Reverse Gear for 670 Predator

[ActualFactuals]

I'm brand-new to building carts, so if I have bad questions please bear with me.
I'm trying to build a one-seater off road/go cart hybrid with a 670 V-Twin Predator engine from Harbor Freight. I'm probably going to mount the engine on a swing arm right above the rear axle to make the rear suspension easier.
My questions are:
- How should the drive train actually be configured? I know that most people mount a torque converter to the output shaft on the engine but how where does the train move from there? I've seen a few videos about what I'm trying to do and it seems that it's straight to the live axle from there.
- Following that, how could I get a reverse gear (I'm pretty sure torque converters are not transmissions).
- What torque converter, if the recommended drive train requires one, should I use? The beefiest torque converter I have seen is a 40-series which is only rated up to 18hp (the engine I want to use is 22 hp).
- What transmission should I use to get a forward and reverse gear? Preferably the more speeds the better, but I'm only worried about forward and reverse. Secondly, what transmission would be able to handle the output of the engine?
Thank you very much for any recommendations that are made.

 

[landuse]

Research the comet FNR gearbox. That might be an idea for you

 

[HoldenIron]

A 40 series torque converter eats belts in a 670...like in 20 minutes of joy riding it will eat belts...especially if there are two people in the kart and pulling any inclines. You need a Comet 780 torque center or even stronger a Comet 1190 series.

 

[Kartorbust]

You may have to look for a transmission from say a John Deere Gator. I'm watching how Rather B Welding is doing up his 3 speed with reverse homemade gearbox. The old Comet FNR gearbox is only rated for 16hp tops.

https://www.youtube.com/watch?v=_qlVgWnYs7g&t=4s

 

[67StingrayJ]

there seriously needs to be a better solution to this problem. Comet FNRs don't exist any more. RPM gearboxes are way to expensive, plus overkill. The ebay model FNRs can't withstand the HP, 13 max. And the polaris FNRs are so vast its almost impossible to know exactly what to buy.

Someone needs to come up with a solution. something in the $200 - $250 price range and can hold up to +/- 25hp.

If anyone has had success in putting a FNR on their 13hp+ buggy speak up, and be specific. Tell us how it worked, give us part numbers, manufacturers, make sure it's still available, roughly what you paid, what hp it's rated for.

 

[Kartorbust]

I do agree with that. I mean I'd be down to pay $500+ for one that can hold up to 75+hp. I'm a daily frequentor of minibuggy.net and there really has not been anybody that has come up with a cheap solution to a reverse gear. Outside of using existing gearboxes from ATVs that are divorced from the engine, a starter with a ring gear mounted to the spool or in it's own chain gear reduction setup.

The only other option would be maybe contacting members of a Baja SAE team and ask if you can purchase their old gearboxes from previous years that they might have, or ask if they can make you one. Granted they usually only build them for a Briggs Model 19 10hp gross engine, but do we have many options anymore? A lot of teams look for ways they could make money to help fund their program at their college/university. Well they could engineer, build and sell gearboxes to those who want one. I'd support the local UNL Baja team if they'd do this.

 

[67StingrayJ]

Seriously, there should be a listing, or possible a new thread with all the different gearboxes that we have to choose from. The list should include:

1. Part number
2. Year make and model of platform it originated.
3. HP rating -or- engine cc of model it originated.
4. Forward/High gear reduction ratio
5. Low gear reduction ratio (if applicable)
6. Drive axle/shaft diameter
7. Drive axle keyed or splined
8. Driven axle/shaft diameter
9. Driven axle/shaft keyed or splined
10. CVT or chain driven
11. Sprocket size (if applicable)

Anything else?

 

[Kartorbust]

There isn't much out there. Polaris Trailboss 250 high low gearbox, the Dana-Spicer H12 transaxle, that's about it off the top of my head. Like I've said before, you could try contacting a local college/university SAE Baja team and see if they will sell either a completed gearbox or build one for you, long as you give them the metal to do it. Or contact a machine tool/die class at a trade/tech school.

Go karts, mini buggy/UTV are a niche market. Outside of Chinese stuff and limited offerings elsewhere, there isn't much for us. I mean Jeffco is the only other gearbox, but that's $4500...more than what most of us have to spend on a kart or buggy budget wise.

 

[67StingrayJ]

I found a Trailboss 250 gearbox but I'm not sure how I would mate it to my 40 series CVT. Any ideas? The guy selling it said it has a 19 tooth spline and is about .825" diameter. Any help on mating my 40 series to this thing would be much appreciated.

 

[Kartorbust]

Run a chain from the 40 series sprocket to a sprocket on the input side of the trailboss gearbox. That's probably the best way to do it. Then you can mess around with input gear ratios to see what works better for what you want to do. Let us know how well it goes, I'm very curious.

 

[67StingrayJ]

Run a chain from the 40 series sprocket to a sprocket on the input side of the trailboss gearbox. That's probably the best way to do it. Then you can mess around with input gear ratios to see what works better for what you want to do. Let us know how well it goes, I'm very curious.

I wish it were as easy as just running a chain from the CVT to the gearbox but how? the thing has splines that I can't find anything to fit, letalone any real specifications to mention of what the trailboss gearbox actually has.

It's beyond my patience right now and I don't have the money to buy an expensive gearbox that I may or may not be able to use without some major modifications. I guess what I'm saying is someone else can give it a try.

 

[JTSpeedDemon]

What is there in the way of OEM sprockets for the Trailboss gearbox? Might try that.

 

[Kartorbust]

I would read through this guy's build. He used a Trailboss gearbox, did a chain drive from the engine to the gearbox. You could always contact a machine shop to see if they could help you out, maybe get splines cut on to a sprocket for you or something to make it work.

Of course I'd for get the frickin link. http://www.minibuggy.net/forum/projects-progress/18351-davids-250-micro-burst.html

 

[Joe-405]

I’ve always wanted to use a hydra static one off a riding mower. Because of the variable throttle stuff. But there is this one but it’s $1050 but rated to 500hp.

https://thekneeslider.com/reverse-gearbox-for-motorcycle-powered-cars-from-roadstercycle/

 

[Kartorbust]

It sucks that we are in a very small niche market and seems to get smaller everyday. Nobody builds things anymore, they would rather buy a $10,000+ machine that does all that, then wreck it soon as it's off the trailer. If there were more people willing to build buggies and the like and need reverse, there would be more options besides the discontinued Dana H12, that $1050 500hp gearbox, the $4500 Jeffco box, and the cheap Chinese gearboxes that will grenade as soon as you put more than 8hp behind it.

Once college starts back up within the next couple weeks, I may try calling the University of Nebraska at Lincoln and get in contact with the Baja SAE team and see if they will make gearboxes to sell to help fund their team. I mean they are engineering students, and we do not have many other options to go off of. It seems like those teams end up in similar situations, where they have a hard time locating a gearbox or they build one. Usually from what I've seen on their forums is, they build them with all the reduction internal to the box and run CV axles to the wheels, rather than messing with chains for the final. Usually they run around 8:1 final and with the CVTs they run on a Briggs and Stratton 10hp Model 19, get upwards of 30-35mph. Which for most, seems to be adequate.

But I'm just spitballing anyway at what we could do.

 

[67StingrayJ]

It sucks that we are in a very small niche market and seems to get smaller everyday. Nobody builds things anymore, they would rather buy a $10,000+ machine that does all that, then wreck it soon as it's off the trailer. If there were more people willing to build buggies and the like and need reverse, there would be more options besides the discontinued Dana H12, that $1050 500hp gearbox, the $4500 Jeffco box, and the cheap Chinese gearboxes that will grenade as soon as you put more than 8hp behind it.

Once college starts back up within the next couple weeks, I may try calling the University of Nebraska at Lincoln and get in contact with the Baja SAE team and see if they will make gearboxes to sell to help fund their team. I mean they are engineering students, and we do not have many other options to go off of. It seems like those teams end up in similar situations, where they have a hard time locating a gearbox or they build one. Usually from what I've seen on their forums is, they build them with all the reduction internal to the box and run CV axles to the wheels, rather than messing with chains for the final. Usually they run around 8:1 final and with the CVTs they run on a Briggs and Stratton 10hp Model 19, get upwards of 30-35mph. Which for most, seems to be adequate.

But I'm just spitballing anyway at what we could do.

I hope you do get somewhere with your local college. Keep us posted.

 

[Kartorbust]

So I did contact the UNL Baja team, however they haven't really started on anything yet. They also mentioned, that once they get going on their build for competition that they would not have any time to build boxes for others. I asked about maybe selling plans for the gearboxes. They responded with that they would not want other competitors to get ahold of them.

So for now, we are S.O.L on that front. I'll keep trying to contact former members from other schools. There was a guy over on MBN a year ago that was a former Iowa Baja team member and was going to be selling plans for mini baja type buggies for people. I was going to see if he still had files for gearboxes by chance, even though it's been about 8 years since he was on the team.

 

[anickode]

Reading back on this thread a bit, it seems like the easiest and most logical solution would be to take a trailboss trans apart and take the input shaft to a machine shop to have it turned smooth and keyed.

 

[Kartorbust]

Reading back on this thread a bit, it seems like the easiest and most logical solution would be to take a trailboss trans apart and take the input shaft to a machine shop to have it turned smooth and keyed.

I have to agree with this. There was another Polaris gearbox I happened to cross last night, mostly any of the 1990s Utility quads like the 400 sportsman I guess had one. Long as there is a divorced gearbox from an ATV that's chain driven, it should be at least doable to use in our applications.

 

[gegcorp2012]

Another option could be the bottom end of a motor that has reverse built in. I picked up a Yamaha Warrior 350 a few months ago that had a missing jug, but the bottom end is supposed to be good. it has a reverse gear built in.

I didnt know what I would do with it until I stumbled on a couple of YT videos last week where people repurpose ATV gearboxes by building an input shaft to take place of the crankshaft, and they close off the topend with a plate.

For example:
https://youtu.be/wDJmsifTWh8

Could be a cheap alternative ...

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