adding a jack shaft

[Doc Sprocket]

Do the jackshaft. You can always regear further on down the road, once your daughter gets used to everything and becomes Mario Andretti. That will let the kart grow with her, and the existing engine will have sufficient power for the future.

Buying a smaller engine will do nothing to limit her speed. They are all governed to 3600RPM out of the box. At lower gear ratios, the 2.5 will push jaus as hard (and fast) as a 6.5. The difference becomes apparent at higher ratios, where the 2.5 would run out of oomph, the 6.5 would keep pushing.

The jackshaft setup will better prepare the kart to serve her for the future, and solves the here and now. The smaller engine does neither.

I wouldn't mess with clutch arrangements, still likely to overheat and fail. Use gearing to control speed.

 

[shake this]

Thanks toystory, I knew I could find the best option here.

So my shopping list should include the jackshaft listed in the first post, a 10 tooth sprocket and a 17 tooth sprocket correct? Anything that I’m missing that I’ll need to pick up other then more chain? Think this should gear it down enough for her starting out or will it be to slow? If my calculations are correct a 10 and a 17 tooth sprocket should give me a 9.18:1 or about 13 mph. Should I step up to a 10 and 14 for a 7.56:1 ratio or about 16 mph?

How much chain do you think I should order? BMI is showing 70 link lengths for $10.00 but not sure if I should just order 1 or 2 and then some master links. It's a little harder to figure out length without having everything mocked up in place.

I hope this should be the last of the questions but don't want to rush into ordering stuff without making sure it's everything I need and will work together.

 

[Doc Sprocket]

The speed you gear for really is a matter of your opinion of your daughter's beginning ability, as well as the amount of available open space. For my 10- and 8- year olds' learning, I geared for 13MPH. Even at that speed, my 8-year-old was nervous.

I'm honestly not sure how you'd figure out how much chain you'd need without having the components in hand. I buy my chain in 10 foot lengths, which is always plenty.

 

[shake this]

Once again...thank you so much toystory.

Ordered all the parts today and look forward to setting it up this weekend. Decided to order both the 17 and 14 tooth sprockets. Figured I might as well have the 14 on hand for when she gets older and needs a "little" more speed. I'm excited to see how much heat this saves on the clutch. Just from using it this weekend, it seemed to have a little harder time taking off on an incline then when we first started riding it so I'm sure a little damage has already been done. I think the torque added by using the jackshaft will make up for this minor issue thou.

 

[Doc Sprocket]

It certainly will. When I did the shakedown testing on my kids' kart, the clutch was having no problem handling my weight and going up mild inclines. FWIW, I used a 4hp Kohler clone, a Comet 400 series centrifugal clutch, and geared at 12:1 with 15" measured diameter turf tires. I should also point out that it's a fairly heavy frame, too. If you use similar gearing, I see no issues for you.

A lovely little plus to the ultralow munchkin gearing is retarded amounts of torque at the wheel. No problem spitting out dirt and gravel. She might even become your "L'il Drifter"!

 

[shake this]

A lovely little plus to the ultralow munchkin gearing is retarded amounts of torque at the wheel. No problem spitting out dirt and gravel. She might even become your "L'il Drifter"!

She will need to find a job first to help pay for tires as I don't see them lasting long as is. LOL

Just thinkful that I decided to keep them all the same size on this kart, easy to rotate.