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Old 01-08-2020, 02:59 PM
Johndeereman Johndeereman is offline
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Default Belt/Chain combination slipping

Just bought this little go kart. Has a pretty big 13hp Honda that looks like someone hacked on there. I'd like to keep that on, but the belt keeps slipping and wearing out. When I bought it, the tensioner would loosen immediately and not work - so I put the large bolts on the back to snug it up tight. No matter how tight or loose I make it, the belt slips and burns up. I've replaced it twice now which it works decent when new, but wears quick.
Any suggestions on making it not slip? Convert to completely chain somehow?
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Old 01-08-2020, 06:27 PM
Smerft85 Smerft85 is offline
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I'd consider removing the belt and pullies, you can get a 14t sprocket for #40/41 chain, and calculate what size you'd need for the sprocket on the jackshaft, likely a 9t or 10t depending on the other two sprocket tooth counts and tire size. The 14t centrifugal clutch on Amazon was the cheapest option I found for a 1" shaft, which your gx390 honda has. This will probably be your cheapest option, a 40 series tav unit is pricey, you can do the clutch, sprocket and chain at least twice over for the cost, and a 30 series won't even mount up to the big blocks, or hold up very long if you do cram one on somehow.
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Old 01-08-2020, 06:32 PM
Johndeereman Johndeereman is offline
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Sweet thank you. Does it make sense to do the chain to chain combo, or would it somehow be better to move the engine over and do a direct drive? I'm decent at fabrication to do so, just don't know anything about go karts/the mechanical technicalities of that
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Old 01-08-2020, 06:32 PM
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JTSpeedDemon JTSpeedDemon is offline
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The reason you're burning up belts is because your gearing is much too high. Even eyeballing it, it's obvious. Belt driven karts need bigger axle pulleys than an equivalent roller chain sprocket.

The cheapest solution would be to get a chain clutch and axle sprocket.
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Old 01-08-2020, 06:37 PM
Johndeereman Johndeereman is offline
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Gotcha. It probably sounds obvious in your mind... I just have no experience with gearing so I really appreciate this information. I'll definitely look into chain and sprocket now
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Old 01-08-2020, 07:26 PM
Smerft85 Smerft85 is offline
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That's what we are here for, I didn't pay attention to much more than what would be easiest to get rid of the belt, but JT Saw what I didnt, correct the gearing as he said and it will do much better, the chain drive will be a huge improvement as well. If you Google a go kart gear ratio with a jackshaft calculator you can play with the tooth count of your jackshaft sprockets and see what you'll need to approach a 6:1 ratio, count on a 14t clutch unless you go tav, and count your wheel sprocket teeth, those two numbers will stay the same, play with different tooth counts for only the jackshaft, that's how I got mine just about right, one less tooth and I'd gain bottom end torque and lose a little top end speed, which I may still do on mine.
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Old 01-08-2020, 07:32 PM
mckutzy mckutzy is offline
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You want to aim for a 6:1 ratio...here's a calc...
https://affordablegokarts.com/pages/...tio-calculator

Now with that being said... you have a big block motor.. That'll typically have a 1" shaft....
If you go a cent clutch route... it will be expensive....

I know there is a TC that fits the 1" shaft motors... but Im not too sure offhand the type, or also if itll fit with out a driven jackshaft setup...
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Old 01-08-2020, 10:36 PM
Johndeereman Johndeereman is offline
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Ok thanks for all the help. Just ordered 14T clutch that claims it can handle 13hp - I have read a lot saying my engine is too big for 14t's but at $20 I'll try it. Then another sprocket and #40 chain.

The closest ratio I could get on the calculator with the available sprockets is 5.5. I assume that's close enough to 6?

Here's the clutch that I ordered:

https://www.ebay.com/itm/Centrifugal...ry!02806!US!-1
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Old 01-08-2020, 11:34 PM
Smerft85 Smerft85 is offline
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Quote:
Originally Posted by mckutzy View Post
You want to aim for a 6:1 ratio...here's a calc...
https://affordablegokarts.com/pages/...tio-calculator

Now with that being said... you have a big block motor.. That'll typically have a 1" shaft....
If you go a cent clutch route... it will be expensive....

I know there is a TC that fits the 1" shaft motors... but Im not too sure offhand the type, or also if itll fit with out a driven jackshaft setup...

Centrifugal that will fit the 1" shaft on Amazon is like $30, the T/C or TAV unit needed is a 40 series and pricey, if that's a genuine honda gx390 (which it is) it definitely has the 1" shaft, my post above yours is saying almost the identical thing.

---------- Post added at 12:34 AM ---------- Previous post was at 12:31 AM ----------

5.5 ratio is still pretty high, but likely better than what you currently have, the chain shouldn't slip like your belt, however you may have a shorter life out of the centrifugal clutch, it will have less torque or take-off, and much more top end speed, it will just take forever to hit top speed, and forget about burnouts!
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Old 01-08-2020, 11:44 PM
Smerft85 Smerft85 is offline
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Sorry for the slight threadjack, but this is pretty much my home made setup how I'm describing setting yours up, it's pretty similar, gx270 honda big block, 1" shaft, 14t centrifugal clutch, jackshaft sprockets both in and out the down to your drive sprocket, that's a $30 Amazon clutch. I still need to lower my ratio, and if I change just one tooth count on my jackshaft I can get a higher or lower ratio without touching anything else. I hope it helps out.

EDIT** I just noticed it looks like only two of the four bolts needed to bolt the engine down are present, I bet you aren't even getting the tension on the belt you thought you were when the engine puts down any power, my gx270 has enough torque it bent 1" square tube steel, I bet a gx390 has at least comparable torque ratings.
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Old 01-09-2020, 01:37 AM
madprofessor madprofessor is offline
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Default HVACR expert eyeballing your pulleys....

I've replaced literally hundreds of pulleys in my career in HVACR because they were worn out, so I know what looks bad. Most people don't believe that a rubber belt can survive while a steel pulley wears away, but it's true.
Both of your pulleys look worn out to my experienced eye, and that would mean belt slippage you can't stop. The reason is that a V-belt is supposed to ride on its sides on the sides of a V-groove, not on its belly down in the bottom of the groove. The belly should never even graze the bottom of the groove.
It happens because the slanted sides of the pulley wear away and become straight drop-offs, landing the belt on its belly, which has very little grab at all.
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  #12  
Old 01-09-2020, 06:08 AM
Johndeereman Johndeereman is offline
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Quote:
Originally Posted by Smerft85 View Post
EDIT** I just noticed it looks like only two of the four bolts needed to bolt the engine down are present, I bet you aren't even getting the tension on the belt you thought you were when the engine puts down any power, my gx270 has enough torque it bent 1" square tube steel, I bet a gx390 has at least comparable torque ratings.
Yes haha the guy who put that engine on must've been a huge hack. Engine isn't close to stock engine mount. I'll weld something up to catch the other bolt holes. I'll also order another sprocket with more teeth so I can switch em out on the go between speed and torque

---------- Post added at 07:08 AM ---------- Previous post was at 07:06 AM ----------

Quote:
Originally Posted by madprofessor View Post
I've replaced literally hundreds of pulleys in my career in HVACR because they were worn out, so I know what looks bad. Most people don't believe that a rubber belt can survive while a steel pulley wears away, but it's true.
Both of your pulleys look worn out to my experienced eye, and that would mean belt slippage you can't stop. The reason is that a V-belt is supposed to ride on its sides on the sides of a V-groove, not on its belly down in the bottom of the groove. The belly should never even graze the bottom of the groove.
It happens because the slanted sides of the pulley wear away and become straight drop-offs, landing the belt on its belly, which has very little grab at all.
Oh I didn't know that, but it makes total sense. Already ordered the chain replacements, but if it doesn't work out I'll go grab some new pulleys and try that. Thanks
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