Gx390 clutch dilemma

[Danmann]

Hello all,
New member and completely new to go karts, long first post but here we go. I took in this go kart my neighbor has lost interest in and I am stuck on how to proceed. It is fitted with a honda gx390 engine supposedly off a pressure washer per previous owner. It had a 14 tooth clutch on it and the acceleration was horrible from a standstill also the clutch would be red hot after a short time. With the wheels off the ground it seems to accelerate very well and smoothly. So I ordered a 10 tooth clutch only to find out it bottoms out on the crankshaft before I could ever align it with the axle sprocket (60 tooth sprocket btw) so now I am thinking about cutting the shaft to length but would appreciate any other ideas or input on other solutions or ideas from anyone before I pull the trigger on cutting down the shaft. Thanks in advance everyone.

 

[Denny]

That engine has a tapered output on the end of the crank. That is no good. You need it to be straight with a key way. You will not get that to work for you without going and replacing the crankshaft in the engine with a straight one. The second problem is tire size. If you are going to use that size tire you will need to switch to a 30 series CVT TAVII. That is one reason the clutch got red hot.
You could replace the crankshaft in the engine with a straight shaft 1” diameter output crank with a key way and then add a Amazon cheap 30 series TAVII and use a Genuine Comet belt on it.

OR OPTION 2

Remove engine and sell. Buy a new predator of your choice and size and add a Amazon cheap 30 series TAVII CVT and a Genuine Comet belt.

 

[Danmann]

Thanks so much for the reply I appreciate your help. So the shaft does have a keyway not sure if tapered or not but I can measure it. If it is a straight shaft then I would be alright with a torque converter setup like you mentioned. Thanks

 

[panchothedog]

When you say cutting the shaft are you talking about the engine power shaft.
DON'T do that. Measure the I. D. of the clutch you took off. A tape measure or ruler won't work, you will need a set of calipers to get an accurate measurement. From the pictures you posted I am going to agree with Denny.
It looks tapered.

 

[Denny]

On my small phone screen that shaft sure looks tapered. Maybe you could take that clutch off and give us a better picture of the shaft so we could see better.
IF it turns out it is straight shaft with a key way. You just have to figure out if it is 3/4” or 1” and buy the proper 30 series TAVII CVT. The Genuine Comet belt will be the same for both. The Chinese belts that come with the kits or the ones that are cheap to buy do not last and slip.

 

[anderkart]

Your GX390 engine does not have a Tapered output shaft, It has a Strait output shaft with a 1/4" keyway.

Do not cut your output shaft to align that clutch!
The 1"-bore clutch models like yours are only rated for engines up to 7-Horse Power, and will very soon overheat & fail with your 13-HP engine.

Before I make any further suggestions, I need to know:

#1 ~ How many inches tall are your rear tires?

#2 ~ And are the teeth on your 60-tooth axle sprocket spaced 3/8" apart, or 1/2" apart?

 

[Danmann]

Understood, I will take same measurements after work today and report back. I really appreciate all the help

 

[Denny]

Mad, it looks like he is using golf kart rear tires so that would mean they are atleast 18” tall, maybe depending on brand closer to 19”.

Are you using #35 or #40 series chain is what Mad is asking.

 

[Danmann]

Tires are 18" tall, sprocket tooth spacing is 1/2".

 

[Denny]

Ok, your using number 40 style chain and golf kart wheels & tires. Cool, if the engine has a straight shaft you just have to figure out what diameter it is. Take a ruler, tape measure or whatever you have and measure across the shaft to find the diameter. Then order up your TAV II.

 

[Danmann]

It is a 1 inch shaft. Thanks

 

[Denny]

If it has no taper and is a straight shaft, with a key way. You now know what you need to do!

 

[anderkart]

Yep, I agree your going to need a torque converter.

 

[Danmann]

Ok, got the parts ordered I will follow up once I get everything installed. Thanks again

 

[panchothedog]

Danmann, when it comes time to install torque converter on your kart, due to the problem you had trying to install the clutch back when we thought you had a tapered shaft let me offer some advice. I think your clutch just got stuck trying to side onto the shaft, and I can tell you I have had the same problem SEVERAL times, even on brand new stuff. Driver clutches, driven pulley, even the sprocket onto jack shaft that came together in the kit. Get a sheet of 320
or 400 grit wet and dry sandpaper and a little alcohol to wipe it down with after
wards. You'll probably have to do you engine shaft for sure, remove the key and work on the corners of the milled slot as well as the shaft in general. You might also have to work on the inside of the clutches as well. When done wipe everything clean with a damp cloth with alcohol. Apply a light coat of oil or even smear on some grease. 15 - 20 minutes doing this can save a lot of frustration on assembly and if you need to pull it apart in the future it will make it easier then as well.

 

[Danmann]

Thanks for the advice and will do.

 

[Dingocat]

Little late here now. But pretty sure 10 tooth 1in clutches are stepped down at the end as ID of sprocket is smaller than 1", aka why it only went on so far.

 

[Danmann]

Got real busy with my other projects so the kart was on the back burner but I finally got it sorted out. I got an Amazon torque converter kit like suggested and in installed pretty smoothly I did have to weld up the rear oil fill and make a riser for the motor for the chain to clear but so far so good. I appreciate the help once again. And of course not an official update without pics so here ya go!

 

[madprofessor]

That GX390 is rated 13hp. at 3,600 rpm. Isn't that a little strong for an asymmetrical 30 series CVT? I'd trust more in a symmetrical 40 series.

 

[Master Hack]

Gx390 has a 1” shaft. A 30 series TC fits a 3/4 shaft doesn’t it?
I have a gx390/40 series on the buggy and it works well, and its a heavy POS @ about 900 lbs with fluids and driver.