruiser 425B-69​

They just bought it for thier son for Christmas, and when the dad rode it the clutch burned up. I replaced the clutch with a Hilliard extreme duty, and my neighbors son went for a test ride it started smoking right away.
The cart has a 212 Predator engine. It has a 12 tooth drive sprocket and a 36 tooth driven sprocket.
What an I missing here.

 

[karl]

Gear ratio way off. It should look something like this. Help us help you by sharing a picture,
I suspect a previous owner has changed the axle sprocket to the way to small 36t, or put bigger tires on the kart than factory, or both.

 

[Functional Artist]

Gear ratio way off. It should look something like this. Help us help you by sharing a picture,
I suspect a previous owner has changed the axle sprocket to the way to small 36t, or put bigger tires on the kart than factory, or both.

Yup, what he said

Look around, the driven sprocket (the sprocket on the axle) on most karts is much bigger
...something like ~72T
...which would be a (6:1) gear ratio (72/12 = 6)

 

[Mud2moab]

The driven sprocket barely fits in the cover.
I'm not sure if the tires are to big or not.

 

[karl]

Picture time please.

Or simply just read the text on the rear tires, and relay what size they are.

Only other possibility other that gear ratio or tire size is the RPM of the engine is too low to fully engage the clutch.

But you said the driven sprocket is only 36t, that is clearly too small, and I picture i posted is
how your exact model kart should look, with a much bigger axle sprocket, so again picture please
if you want to solve your customers problems.

 

[Mud2moab]

In the morning when I get to the shop I will take pictures, check tire diameter, and engine rmp, and get back with you.

I appreciate your help.

 

[Mud2moab]

Good morning,
Here is what I'm working with.
It idles around 1300 rmp, and the top end rpm is around 4200.
The tire are 14" dia.

 

[karl]

Good news, thats the factory tire size, no problems there. About 15in tall is the size limit
for using a centrifugal clutch. And the engine rpm is good.

Bad news, some one swapped the axle sprocket to that 36t in an attempt to make the kart faster.

So right now, with your clutchs engagement speed of 2400rpm, the clutch will not stop
slipping until the kart is moving at 33+mph. Any speed below 33mph is cooking the clutch.
That will burn them up very fast.

These clutchs only can cool down when they lock up and stop slipping. They don't
like slow driving, either go or no go.

So the solution is to change the axle sprocket to 72 tooth. The clutch then will lock up
at 17mph, so whenever the kart goes above 17mph, the clutch can cool down.
The kart will have a top speed of about 26mph.

So if your customer wants this fixed, start soaking all the axle components in penetrating oil,
and hope it all comes apart easy to change that sprocket.

 

[Mud2moab]

Thank you,
I appreciate the help.

 

[madprofessor]

If you have to slide everything off of the axle on one side (bearing, any locking collars that aren't double-split, brake disc, sprocket, etc., don't ever do it again trying to determine the right number of teeth that you need for a larger gear ratio that doesn't melt clutches.
Use a sprocket hub with split sprockets that change out in 5 minutes for less than $20 each. Just use a quality chain breaker to adjust chain length beyond what the kart's adjustment allows. Examples below..............
Unihub - Sprocket Hub | AZ2556 | Azusa 2556 | BMI Karts And Parts
#35 Split Sprocket | 6335** | BMI Karts And Parts
WMS Deluxe Chain Breaker (#35, #41, or #40) | BMI Karts And Parts

 

[karl]

Mad relax with the split sprockets , 6 to 1 is the factory gear ratio for the kart. There's no guess work involved.

And there is not room for a sprocket bigger than 72t , at least enough to make any difference.

And it's not even his kart. All the OP needs to do it revert it to factory and he will have a happy customer.

Plus if the customer wants to upgrade, there is always the option of adding a 30 series Tav2 torque converter kit.

By the way, have you got your kart above 30mph yet?

 

[Mud2moab]

If you have to slide everything off of the axle on one side (bearing, any locking collars that aren't double-split, brake disc, sprocket, etc., don't ever do it again trying to determine the right number of teeth that you need for a larger gear ratio that doesn't melt clutches.
Use a sprocket hub with split sprockets that change out in 5 minutes for less than $20 each. Just use a quality chain breaker to adjust chain length beyond what the kart's adjustment allows. Examples below..............
Unihub - Sprocket Hub | AZ2556 | Azusa 2556 | BMI Karts And Parts
#35 Split Sprocket | 6335** | BMI Karts And Parts
WMS Deluxe Chain Breaker (#35, #41, or #40) | BMI Karts And Parts

The current brake hub and sprocket is a 1 piece unit.
I found a brake hub, a sprocket, and an adapter hub from BMI.
I'm hoping that will fit in easily, and that the parts ship quick.
The parents bought this for a Christmas gift.
I need one of the bearings a 1635 2RS with a ring groove, and can't seem to locate one.

 

[Denny]

Go Power Sports usually has that style of bearing in stock. They are in Keller Texas.

 

[Mud2moab]

Go Power Sports usually has that style of bearing in stock. They are in Keller Texas.

Thank you I'll try them

 

[Mud2moab]

Good news, thats the factory tire size, no problems there. About 15in tall is the size limit
for using a centrifugal clutch. And the engine rpm is good.

Bad news, some one swapped the axle sprocket to that 36t in an attempt to make the kart faster.

So right now, with your clutchs engagement speed of 2400rpm, the clutch will not stop
slipping until the kart is moving at 33+mph. Any speed below 33mph is cooking the clutch.
That will burn them up very fast.

These clutchs only can cool down when they lock up and stop slipping. They don't
like slow driving, either go or no go.

So the solution is to change the axle sprocket to 72 tooth. The clutch then will lock up
at 17mph, so whenever the kart goes above 17mph, the clutch can cool down.
The kart will have a top speed of about 26mph.

So if your customer wants this fixed, start soaking all the axle components in penetrating oil,
and hope it all comes apart easy to change that sprocket.

How well will a 12 tooth / 60 tooth work on this cart?
Anything larger the the 60t won't clear the frame.

 

[panchothedog]

A 60 tooth sprocket will certainly be better than a 36, but it is still border line.
Especially with 14" tires . Not trying to coax anyone into spending money, but can you find a clutch with a 10 tooth sprocket? Looks like the rims are 6" .You could probably find shorter tires in that rim size. At a gear ratio of 5 o 1,
12 x 60 teeth, even if it works a bit at first, the clutch will not have a long life turning 14" tires .

 

[panchothedog]

A torque converter would solve all the problems and would be cheaper than replacing the rear tires and probably not much more than a new clutch.
Impossible to tell from your pictures if there is enough room to install one.
Plus a bigger job and labor bill from you. Just trying to point out another avenue to cure the problem.

 

[Mud2moab]

A 60 tooth sprocket will certainly be better than a 36, but it is still border line.
Especially with 14" tires . Not trying to coax anyone into spending money, but can you find a clutch with a 10 tooth sprocket? Looks like the rims are 6" .You could probably find shorter tires in that rim size. At a gear ratio of 5 o 1,
12 x 60 teeth, even if it works a bit at first, the clutch will not have a long life turning 14" tires .

Thank you for all of your help. I found a 10t max torq, and ordered it.
It's really great to find such a wealth of knowledge on a subject, and the willingness to share it.
Bless you all, and have a Merry Christmas.

 

[JimD]

Forget the clutch for a tire size that big. 15" is too large for a clutch to move with the 1/6 gear ratio (for every tooth on the clutch there has to be 6 teeth on the rear sprocket- minimum). The only time the clutch will work for you is if you live on the top of a hill and you are going down the hill, it will NOT get you back up the hill. Kart builders used a 12 " tire with a 10 tooth clutch and a 60 tooth rear sprocket in the #420 chain and Manco when they used a #35 chain they used a 12 tooth clutch and a 72 tooth rear sprocket. We provided the clutches to all the kart builders and Comet provided most of the torque converters. We supplied t/c to only 1/3 of the kart builders the rest liked the bolt on series 30 which was was designed for mini-bikes but could be used on go karts. The reason the cover guards had so many holes in it was because a series 30 gets much hotter on the belt than a series 20 because it is forcing the belt up the flat side of the t/c. A series 20 when inboard mounted work in unison, as the driver moves inward and up the driven moves inward and down that is why they are much better on belt wear. All t/c on snowmobiles and golf karts are inboard mounted.