Need help with gearing Please

[robertnoble]

Hi new here. My kart started out as a Manco Silver Fox, but has had everything pretty much changed from custom tubular a-arms mounted to the Yerf Dog Central Locating box, 1 inch d.o.m. tubing mandral bent to widen the kart for rci buckets and five point belts, hydraulic disc brakes, and so on and on. My question is I really wanted to go with the comet forward reverse gear box which is rated for 16 h.p. but the motor I am using is the 16 horse duromax and I think it would be border line of tearing it up. So here is where I need the help. Kart Specs... 22 inch rear tires, comet 40 series clutch with 10t sprocket, Kart is about 580lbs with no riders. What jackshaft gear and live axle gear do I need to get 40 to 45 mph and still have some torque without hurting the converter. The motor is rated at 3600 r.p.m. Any help would be a great appreciation. Thanks Robert

[metalstudman1]

Welcome-That's a pretty heavy Silverfox!!! At least you have an engine that'll make some torque. How about some pic's.
What size driven unit do you have now? I'd guess with a standard 7-1/2" driven and your 22" tires you'd need around a 40t-46t axle sprocket to reach 40-45mph. There are plenty of ratio calculators on-line available for you to input in your components and see which way to go.

[robertnoble]

Thanks for the reply. Ill get some pics up soon. The kart is in my pole barn and I work second shift for g.m. So I only get to go and play on the weekends. With a two year old in the morning not much time. The weight was based off the 13.5 hp stock manco silverfox that has a curb weight of 472lbs. Since I added some tubing to widen the kart, and put the yerf dog front end on with 16 1/2 fox shocks all the way around, bigger tires, although I went with Douglas Aluminum Rims, I just put the Kart at 500 .lbs to be safe. That was another question Would I have been better off going with the Bigger diiameter Driven? I can always send my 7 1/2 back and get the 8 1/2. I am a great fab/Mech. but don't understand the gearing part and converter part that well. I really appreciate your help and time. Thanks again... Robert

[metalstudman1]

I use sprocket/gear calculator charts first to get an idea,then experimantation usually takes over!!! I've found 2.8 - 3.5 ratio works for our off roading. Most people think 45mph is slow- out on the trails that's FLYING!The comet gearbox will work (the ones I've seen have taken some pretty harsh abuse)Reverse is pretty important!! Do you have room for the gearbox?
* (by the way you listed the weight @ 580Lbs. originally- that's why I said it was heavy)

[robertnoble]

My wife really wanted the comet gear box but I wasn't sure. It says it is rated for 16hp which is exactly what I have just didn't no if it would be border line. I have plenty of room for it. The rear swing arm was all re done and lengthened and have ample room for it. Do you think it would hold up ok with the 16hp motor and if so, what sprocket on the end of the gear box and live axle sprocket would I then need. I see BMI Karts sells the gear box and man would my wife be happy because she was concerned about pushing it out of the pole barn when I am at work so the son and her could use it.... Thanks again your a real big help... Robert

[metalstudman1]

Never owned/used the gearbox but have had contact with a kart that had one- it had a 2-stroke snowmobile engine hooked to it with a 700 series driven (I'd guess 16hp+) -I worked on everything else on that kart but the gearbox! IMO-Comet had been around too long and provided too many universal items to over-rate a product it might have to warranty. But since they closed their doors parts may be hard to come by, I'd check parts availabilty before buying one.
I'm using a Polaris tranny (50hp rated)-but I converted it to a chain drive instead of a driven unit.
Another member mentioned he's using a Polaris tranny on his Manco- "SFORCES" you might want to PM him to see what he did as an alternative.

[robertnoble]

I see polaris trannies are fairly cheap. Would you be willing to tell me what I need to buy and how to hook it up to my 16hp kart. I have no problem converting to chain drive either. I am very good listener and comprehend things easily I am a street rod guy and this is out of my league but really want to learn and be good at this. Thanks again. If your willing I would really appreciate it.. Thanks Robert

[metalstudman1]

The Polaris Driven is about an 8"-9" and uses a 1-1/8" wide belt, so trying to use your Comet 40 clutch may not work as it only uses a 3/4" belt. Did you try to PM "SFORCES"?: http://www.buggymasters.com/forum/member.php?u=1196area
He has a 16hp and a Polaris tranny but have never seen a pic of the engine area to see what he did to get power to the tranny.
If you care to do some reading you can look at some of the pic's on my "Frankenbuggy" thread for ideas: http://www.buggymasters.com/forum/showthread.php?t=1290
I'll do some thinking (that might be scary!)to see if I can figure out something!The obstacles are the input side of the Polaris tranny is splined, it is about 3/4" dia. and could be removed from the unit and turned down smooth and a keyway added for a 40 series driven ,but that cost may not make it cost effective. The Polaris clutch has a tapered application- I'll look and see if you could possibly replace the tapered shaft for a straight one or modify it.

[robertnoble]

Hi, Yes I P.Med him right after your post last night and he never got back with me. Your help is greatly appreciated...

[metalstudman1]

Bigkid's tranny is the same one I have- mine is out of a Trailboss, but I'm sure it was used in multiple quads.

[metalstudman1]

I have another dead Polaris being donated to me (should get it Fri.-Sat.) I'll take some pic's for you to see the original equipment and see if a 3/4" belt will work on the driven.

[robertnoble]

Hi thanks so much for your help. I bought a f,n,r, out of a polaris trail boss. My friend who owns a machine shop is turning down the shaft. The smooth part of the shaft was .780 so he is turning the splined shaft and the smooth shaft down to .750 for the comet 7 1/2 driven and putting a 1/4 inch key way in it. My new question to you is what gear do I use on the output so that it will match up to my 40 41 chain sprocket on my live axle. I want to run a 10t on the output and like a 45t on the live to get about 40 mph. Im just not sure does polaris make a sprocket for this chain size or what do I need to do. Thanks so much and will be waiting to here back from you. Take care... Robert

[metalstudman1]

Good deal!!!Your output sprocket is #520 and 11t. No they don't make a #40/41 sprocket for the Polaris tranny that I've found with the correct spline count, I found lots of ones very close but they wouldn't fit- I did finally find a 12t (#520 again) sprocket for mine to increase topend.(output sprocket increase of 1 tooth is about the same as going down on the axle sprocket by 3-4 teeth)
I have no experience with this tranny using the driven-and that final gear ratio.
Is your axle "HEX" style? if so then your sprocket carrier should just slide over the axle and easily modified for a #520 sprocket by just redrilling some holes.Can you post a pic of your axle/carrier? and I'll provide an opinion/option based off what I see.

[GX150]

See this thread about using a custom sprocket:

http://buggynews.com/my-340-sand-viper-project-t31189.html

[robertnoble]

First of all you guys have been so awesome on helping out a newbee. I talked to Sforces tonight which has the same motor etc as mine. I am now having the output shaft also turned down with a 3/16 key hole to accept the 40 chain sprocket. He was also kind enough to tell me what sprockets to buy for my 45-50mph range. What a great site you guys have. Your making this buggy building fun. Thanks again and ill post pics soon as I get little farther in fab work. P.S. I am so glad I seen your post of re enforcing the a arm mounting points on my yerf setup I am putting on. Thanks. Your the Man....