GS750/VW Reverse Trike...Help needed from GS experts!!!

[aaronbev79]

Well, here's my build as it's getting started. My goal is to build something similar to an Rtrike called "Rebirth" except I want to build a one-seater. He uses a type 1 VW font end with a hayabusa motor and rear suspension. Though I plan on doing something more aggressive with my chassis, I like his overall idea.

Since I don't have the money for a sportbike powerplant, I've decided to look for the ever popular 750 motor. Suzuki, Honda, and Kawasaki all made very strong 750s through the '70s and '80s and they are very easy to come by. I found a complete, titled, and running Suzuki GS750 on Craigslist for $300 and snatched it up right away. On the coldest of days it still starts right up, but I will plan on installing a new clutch and cleaning and resynching the carbs.

I also purchased my type 1 front end from Craigslist -- I got a complete front end from spindle to spindle -- with all the steering components -- for $100. It's a little rough, but solid, and I plan on adding disc brakes to it. Here are some pics of type 1 front ends.

Finally, there's my rear suspension. I purchased the entire rear swingarm, wheel, brakes, hardware from a 2000 Ninja 900r for $100 as well. Originally I was going to build my own swingarm and use a really wide drag racing setup, but I decided that it would be outside of my budget to do something like that. And since sportbikes have relatively large rear wheels stock, it'll be easier to use the entire setup as it is -- the Ninja has a 6" wide rear wheel and I can probably fit a 7" wide tire on it. Here's a pic of the exact bike I got the swingarm from:

So now for my questions. First and foremost there's the question of gearing. Obviously I'm going to need more low end to deal with the extra weight, and I'd like to improve acceleration and reduce top-end. So, are there any stock sprockets that can be used as direct replacement to lower my gear ratio? Does anyone know of any aftermarket sprockets that are availble in various sizes for the 78 GS750?

Secondly, there's the issue of the clutch. Obviously the GS750 motor wasn't designed to move around 600-800 lbs of metal, so I'm wondering what all I can do to upgrade the clutch to make sure that I'm not wearing it out everytime I stand on the gas pedal a little bit.

This is a big project, and any advice or critiques is welcomed. Thanks guys!

I'll post pic updates for all my parts and stuff later this week.

 

[salty_monk]

I know a bunch of people running bike engines in Lotus 7 replica's. They use much heavier springs in order to get some feel on the clutch pedal & usually when they've burnt through the first clutch they switch to some kind of heavy duty model.... you're going to go through clutches thought, that's a given.

Dan

 

[Old Colt]

The clutch is the last thing you need to worry about. The rear mounted air cooled engine will overheat well before the clutch is done.
I run a turbocharged Hayabusa in a car with stock clutch. Better part of double the torque and a whole bunch more grip than a bike could dream of. No issues at all.

There are plenty of $300 mid 90s water cooled engines that will have a better time of moving the weight and drag that you will put in front of it.

But then as long as you have great cell phone reception and two good legs and a bottle of water so you can walk long distances then a GS750 should be fine.

 

[spyug]

Welcome aboard. Interesting project you have in mind. I have been thinking of the same thing for the last 4 or 5 years since I first saw the T-Rex. Actually, I always had a love of the Lotus Super 7 and was contemplating building one of the Locost type using a bike engine again until I saw the Rex. That got me thinking a trike build might just be as much fun and maybe a tad easier to construct. So far money and time are holding me back.

For custom sprockets, you can't beat Sprocket Specialists http://www.sprocketspecialists.com/

I had a custom 32 tooth cog done for my tracker to give me more highway speed.They can put you into something that will work for you. Prices and shipping are decent give them a call.

I am going to watch this post with interest so please don't be skimpy on info or pics.

cheers,
Spyug

 

[aaronbev79]

The clutch is the last thing you need to worry about. The rear mounted air cooled engine will overheat well before the clutch is done.
I run a turbocharged Hayabusa in a car with stock clutch. Better part of double the torque and a whole bunch more grip than a bike could dream of. No issues at all.

There are plenty of $300 mid 90s water cooled engines that will have a better time of moving the weight and drag that you will put in front of it.

But then as long as you have great cell phone reception and two good legs and a bottle of water so you can walk long distances then a GS750 should be fine.

Nope -- not accurate.

Actually, most guys who are building DIY reverse trikes use an air cooled engine without any problems. Thanks for the concern, but I have done quite a bit of research on building one of these and I know that I've found a good engine. I thought the GS guys would love the fact that I was using a GS750 for this project, so it seems wierd that you're so negative about a GS750 motor.

I've owned a GS before, and they are tough little motors. Also, I plan on using a side air ducts, and a roof duct to bring more than enough air to the motor. Other guys have used the same system without a problem.

Otherwise, where do I find tougher clutch springs? And what do you guys think as far as gearing? Is there a gearing calculator that you use in order to figure out top end speed in regards to rear wheel/tire size, and front and rear sprockets sizes?

Thanks for all of the help!!!

 

[Guest]

All I can say is kudos to you for doing something different!

I'll be keeping an eye on your progress as I've always had a soft spot for trikes. I don't know why, but it's something that always sits in the back of my mind...

That new Can-Am Spyder looks like a seriously fun bit of kit IMO.

Unfortunately I have no idea on sprockets or clutches to give you a hand...

 

[spyug]

http://www.sprocketspecialists.com/SprocketOptimizer2.aspx

Spyug

 

[spyug]

http://www.barnettclutches.com/

Spyug

 

[aaronbev79]

http://www.sprocketspecialists.com/SprocketOptimizer2.aspx

Spyug

Wow!!! Thanks -- that's just what I was hoping to find in order to do my calculations. Does anyone know where I can find the gear ratios for the '78 GS750 transmission?

 

[mriddle]

Wow!!! Thanks -- that's just what I was hoping to find in order to do my calculations. Does anyone know where I can find the gear ratios for the '78 GS750 transmission?

Here ya go

 

[bonanzadave]

I saw a guy at Bike night in Mpls with something like that.....

 

[lifguardct]

I saw this kit before, can't remember where. It is a ZRX1100/1200 Kaw.

 

[aaronbev79]

If you're really interested in reverse trikes, there's a new forum that was started particularly for this new community of gear heads...check it out: http://reversetrike.proboards.com

 

[aaronbev79]

Here's the look I'm going for -- it's a one seater like the sportcycle pictured below, but it looks more like a supercar or high dollar sports car. It's called the Rayvolution EVO and it's a kit you can purchase in Europe, but I want to make my own that looks like a one of a kind.

And yes, just in case you are wondering -- I am learning all I can about making your own fiberglass body. It turns out, that using creating a basic fiberglass body is VERY simple. I've done a lot of intensive body work in the past on various vehicles that I've built, and working with fiberglass isn't all that different.

 

[fast pom]

Hi mate i race a GS750 good tough engine as mentioned before my only concern may be the clutch there not a bad unit but you are very limeted on the up grades as compared to the 1000 .
All the best with your build

 

[GQROD]

http://www.gearingcommander.com


This is the gearing calculator i used it's good because it goes up to six speed transmissions for ratios.

Hope it helps.

 

[aaronbev79]

Hi mate i race a GS750 good tough engine as mentioned before my only concern may be the clutch there not a bad unit but you are very limeted on the up grades as compared to the 1000 .
All the best with your build

Yeah -- the clutch is certainly my primary concern. However, I'm hoping that lowering the gear ratio will help that quite a bit. Improving my low end should make it much easier for the motor to move the additional weight. However, I figure if I do both -- lower my gearing AND improve my clutch -- that I should be fine...but we'll see.

 

[salty_monk]

If you can get one.. I would put a 1000 or an 1100 Engine in. Why start at 750? You'll get bored with it pretty quick..... I know that from my Lotus 7 replica's.. you always want more power.

 

[aaronbev79]

If you can get one.. I would put a 1000 or an 1100 Engine in. Why start at 750? You'll get bored with it pretty quick..... I know that from my Lotus 7 replica's.. you always want more power.

Well, I've spent more time looking for a reasonably priced engine than anything else with this project. And if there's one things that's true, 1000cc and bigger engines are WAY too expensive compared to 750cc motors. They are used in sprint cars, Locost projects, kits cars, and nearly anything else -- so they go for way too much. Plus, I was really wanting an entire bike because I needed one with a title (for licensing purposes), complete engine, wiring harness, gauges, and frame. At that point, I might as well purchase an entire bike. And finding a 1000cc or bigger bike that's complete and running well is not going to happen for anything near $300 -- I've tried.

I've spent months and months searching craigslist, local junkyards for bikes, ebay, and local classifieds and the GS750 was by far the best deal available. I don't have a lot of money to spend on this project, so I am trying to get the most out of what I have.

As far as power, I've talked with a lot of guys who have used 750cc bikes and they are more than happy with their results. 63hp on a car that weighs 700lbs, and is geared properly, will be more than enough for what I want to do.

Besides, I've already purchased the bike for cheap, and I'm sticking with it for now. If after it's built I am really wanting more, then I will drop in a bigger motor when I have more funds, but for now I am more than pleased with having a GS750.

What I really need are creative ideas for making the GS750 something that will work for this project.

 

[fast pom]

Have a look for some 850 barrels and head just check the stud patters before you buy a cheap way to get some more HP apart from that its time to open your wallet i had some o/s s/steel valves made through Buzz at Dynoman at about $45 each if it still has the points ignition change that for sure Dyna-s is a reasonably cheap straight replacement but speed is a matter of money i am sorry to say,