Building Outside the Box

[LVScottT]

I'm designing a two-seat offroad kart and have incorporated a few unorthodox features. I'm curious how many others have designed "outside the box"?

One of my ideas is for a two-person bench seat. I need it wide enough for one adult and one child, so about 36". I also want it to weather well and look good. My solution: https://a.co/d/adB5g3W

Another feature is a 2nd jackshaft mounted aft of the engine, above the frame, with a 10" brake rotor (disc) and a 60-tooth sprocket (also about 10"). This shaft is connected to the live axle via TWO pairs of 16-tooth sprockets and some 420 chain. This configuration removes the two 10" components from the rear axle which greatly increases ground clearance.

OK, let the rants begin!

 

[Denny]

Well that set up sounds interesting. Let me ask you a question what do you do for brakes when a chain breaks or falls off randomly? If you build it to fit 2 adults when your kid out grows you by a foot he can drive you around. They do grow fast these days.

 

[LVScottT]

First, there are two 420 chains from the jack to the axle, so they would both have to break. Plus, there will be a 4.5" band brake (or internal drum, haven't decided) on the live axle with a standard hand brake lever for both parking and emergency secondary brake. And if both of the 420s break and I survive, I'll upgrade them to 50s.

My youngest is almost 40. The passengers will most likely be the grandkids. And yes, they do!

 

[bob58o]

Where is the first jackshaft?

 

[ezcome-ezgo]

Is this what you are describing?

 

[LVScottT]

I believe the driven shaft of the torque converter is referred to as a jackshaft, so I am adding a 2nd jackshaft.

And yes, EZ, except you left out the TC. And my engine is 6-sided, not 5.

 

[bob58o]

You never mentioned the TC, so how can we talk about the second thing if we won’t bring up the first thing?

 

[LVScottT]

My bad. Let me fill in a few gaps.

I am using MS Visio to design it and Excel to track parts & costs, calc ratios & speeds, etc. I have a stock HF 420 still in the box. I will be attaching GoPowerSports' 40 series TC with a 10-tooth driven. A 420 chain goes to a 60t on a raised jackshaft then two 420 chains to the 1" live axle.

Most parts are from BMI Karts. Most of the hardware is from McMaster Carr. The raw steel is from a local distributor. The rest is from Amazon, Walmart, etc.

For the torque converter, I chose G.P.S. over BMI Carts or BlastLED because their backing plate looks the beefiest and I like their cover. My 2nd choice would be BlastLED.

Primary braking is BMI's MCP Dual Line hydraulic master cylinder to their MCP calipers and a 10" rotor on the jack. And I've already explained the secondary hand brake.

14" EMPI clone rack & pinion steering gear box from Amazon, independent double A-arms in front and a 30" trailing arm in back. 11" hydraulic shocks all around. 3/4" spindles. SunF 18/9.5-8 on 8" rims in back, SunF 145/70-6 on 6" rims up front.

Total cost should come in around $3800.

 

[bob58o]

4.5” band brake will not be sufficient.
I might consider putting another rotor outside the axle hanger bearing next to the rear tire and using hydraulics there as well.

id rather have the brake on the axle instead of the jackshaft.

 

[ezcome-ezgo]

two 420 chains to the 1" live axle

The ratio here is 1:1?

 

[Denny]

The ratio here is 1:1?

No, the ratio is 6:1. Only 1:1 from jack shaft to axle which will work.

 

[ezcome-ezgo]

No, the ratio is 6:1. Only 1:1 from jack shaft to axle which will work.

That was my question; what is the ratio from jackshaft to axle? It should be 1:1 or close to it.

 

[bob58o]

Seems reasonable to me.
420cc w/40 series
14.6 : 1 in low gear
6 : 1 in high gear
18” tires

32mph at 3600 RPM
37mph at 4200 RPM

I’m not sure the exact engagement speed of knock off 40 series primary clutches, but assuming 1800 RPM…

Primary clutch should be fully engaged by 7 mph. This seems fine unless you plan to cruise around at less than 7mph. (At 7 mph you that 4.5” band brake might slow you down, lol)

 

[bob58o]

Will there be chain kink issues with the brake on the jackshaft? If the axle sprocket is trying to push the chain up towards the brake rotor, in my head I see the chain kinking. Just what popped into my head.

 

[Denny]

That 41/2” brake band will stop that kart better than you think. Had that on my Manco with 22” tires and it would drag them on asphalt!

 

[LVScottT]

Won't know till I build it.

Should I skip the 420 setup and go straight to 50?

 

[LVScottT]

420cc w/40 series
14.6 : 1 in low gear
6 : 1 in high gear
18” tires

32mph at 3600 RPM
37mph at 4200 RPM

Yep. That's about what I figured. I was also toying with the idea of throwing in a 40 series FNR for $300 from BlastLED but I'm not sure I'll have room.

 

[bob58o]

That 41/2” brake band will stop that kart better than you think. Had that on my Manco with 22” tires and it would drag them on asphalt!

I had my band brake work like that once. Enough to get a video, then it never worked the same. Honestly my cable was too short. When another heavy weight joined me as a passenger…. The suspension and brake cable length were tested. Suspension was fine. Cable snapped.

I think I had some bald 16” snow hog tires. I’m not sure the stopping distance. 3/4 of a house?

 

[bob58o]

Won't know till I build it.

Should I skip the 420 setup and go straight to 50?

No I don’t think so. I don’t know Jack about Jill’s chains. Carry on. I just like typing, otherwise all my delusions just stay inside my head. Not sharing the fun would be selfish.

 

[Denny]

The 40 should be strong enough considering you’re doubling it up.