Very fast lawnmower question

So I am building a tractor with a motorcycle engine and a go kart style rearend. like the one in this video below. I was wondering for the rear axle I got a 32x1 inch go kart axle. Should I use a pillow block bearing that will attach to the stock tranny mounts on a lawnmower. Or should I drill a hole through the frame and mount 2 bearings on the frame of the tractor? I am sure I will be asking more questions as times go on.
https://www.youtube.com/watch?v=yAW1wg_WJwA

Oh the tractor is a craftsman old grey one..

I suggest pillow blocks, mainly for the high RPMs , strength and servicability ( can grease em) - they work for building ventilation systems so should work great on a tractor - all my mods are using pillow block berings.

I picked up a 32x1 inch axle for it with 2 of these bearings (http://www.ebay.com/itm/2-DODGE-F4BSC204-2-1-4-4-BOLT-FLANGE-BALL-BEARINGS-/271098320214?pt=LH_DefaultDomain_0&hash=item3f1eb81556)

What I also wanted to know is what do I do to keep the sprocket from moving from side to side when I put it on the axle shaft?? I imagine it goes on with a keyway but do I use a spacer to hold it center? Thanks

You can use lock collars to keep the sprocket from floating on the axle.
You should be able to find them at TSC, NAPA...etc.
Or online
http://www.mfgsupply.com/gomini/gominisprockets/gominisprocketscollar.html

What size sprocket should I use?

How do I make sure the lock collars do not move around? The threads might not hold up on the bolt to tighten them....

Lock collars do a great job of staying where they are supposed to... we use the crap out of them.

CraftsMAN wrote:

How do I make sure the lock collars do not move around? The threads might not hold up on the bolt to tighten them....

Couple of ways to lock set screws down so they don't move

Before you install the setscrew take a drill and bit smaller than the ID of the threads, and drill a dimple in the shaft. It doesn't take much of a dimple.

Then use some thread locker on the set screw to keep it from backing out. Red if its permanent, Blue if you want to take it apart later. Or if you are really cheap and don't care if it comes out, Superglue makes a good thread lock, It may or may not come apart afterward though

Or you can skip the dimple and just use the threadlocker, pretty weak though

I personally would drill and tap for a second set screwm opposite the first, dimple both, and Loctite them in

OK so I got the craftsman all ripped apart. Steering question...
Do I use this? http://www.ebay.com/itm/Go-Kart-ATV-Go-Cart-Steering-Kit-Complete-Package-/160663516141?pt=Go_Karts&hash=item25684ab3ed
Or this ? http://www.ebay.com/itm/Front-Steering-Axle-Assembly-25-Go-Kart-Dune-Buggy-250cc-TAOTAO-ROKETA-SUNL-BMS-/150918113128?pt=Go_Karts&hash=item23236ba768&vxp=mtr

Looks like direct steer versus rack & pinion...
They would both work, it just depends on your preference. Some people would say not to use direct steer on an off-road machine... some would say go for it.
I built a direct-steer setup on my mower, mainly because I prefer a hand throttle over a foot throttle. Honestly you will get a whole lot more feedback from a direct steer... as you hit & run over things the steering wheel will want to jerk left or right. The rack & pinion steering will feel closer to a stock mower setup; it will take multiple turns of the wheel to go full-lock to the left or right. Like a kart vs. a mower... it will steer slower, but with less feedback thru the steering wheel.

I would be using a foot throttle..

I need room under the hood so steering cant get in the way. I would like to keep the steering under the frame if possible. Here is my most recent video.. https://www.youtube.com/watch?v=R3TAI3c9xzM

So what size sprocket should I use? I want a good balance of top end and low end.

I Need to know a few things

First off which engine are you using?
Make and model of the bike its coming from is all I need to know

Output sprocket size on the engine, are you using the shifter, or will it be in locked in gear?

Tire size

expected top speed

I should be able to find the gear ratios for the engine on line, if not, the engine sprocket size is all i need

The rear tires are 18x8.5x8 and the engine will be a 400cc yamaha engine most likely. I will be using the shifter. Expected top speed not really worried. About 50 lets say ?

CraftsMAN wrote:

The rear tires are 18x8.5x8 and the engine will be a 400cc yamaha engine most likely. I will be using the shifter. Expected top speed not really worried. About 50 lets say ?

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Is it a dirt bike ir street bike engine, 2 stroke or 4 stroke

Do you know the model of the bike its coming from?

I just ran the numbers using the stock Yamaha XS 400 twin with a stock 16 tooth sprocket, assuming a 4th gear ratio of 1 to 1 ( 5th and sixth gear are usually overdrives) Its the only old yamaha 400 with electric start. Using a kick start engine in a tractor would be a pain.

with a 60 tooth rear sprocket you would expect a top speed of 100 mph @ 7000 rpm
a 70 tooth sprocket would get you down to 85 mph, however a 70 tooth sprocket is huge, nearly the size of the tire

if you add a jackshaft with a 20 tooth input sprocket and a 10 tooth output sprocket and use a 50 tooth rear sprocket you can cut you're top speed to 60 mph @ 7000 rpm.

if you add a jackshaft with a 32 tooth input sprocket and a 10 tooth output sprocket and use a 40 tooth rear sprocket you can cut you're top speed to 45 mph @ 7000 rpm.

How much pulling power do you want?

It would be off of a street bike 4 stroke. I would like some good low end..

CraftsMAN wrote:

It would be off of a street bike 4 stroke. I would like some good low end..

All the old yamaha 4 stroke 400s were about the same horsepower. I wouldn't bother trying to use a kickstart motor, unless you can figure out some fancy rigging to actuate the kicker. A 400 single is damn hard to kick over even for me, and I weight 240 lbs. Doing it on a tractor would be extremely difficult.

"if you add a jackshaft with a 32 tooth input sprocket and a 10 tooth output sprocket and use a 40 tooth rear sprocket you can cut you're top speed to 45 mph @ 7000 rpm."

This forumula should work quite well, You pretty much have to run a jackshaft or you won't get nearly the ratio you need to get the speed down to 50 or so. The formula is based on the Yamaha 400 twin with a 16 tooth engine sprocket.

A 70 tooth sprocket is 14-1/2" around and it will get you down to 85 mph with out a jackshaft, but you won't have much bottom end.

This might sound stupid but I have no idea what a jackshaft is..

Like a dual chain set up?

a jackshaft is a shaft between the engine and your axle. It can be used to correct alignment issue, or for extra gear reduction.

It is basically a shaft with 2 sprockets on pillow block bearings, sprocket sizes determin the ratios.

http://en.wikipedia.org/wiki/Jackshaft

Oh I see now. I am unsure if I have the room to run one of those? I am going to pick up the engine tomorrow. It should have all of the wiring but if it does not ebay will be making some $ off of me. lol. As for kick start check out the first link. The second link is of the tractor so far.
https://www.youtube.com/watch?v=ePt0WgWZZ0Y
https://www.youtube.com/watch?v=TBtjV2SRyUs

I need to know the model of the bike for any better info.
an 80 tooth #50 sprocket is 16.5 inches in diameter. you'ld only have an inch or so clearance under the sprocket.


A jackshaft only takes as much space as the largest sprocket plus a little for chain and guard clearance.

Mine only uses a roughly 5"x 5" area 12" wide, and it could be narrower, I could have used a shorter shaft.