New Kart Project - Seeking Engine Advice

[doesgo]

I just obtained a kart that's nearly a complete roller for $50. However, some parts are still needed, including an engine and clutch (and seat, chain, brakes, brake linkage...). I'm looking for some ballpark recommendations so I can narrow my research before I start working on it. I promised the wife I'd finish up three other project at home before working on the kart, so I probably won't start on it for six to eight weeks.

It appears to be a decent foundation (but with a few less-than-ideal parts and characteristics) for a family fun. I'll be buying a new engine for this kart, but of course cost is a factor.

Anyway, the specs:
- welded frame with cage made of 1" square steel tubing (not sure of wall thickness)
- will be for off-road use on grass, relatively flat farm fields, gravel roads, and undulating four-wheeler trails
- front suspension with coil-over shocks and 6" travel (front ground clearance is 3" min, 9" max)
- no rear suspension (6" ground clearance)
- 17.5" diameter rear tires, circumference is 55" (looks like they're off a golf cart, Goodyear Terra-Tire)
- 1" diameter live axle
- 54-tooth sprocket welded to axle
- 260 pounds as is, plus engine, clutch, seat, brakes
- wheelbase is 66"
- frame is 83" long by 24" wide
- track width front and rear is 45"
- drivers will typically range from 150lb to 250lb

Performance Goal: Fun acceleration, ability to spin tires on dirt and grass from a dead stop, top out around 40 mph if possible (will be limited for less-experienced drivers). Acceleration goal is more important than speed goal.

Questions:
1) Approximately how much power will be required to achieve my goals, assuming proper gearing? Engines sure get spendy as you get past 10hp!

2) Do you typically get what you pay for with engines? Prices vary a lot between no-name brands, Tecumseh, B&S, and Honda, with a Honda costing nearly twice what an off-brand engine does with the same power rating.

3) Assuming my 54-tooth driven sprocket will be acceptable, approximately what tooth engine sprocket should I start with?

4) How do I know what type of chain to use with this sprocket?

5) What is the maximum usable rpm these 8-13hp engines typically achieve?

6) The front wheels and tires appear to be off a riding mower. Will those and the golf kart rear tires survive 35-40 mph or am I asking for trouble?

7) What's a jack shaft and what's it used for?

8) Any other quick tips or recommendations for me?

Thanks a lot!

 

[NJOHC]

A 10 tooth engine sprocket will get you the speed you want and probably some more. I was clocked in at 45 on a stock 5 hp dingo with 9t engine and 54t axle. As far as the engine, the link I provided below is the best I found while looking for engines. Its a honda clone. Its decent quality, but for the power Id go for it. We bought a 9hp and places like the gas tank its obvious its a chinese honda wannabe. They're supposed to perform just as well so I dont see much of a downside. You just need to check over things and maybe re-enforce the gas tank. That has been a problem on my friend's kart. A jackshaft is the shaft that sticks out of the engine where w/e type of torque converter you want to use will go. I dont think the tires will be much of a problem. The engine I gave you a link for makes all it hp at 3600 rpm which it where its limited to rev to.

http://www.surpluscenter.com/item.asp?UID=2009051115495322&item=28-1677-E&catname=engines

Good luck!

 

[modelengineer]

I advise buying a whole motorbike which has been crashed, taking out the engine and brakes, and selling the rest as spare parts. My 2007 gs-500 engine will be free for me once I sell the rest of the parts which I have.

 

[theo]

I would also think about putting some sort of suspension in the rear.

theo

 

[doesgo]

Thanks NJOHC! What diameter tires did you have with your 9/54 combo? I just calculated the speed at 3600rpm with 18" diameter tires and a 9/54 combo and it only gave me 32.1 mph. 10t engine would potentially give me 35.7 mph, 11t would be potentially 39.3 mph.

It's hard to argue with the price of that engine if it's any good! $235 shipped; far cheaper than anything else I've found.




modelengineer,
GS500 engine in a kart? Wow man, you should have no lack of power! How are you mounting the fuel tank? Do you have a thread on this forum with your build-up? I'd love to check it out.

I'm definitely interested in looking into that type of project at some point, but as of right now I just want to use a simple, self-contained, bolt-on engine.




Interesting recommendation, theo. I'd like a rear suspension, but if the engine is mounted to the frame, how does one keep the chain tension acceptable? Alternatively, if the engine is mounted on the axle, that would require a different axle design than I currently have and the unsprung weight would be so high that it seems much of the advantage of a rear suspension wouldn't be realized.

I'm interested, but at this point I just want to get this rig put together and running well more or less as is. After that, I'll see what things I don't like about it and address them as I go, possibly including a rear suspension.

 

[theo]

You can go with the simplest and that is hinge the back part of the frame and mount the engine and clutch on it. Not the best but it does soften the blows.

theo

 

[doesgo]

Hmmm, that would simplify the design. What do people typically use for springs and shocks? I'll have to poke around and find some examples.

 

[theo]

I would look on ebay for a pair or quad front shocks, or sled front shocks.

theo

 

[NJOHC]

I had 18in tires if I remember right. They were 18/9.5x8 carslisle knobby tires. That was when I first got my kart with the used motor. I guess that goes to show you the variables with the gear ratio calcs. I was clocked in by a truck riding beside me. It was also a very bumpy road so I couldnt stay in it for too long. I had a torque converter too, which I dont know if the caclulator accounts for the overdrive etc it goes in to. I think its just based off a centrifugal clutch for racing karts. If you put some suspension on it be sure to post it up! Im thinking about it for mine when I get some more power out of my little Subaru motor.

 

[motor_head]

shaft coming out of the engine is the crankshaft a jackshaft is a shaft that is totaly seperate and is only connected by chains and belts

 

[choppedandtwisted]

Be sure to check out craigslist too for engines. There are usually 3 - 4 good candidates every time I look.

 

[doesgo]

shaft coming out of the engine is the crankshaft a jackshaft is a shaft that is totaly seperate and is only connected by chains and belts

What's the jackshaft's purpose? I've only seen it referenced in discussions of torque converters.

Would you think the mounts shown in the picture below were for a jackshaft?

 

[Jerryburger]

Yes- thats where the jackshaft used to be. Those are bearing hangers.
I'm guessing your rear sprocket is a #40 or #41 type. The most common clutch for that size chain has a 10t sprocket on it, giving you right at 36mph @ 3600 rpm. A 6.5hp clone would move it up top speed fine- it probably wouldn't have crazy acceleration, but it should heep you happy. If you go with a larger motor, the top-speed would be the same (same gearing) but quicker acceleration. The down-side to the bigger motor is the cost of the clutch- it jumps up to about $60, instead of $30. That 11 HP WORLDAIRE engine would spin the tires for sure. If you have the $,,,, You could use the jackshaft mounts to bolt up a #40 comet torque converter. I'd run a 15t output on the final drive, which would up your top speed into the low 40's, but give you even better take-off than the clutch set up. As you might have guessed #40 Comet torque converters AREN'T cheap.
By the way COOL KART! And I wouldn't add suspension to it. Half the fun of these things is their simplicity and crazy handling!

 

[doesgo]

Great post! Thanks so much for taking the time.

Makes sense. Is there a reason to have a jackshaft if you don't have a torque converter?

If a 6.5hp would likely get me the speed I want but not the acceleration, I could bump up to Worldaire 11hp or HF 11hp or 13hp and gear a little taller to gain some mph as well as low-end grunt. Are engine sprockets with varying tooth counts typically available? If I'm buying a new engine, I'm thinking I should get more than I think I'll need just in case.

A $30 premium for the clutch is no big deal, but $240 for a torque converter (over $300 total, I assume, when you include the jackshaft, bearings, belt, etc.) is a bit much. I'll get a decent engine and set up the basics, but until I determine whether this rig will get a lot of use I don't want to pour too much money into it.

Thanks for the kind words about the kart! I think it's pretty darn cool as well, but I'm new to the scene after about a 26-year absence and I see a lot of other cool stuff out there. My dad and I made my first kart of wood, it had foot-steering, solid tires (non-pneumatic), no bearings, no brakes, and a 3.5hp B&S. We sure tore up that left-rear "tire"! My dad screwed about six metal brackets to the tire so we could get some traction on grass and dirt. Clocked it at 35mph (my dad paced me in his car). I still have that kart, and now that I've got the bug again, I'm thinking I might resurrect it, maybe with an HF 6.5hp. Pneumatic tires this time, though.

 

[modelengineer]

It allows you to get much higher/lower ratio's. Also, it means you can have a smaller sprocket on the rear axle - meaning more ground clearance. Usually the sprocket is the lowest thing on a live-axle kart (besides the wheels, lol!).

e.g you could have all your reduction done on the engine-jackshaft chain, then on the jackshaft-axle you could have two small (15 tooth or so) sprockets to maximise ground clearance.

 

[Kenny_McCormic]

You will not spin tires with a cent clutch.

 

[doesgo]

It allows you to get much higher/lower ratio's. Also, it means you can have a smaller sprocket on the rear axle - meaning more ground clearance. Usually the sprocket is the lowest thing on a live-axle kart (besides the wheels, lol!).

e.g you could have all your reduction done on the engine-jackshaft chain, then on the jackshaft-axle you could have two small (15 tooth or so) sprockets to maximise ground clearance.

Ahh, so you play with different sprockets on the jackshaft, giving different ratios to the live axle. Got it. I was thinking the jackshaft had the same driven and drive sprockets. Makes sense! Thanks.

By the way, there's a 40 and a 54 stamped on the axle sprocket. It's got 54 teeth, so can I safely assume the 40 means it takes a #40 chain?

 

[Kaptain Krunch]

you know what assuming does right? either way yes 40 should be the chain pitch haha.

 

[doesgo]

Yes, I knew it was risky to ***-u-me anything, but I had to take that chance. Thanks for the chain type confirmation.

 

[doesgo]

...