Golf cart motorcycle engine conversion

mullins87 said:

I've never been fortunate enough to get to drive one, but I've seen some shifter carts that were absolutely wicked on the track. They look like way too much fun. I bet you had a lot of fun with yours. My sons have a two seater off-road cart that has a sad, sad 6.5 hp Tecumseh on it...........I better get Frankencart finished before I even start thinking about their cart!

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Don't know how old your sons are my youngest is 13. I think maybe a 80cc or maybe a 125 would be fun. With a seatbelt and helmet.

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My boys are 16 and 12. Obviously the oldest is more interested in my Jeep right now, however I think he might get interested if the cart was capable of near highway speeds!!! You're right, just about any dirt bike engine would be perfect.

I got to work on Frankencart this weekend!!! All of the electrical is done with the exception of physical installation of the gauges, they are already wired up, and the installation of a starter switch. The switch will just have to wait until I can reinstall the body. I'm still having issues with the exhaust, I can't seem to make myself give up on that one. I was brainstorming yesterday afternoon and I think I may have a solution, but it will be a last ditch effort on my part. If it doesn't work, then I'll have to back up and start over. Eventhough I still can't crank it just yet, it is nice to turn the key and see the dash light up again.

Hey, got to work on the cart today!!!! I have spent roughly the last month getting ready for a mission trip to Louisiana last week. So, now that's over and I can get back to Frankencart. Today I got the exhaust system installed!! WooHoo!!!! Next weekend the body will go back on so I can fab up a shifter handle and linkage. Sometime before then I'll also pick up a metal hole saw so I can install the gauges. Sorry fellas, no pictures today of the exhaust.

Keep up the good work, it just takes time. :thumbsup:

Frankencart is alive and kicking!!!! I got the shifter and linkage fabbed up today for the final time, and it works great. In said "for the final time" as it took a couple of failed attempts to get it right. The exhaust turned out exactly as I wanted, it is quieter than the bike was when new. I don't think I'll have any overheating problems, but then again I only had it out for about 20 minutes. Then chain drive is noisier than what I was expecting, but that may just be a minor alignment issue with the sprockets.

I have learned something about motorcycle engines and transmissions. I have been riding motorcycles for 35 years, but I didn't know until this past weekend that a motorcycle transmission input shaft rotates at 1/2 to 1/3 the speed of the crankshaft. I have always dealt with automotive transmissions where the input shaft rotates at crankshaft speed. In essence, if the transmission ratio is 1:1 and the engine is turning 3,500 rpms, then the output shaft of the transmission is also turning at 3,500 rpms. The ratio for 6th gear in this motorcycle transmission is 0.89:1, so I assumed the output shaft of the transmission would be turning faster than the crankshaft. Well, we know what happens when we assume things. Frankencart is slow!!! I put a wrench on the end of the crankshaft and made a mark on the transmission output shaft and starting counting revolutions. I was not expecting to find the crankshaft rotates 2.625 times for every one full rotation of the output shaft in 6th gear. Long story short, I have new sprockets on order that I hope will give me an overall gear ratio that I can live with.

Here are some pictures that I snapped today.







Don't look too closely at the welds on the exhaust system....you may find out I'm not very good at welding thin walled tubing!

:thumbsup::thumbsup: Very nice job, we learn as we go don't we? It will be just what you wanted soon & all the hard work will be worth it.

I got the new sprockets installed, and boy what a difference!! I got a new 10 tooth sprocket to go along with the 14 tooth on the transmission, and a 14 tooth to go along with the 23 tooth on the counter shaft. Before taking into account the 12:1 rear axle ratio, this new combination gives me a final drive ratio of approximately 2.25:1, which means the input shaft on the rear axle is spinning at nearly the same speed as the crankshaft. I am very satisfied with the speed of the cart, first gear is a slow walk at roughly 1,500 rpms, while sixth gear gives me a "sane" speed of about 30-35 mph around 6,000 rpms. To date I've been too chicken to see just how fast it will go. Thing is, with this little engine, 6,000 rpm is just getting into the meat of the torque curve, it wants to go!!!

Wow that is impressive. You may want to install a ROPS, a couple seat belts and helmets if you plan on reving it up. Nice job and ingenuity.:thumbsup:

I've already thought of that!! :biggrin: Buggies Unlimited has a complete front disk brake kit that works in conjunction with the factory rear brakes, and they have a high speed gear set for the rear axle that changes the rear end ratio from 12:1 to 8:1!! With those gears, Frankencart would be capable of getting a speeding ticket on any interstate. The front brakes, better wheels and tires, new bushings and tie rod ends for the front end, a full roll cage, a pair of racing seats with 5 point harnesses and a helmet are a necessity if I go that route. I really don't think I'll be going that route.

As a side note: If the rear axle had a locker, I do believe it would carry the front tires on a good hard launch. :laughing: