What type of clutch do I need?

[FarmerKarter]

Hello. I am restoring an old gocart and using a spare engine I had - GX390 with 2:1 reduction gearbox. I'm almost finished and it will drive direct but I want a centrifugal clutch for my kids. I have purchased a clutch online but it is not engaging even at full throttle.
The GX390 spec says max 1800rpm shaft speed at full throttle with the reduction gearbox.
Does anyone know a suitable clutch that can be used in this scenario? Any other advice? The kids are getting impatient!
Thank you.

 

[Sparkwizard]

@JimD would know if anybody does.

 

[JimD]

It will not work because it cannot spin fast enough to throw the shoes out and lock them to the drum. Even if you took out the spring there isn't enough centrifugal force to lock up the clutch it would slip and turn red hot and you would be able to cook your dinner in the clutch drum. Looks like the shaft size is 1" with a 1/4" keyway which is going to be another challenge. You will be better off putting that engine back on the shelf for another project and getting another engine with a 3/4" crankshaft so you can put a t/c on the kart. Cannot see the tire size but I am guessing they are bigger than 13" in diameter which tells you,THINK TORQUE CONVERTER.

 

[Hellion]

The reduction gearbox “looks” modular as if it can be unbolted and cast aside. What is behind it in regards to the engine’s actual PTO/crankshaft? (<— I am asking the learned elders of the forum).

I suppose another 1” shaft with a gear on it that is affixed with a key and bolt; I am not sure but I am prepared to be quite wrong. The assembly may not be user modifiable. Depending on that and the kart, you might get by with that centrifugal clutch and chain drive…..

Like JimD alluded to, show us photos of the kart and its rear tires.

 

[FarmerKarter]

It will not work because it cannot spin fast enough to throw the shoes out and lock them to the drum. Even if you took out the spring there isn't enough centrifugal force to lock up the clutch it would slip and turn red hot and you would be able to cook your dinner in the clutch drum. Looks like the shaft size is 1" with a 1/4" keyway which is going to be another challenge. You will be better off putting that engine back on the shelf for another project and getting another engine with a 3/4" crankshaft so you can put a t/c on the kart. Cannot see the tire size but I am guessing they are bigger than 13" in diameter which tells you,THINK TORQUE CONVERTER.

Hi JimD, not what I wanted to hear, but thanks for the feedback. Yes correct it is a 1" shaft and 1/4" keyway. Why would I not be able to install a t/c on the 1" crankshaft? But it would work on a 3/4"? Is it purely chasing a faster shaft rpm?
Perhaps a smaller engine would suit then with a 3/4" shaft and t/c. Maybe circa 8hp rather than 13hp?
Would a clutch work on the smaller crankshaft? I'm sure I had a clutch in the last version of the gocart with a 6hp engine 3/4" shaft.

 

[Hellion]

You need the full RPM range of the engine to have fun. 1800 revs from the gearbox final drive, even if it were able to make the clutch engage, won’t be fun for anyone much less kids that enjoy rollercoasters and thrills. You need to “uncork” and uncouple that engine from its gearbox.

3/4” is basically the industry standard for clutches and T/Cs. There are 1” T/Cs though but I wish Max Torque made one.

 

[Sparkwizard]

I bought a couple of Honda 390 engines from a guy who took them off of concession karts after the track closed. They had gearboxes that looked like this one. They had wet centrifugal clutches in them with 2:1 gear reduction and 20mm crankshafts.
Does this engine have a clutch inside the gearbox? Can you turn the shaft that comes out of the box?

 

[Edwin Spangler]

Im very interested in more info on that gearbox...

 

[Denny]

Im very interested in more info on that gearbox...

You can buy a wet clutch 2:1 reducer box at the Jungle Store.

Hi JimD, not what I wanted to hear, but thanks for the feedback. Yes correct it is a 1" shaft and 1/4" keyway. Why would I not be able to install a t/c on the 1" crankshaft? But it would work on a 3/4"? Is it purely chasing a faster shaft rpm?
Perhaps a smaller engine would suit then with a 3/4" shaft and t/c. Maybe circa 8hp rather than 13hp?
Would a clutch work on the smaller crankshaft? I'm sure I had a clutch in the last version of the gocart with a 6hp engine 3/4" shaft.

1800 rpm is too slow for clutches or CVTs to work period. End of discussion on that matter.
You’ll need an engine that will rev to 3600+ rpm for a centrifugal clutch or a CVT to work. Then the fun starts! It doesn’t matter what engine size you choose 212-670 as long as it has a 3/4” output shaft for a centrifugal clutch or 3/4”-1” for a CVT we can help you make it work. BUT THE OUTPUT SHAFT MUST BE ABLE TO SPIN 3600 RPM MINIMUM!!!

 

[JimD]

We all would like to see what size tires are on the kart because that will tell us if a clutch will work or not. Large tires are for t/c not a clutch. Also the gear you have right now on the clutch you bought is wrong. 6 x the # of teeth on the clutch would tell you the size of the rear sprocket you need but ONLY if the tires are 13" or less in diameter. Clutch looks like it has #35 chain teeth but just guessing.

You will get a lot of good advise on this site but we don't know yet how mechanical you are but before you are done you have the best super mileage vehicle built. Tesla is always look for good engineers and this site will be giving degree out in a few year.

 

[Edwin Spangler]

You can buy a wet clutch 2:1 reducer box at the Jungle Store.

Oh ok, I didnt realize it was such an off the shelf bolt on. I thought it was some mythical Manco gearbox or something.

 

[Denny]

Nope, Honda rip off part actually.

 

[Hellion]

Found some matches for the engine and gearbox combo; the GX390 K1 "H" and "L" series.
H series is 6:1
L series is 2:1

https://www.hondalawnparts.com/honda-gx390-engine-parts

Either way, it appears to be simple gears, no clutch unless there's more info out there...

Oh ok, I didnt realize it was such an off the shelf bolt on. I thought it was some mythical Manco gearbox or something.

The aftermarket bolt-ons seem to consist of this configuration:

 

[Hellion]

I wanted to know if you can take the gear reduction module off that GX390 and have a "regular kart engine" underneath. My web searching skills (amateur rank) did not find much of anything.

Maybe someone else knows if it can be done without major mods or cost?

Show us your kart and the size of the tires, Farmer

 

[Sparkwizard]

I bought two engines from concession karts after the track closed in the early 90's. The Honda 390 engines had wet clutch 2:1 gearboxes on them. When I removed the gearboxes, they had 20mm straight shaft, with keyway and were drilled and tapped.

 

[Denny]

I wanted to know if you can take the gear reduction module off that GX390 and have a "regular kart engine" underneath. My web searching skills (amateur rank) did not find much of anything.

Maybe someone else knows if it can be done without major mods or cost?

Show us your kart and the size of the tires, Farmer

No because of the odd sized pto shaft 20mmmm.

 

[Hellion]

No because of the odd sized pto shaft 20mmmm.

Well we don't care about that. Quit yer stinkin thinkin' that everything has to be SAE. bro.
JimD even offered (another guy in another thread) to make a 20mm centrifugal clutch and presumably he can also make a 20mm CVT (driver) clutch....

 

[Denny]

Well we don't care about that. Quit yer stinkin thinkin' that everything has to be SAE. bro.
JimD even offered (another guy in another thread) to make a 20mm centrifugal clutch and presumably he can also make a 20mm CVT (driver) clutch....

But he only builds 20 series CVTs. So I stand by my original statement!

 

[JimD]

Hellion, I can do some things but making a 20mm CVT (driver) isn't one of them. The problem there is the 4 lobe piece that the driver slides on is heat treated (hard as wedding night -ick) and it has a built-in-key so there is NOTHING I can do about that piece. As one person pointed out it is fairly easy with a flapper disc to take the crank down the needed .037 (.0185 a side) and you have your .750 crank and then you are not dependent on anyone to make you a special. It is amazing how quickly the crank will turn down so keep stopping the engine to measure the crank. It is even harder to add material back if you take it down to far.