GY6 Reverse GearBox Horse Power Limit

[fan4chevy]

I am wondering if anyone knows what the horsepower limit is for the outboard reverse gearbox found on most gy6 engines?

Also, what limits this gearbox from being able to be used on higher horsepower engine swaps? Looks pretty darn strong inside.

http://www.buggydepot.com/buggy-tech...e-gearbox.html

[neo71665]

I believe I've seen somewhere they are rated at 11hp max.

[fan4chevy]

Thanks,

I opened one of mine up today and it looks pretty strong. I wonder what is making it so low of hp.

[T@BD]

They'll hold much more than 11hp. I'm planning to use our GY6 reverse gearbox on my 32hp Crossfire build.

Take a look:

http://buggymasters.com/forum/showthread.php?t=6259

There is no rating from the manufacturer, but they're tough.

[fan4chevy]

Travis,

Been looking over your site for some time. Will be supporting you on you site for parts. You have one of the nicest sites.

After looking at your topic on your build, boy you are quite a craftsman. Incredible welding and mill work.

On the reverse gearbox, are you needing to do any mods to it or fab work to get it to hold that much horsies?

What are you using on that engine for the transmission?

I have been looking into silverwing 600's and Yamaha 400 scooters as an option for swap. Not sure yet if I will move this route or back down to big bore gy6 with 2-3mm stroker.

[BEEFKING69]

Im also using a gy6 reverse box on my 400 swap as ive decided the polaris tranny is going to be to bulky. Hondamatic 400 is 30hp stock and when i do the cb450 head and cam swap itll be at 45hp then whatever the fuel injection swap adds. And i still think a 250 or bigger would better than dumping alot of money in a 150 although i want a tadia 232 just to say i built one.

[fan4chevy]

Beefking69,

I had considered the 232 taida until I did research and found that it has no reliability. I had found that it is strictly a race engine with designed to go down the track and shut down.

Regarding the reverse gear box, I would assume one issue will be that not all engines are going to have the same spline as the gy6 150. The other part is can the parts inside truly hold up against so much more torque and power.

[BEEFKING69]

If you go read my build thread you will see how im going to use it. And i believe they will since planetary gears are strong just by the way they are built. I broke one on my highly modded crossfire 150 but it was because i ran it dry and full of mud :/ I broke all 3 sun gear post off the backplate but had them re welded and never had anymore problems. I also want to convert mine to a moorse type cable in stead of the normal cables since i use reverse way more than a normal person i was constantly breaking reverse cables before the Hammerhead rear section transplant.

Thats good to know on the tadia kits as ive never really researched them since they are so costly.

[fan4chevy]

Beefking69.

Regarding research on Taida, it is not recommended to go past the 180cc model for reliability. So all the expense would be worthless if that is the case.

Do you have a link to the thread you are referring to on your build?

[BEEFKING69]

Thats good to know and here you go. http://buggymasters.com/forum/showthread.php?t=6161

[fan4chevy]

Beefking69,

Thanks for the link.

I wonder if the splines are different or the shaft is too short on the new engine to be swapped if it can be cut and welded to the gy6 shaft to get the reverse box to fit properly?

[BEEFKING69]

You want a chain drive motor and you dont do anything to the motors shaft. Its going to be a jack shaft with a reverse box on it.....so in my case im going to have a 1 inch keyed shaft bored out on one end and have the reverse shaft pressed in and welded....then ill have a chain from the 400cc to a 30tooth sprocket on the left side of the shaft then the reverse box on the right side with a chain from it to the axle.

[fan4chevy]

what is a jack shaft?

[BEEFKING69]

For instance in my case and your case if you was to use a motorcycle motor the sprocket is on the left side of the motor and since the axle sprocket is on the right side of the axle we will have to have a shaft with with a sprocket on both sides in order to connect our chains and that shaft is called a jack shaft. So you will have a chain going from the motor to the jackshaft on the left then on the right another chain that goes from jackshaft to axle......Hope that made sense

[fan4chevy]

Now that makes full sense.

[T@BD]

Originally Posted by fan4chevy

Travis,

Been looking over your site for some time. Will be supporting you on you site for parts. You have one of the nicest sites.

After looking at your topic on your build, boy you are quite a craftsman. Incredible welding and mill work.

On the reverse gearbox, are you needing to do any mods to it or fab work to get it to hold that much horsies?

What are you using on that engine for the transmission?

Thanks Chevy!

The plan right now for the gearbox is to leave it unmodified internally, ride on it, and see what changes need to made along the way. The Ninja 250R engine has a manual 6-speed transmission built in.

I plan to use a jackshaft and chains setup between the engine and gearbox, same as beef described. I have female splined couplers that mate to the reverse shaft.

Not sure yet if I will move this route or back down to big bore gy6 with 2-3mm stroker.

If you decide to go big bore / stroker, let me know. Most advice I see online is from guys that have built and blown a couple without much success making them reliable. Trial and error gets expensive after a few attempts, so there is a big gap in between what's common knowledge right now versus what is actually possible with the parts.

I've gotten the 62mm bore x 60.8mm stroke with 10.35:1 compression very reliable on the generic GY6A case without any expensive Taida parts. Just better building and machining techniques developed over a lot of failed attempts. My oldest engine with this setup was built in 2012 and still running flawlessly with zero issues, and starts up on the first touch of the key, faster than a new 150. The one caveat that I haven't been able to resolve is the trade off of a reduced safe redline (keep it under 9000rpm). What you give up on the top, you more than make up in gobs of low-end torque.

The black buggy in my ad at the top of the site shows the difference in torque over stock. Helpful to get up and over steep terrain.

[fan4chevy]

Thanks Travis.

Did you make those splines?

If I needed a custom small sprocket made for an engine that has different spline than gy6, can you do it? If so, any idea around bout what it would cost?

[T@BD]

Originally Posted by fan4chevy

Thanks Travis.

Did you make those splines?

Fortunately no, broaching splines is a real pain. We were able to convince the factory that makes Yerf Dog sprockets to sell the splined collars to us separately.

Originally Posted by fan4chevy

If I needed a custom small sprocket made for an engine that has different spline than gy6, can you do it? If so, any idea around bout what it would cost?

I might be able to. Are you talking about using a sprocket blank and/or existing hub, or machining it all from scratch?

[BEEFKING69]

What are those collars for? I have ordered a 1"x12" keyed shaft and have a reverse box shaft....would you be able to mate the two together for me and if so how much? Ive still not found any one local to do it altho i have some leads but havent actually talked to anyone

[T@BD]

Originally Posted by BEEFKING69

What are those collars for?

They're originally for Yerf Dog GX150 13T sprockets.

Originally Posted by BEEFKING69

I have ordered a 1"x12" keyed shaft and have a reverse box shaft....would you be able to mate the two together for me and if so how much? Ive still not found any one local to do it altho i have some leads but havent actually talked to anyone

If you'll send in a write up with the axle of exactly what you want done so it's a matter of cut here and weld there (so I don't have to design anything), I'll do it for whatever you want to tip.

[BEEFKING69]

A guy named Donnie had this made for his CB400A hammerhead swap and I had been talking to him back in january about his build and he said he would have one built for me whenever i got ready but when i emailed him a few months later about it again his wife informed me that he had passed away .

He said he had the reverse shaft cut down a couple of inches and he had the 1" shaft bored and the the reverse shaft pressed in, trued and welded.....Now whats confusing me is in the finished pictures it appears that its pressed almost to the splines so im assuming that the larger part of the reverse shaft was turned down?Also see no sign of being welded and in the drawings hes got the shaft listed as 3/4 but his parts list all showed 1" stuff. What are your thoughts on this?

P.S. Fan4chevy not trying to hijack your thread but maybe this will help you out also if you decide to go this route

[T@BD]

That's a darn creative solution. I'd be planning to make it at the same time I make my own. How quickly do you need it before it begins to hold up your build?

Based on the pictures, it looks like he took the pic before welding but I can't really tell. The reverse shaft's OD is 3/4", so the keyed shaft it's pressed into must be 1". I agree that 1" is the way to go.

[BEEFKING69]

Im not really sure lol the one inch shaft should be here next week i hope but id probaly say as long its done this month. This is one of 4 buggys we are taking to the races jd's having.

My biggest hold up atm is the fact i cant get the cv cups off the center axle on my crossfire (hh250ss rearend).

[fan4chevy]

This is interesting. I have just seen in a forum unrelated where someone stated to use an electric motor such as a starter for reverse. Interesting thought. Rarely do you use reverse but those few times you need it, it is important. What do you all think?

[BEEFKING69]

Electric starter reverse is really common on the large high powered homemade buggys and using a atv winch has been done but you need a massive gear and its slow and jerky when engaging.....I use reverse alot especially when making trails etc.

[fan4chevy]

Beef,

Do you think that our gy6 one will really be able to hold up on 40 and above hp?

[neo71665]

The electric starter as reverse has been used in production rides. Older golf carts come to mind. Something else you mind find interesting if you don't know is older two strokes sometimes you would have to shut the engine off, push a reverse button, and then the engine would crank backwards for reverse. Going back forward was exact opposite.

I ride in the woods often making my own trail and use reverse all the time. On my trail/mud truck we back out enough stuck I have a winch on the rear of it as well as the front. Electric starter wouldn't have enough torque out there or spin the buggy tires fast enough to keep the lugs clean/grabbing in mud or grab and jump over a stump.

[neo71665]

Originally Posted by fan4chevy

Beef,

Do you think that our gy6 one will really be able to hold up on 40 and above hp?

Worse you can do is try it. I'm sure it'll be fine as long as you aint banging on it or trying to do stunts driving backwards.

[BEEFKING69]

I think it will.....I hope it will....Guess we will find out soon. Donnie never had any problems with his and he beat the %$&*# out of it. Only failures ive seen are my old one from being full of mud and some with broke teeth from people slamming them in reverse and hitting the gas without it being fully engaged.

[fan4chevy]

I took one apart and the gears looked very thick and strong. I think as long as we don't mash in when in reverse should hold up. The forward gear and shaft looks thick and strong as well. If anything I would think the outside casing is the weak point.

[BEEFKING69]

I had actually thought about telling you to take one apart and check it out but i didnt know if you had one on hand.

[fan4chevy]

I have 3 of them. I am looking to put in a 500cc scooter engine. So I guess if I can get it somehow to hookup, I can see how it holds up. I am going to look to see what weak points there are.

If it does not work, I might try the electric motor reverse being that backing up is not too common.

[BEEFKING69]

Travis i got my 1" shaft today so i can send both to you when ever.

[T@BD]

Originally Posted by BEEFKING69

Travis i got my 1" shaft today so i can send both to you when ever.

Sounds good, just PM'ed you our shipping address.