adding a jack shaft

[shake this]

I'm building a red talon with a 5hp B&S engine for my 8 year old daughter.

I'm thinking it might need a jack shaft to slow it down until she gets a little older. How hard would it be to add one and could somone point me in the right direction in picking one out that would work on her kart?

I found this one but not sure if it would work. http://www.bmikarts.com/item/Clutch-Mount-with-Jackshaft-3708

It also seems I still need some more parts or I'm just not visualizing how it bolts up with the engine and drive wheel.

Thanks.

 

[rgvkid]

You can get the kit from BMI or from azusa engineering. They are all from azusa engineering. Check out T-mans Offroad Kart, Great design and he is always online to help you out. He built his for his lil girls. I just built a 3.5 for my girlfriends 7yr. old and it is alot quicker then i thought it would be. Im just putting an adjusting screw pedal stop so i can close the distance of the gas pedal when the kids are driving.

 

[devino246]

That jackshaft would be the best option if you cant weld. You'll also need 2 sprockets and some chain. Dont limit the speed by limiting the throttle, you'll tear up the clutch real quick.

 

[shake this]

I'm going to try a throttle stop first but a little worried that it won't allow the RPM's get up where the clutch needs them to fully engage.

I'm thinking I need to choke it down about half of what it's at now. This little engine has a little more pep then what I was expecting.

 

[shake this]

if you cant weld.

I can weld but don't have easy access to a welder at this time. Maybe I need to try and find a smaller engine for now.

 

[devino246]

I'm going to try a throttle stop first but a little worried that it won't allow the RPM's get up where the clutch needs them to fully engage.

I'm thinking I need to choke it down about half of what it's at now. This little engine has a little more pep then what I was expecting.

Well if idle is about 1800, and top is 3600, then the median would be 2700rpm. I wanna say full engagement is 2800, so your clutch would be slipping.

 

[devino246]

I can weld but don't have easy access to a welder at this time. Maybe I need to try and find a smaller engine for now.

That jackshaft does not require welding.

 

[shake this]

what about the extra sprockets or is everything built in?

 

[devino246]

what about the extra sprockets or is everything built in?

Extra sprockets slide on and are held in place with a set screw.

 

[shake this]

And by choosing the correct size sprockets, you can adjust your overall gear ratio correct?

I'm also assuming I'll need a chain from the clutch to the jack shaft and then from the jack shaft to the drive wheel.

If I have everything correct then this will work with my application with little if any modifications?

 

[devino246]

And by choosing the correct size sprockets, you can adjust your overall gear ratio correct?

I'm also assuming I'll need a chain from the clutch to the jack shaft and then from the jack shaft to the drive wheel.

If I have everything correct then this will work with my application with little if any modifications?

Got it right! Just remember that gear ratios are multiplied, so if you have a 12 on the engine and a 16 on the jackshaft, then a 12 on the jackshaft and a 60 on the axle, then you'd have a ratio of 6.66:1.

 

[robbie]

One thing you may not have thought of..... If the engine is in line with the wheel sprocket and you add a jack shaft, then you'll need to move something out of line so the jack shaft output will be in line with the wheel sprocket, and the engine will be lined up with the jack shaft input.

You'll have to move something.

 

[shake this]

What would be a good sprocket set if I have a 10 tooth on the engine and a 54 tooth on the drive wheel and say I wan't to cut the speed down to about half?

 

[robbie]

You could use any two gears where one has twice as many teeth as the other. For instance, 10 and 20, or 9 and 18.

If you buy from MFG Supply, they have a 9 tooth and a 17 tooth available for #40 chain (in case that's what you're using). That would cut the speed almost in half. Their website is http://www.mfgsupply.com/GoMini.html/mv_session_id=P5waNnWY

 

[shake this]

You could use any two gears where one has twice as many teeth as the other. For instance, 10 and 20, or 9 and 18.

If you buy from MFG Supply, they have a 9 tooth and a 17 tooth available for #40 chain (in case that's what you're using). That would cut the speed almost in half. Their website is http://www.mfgsupply.com/GoMini.html/mv_session_id=P5waNnWY

That's perfect because I have a #40 chain. and I don't know why I didn't think about the simple math to figure out the sprocket size.

 

[robbie]

Yeah, once you get your brain pointed in the right direction it all starts to make sense. These are the same sprockets I've used on my kart and bike. I like the smaller sprockets because they don't get in the way.

If you want to figure out your speed, gear ratios, engine RPM, etc, check out these equations. http://www.diygokarts.com/vb/showthread.php?t=9591 Take note of whether your governor is still in place, or if it has been removed or bypassed. Your engine will spin a lot faster than 3600 RPM when you remove the governor linkage, especially if you use a higher ratio to slow the kart down. It sounds funny, but if you gear for high speed your engine can bog down and you'll go slow, but if you gear for lower speed the engine is able to wind up to 4 or 5k RPM, and you end up going really fast. That's what my 2.5 hp kart and bike do.

So, if you're gearing down to go slow, make sure your throttle is connected through the governor, or put a stop on it. The governor will be better than a throttle stop because it will allow full throttle on the engine for good acceleration (won't burn up the clutch) but won't let the kart go over your governed speed.

 

[shake this]

The first thing I did when putting the engine back together was to make sure the governor was hooked up and functioning.

The first thing I did when putting the engine back together was to make sure the governor was hooked up and functioning. The last thing I need is for parts to start flying out with her driving.

 

[robbie]

No problem, then. Just plug your numbers into the equations and assume 3600 RPM.

 

[shake this]

great...thanks again for all the help.

 

[shake this]

Sorry to bring this thread back up but after further research, I have more questions. Better yet, asking for opinions.

Gave my daughter the kart this weekend and she absolutely loves it. Pulled the throttle down until I could gather the parts to build a jackshaft. Boy it doesnt take it long for the clutch to get hot. I'm shure the fact that my daughter hasn't gotten confertable yet and drives by pushing the throttle down then releasing and down...I'm sure you all get the point has alot to do with the hell she is putting the clutch through.

So after my research, it looks like it's going to run me about $80 to set up a jackshaft. What would be the smartest option, build a jackshaft or pick up a 2.5hp clone with coupon for $112.

Ive also found springs that will let your clutch engage sooner. One set is for 800 RPM's (figured to low) but the next step is 1200 (figured this might work) but is for Hillard clutch. Even if I buy the new clutch so I could use the springs, this would be the cheapest option but is it the best?