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JC766 02-14-2020 02:10 PM

Driver to small for 7” Driven
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I thought I would add a 7” driven to the Kart for increased torque because of the big 22” tires and heavy frame. It works great however I am limited to about 3,000 rpm because the belt will climb above the small primary clutch. I should have thought about this considering an ATV clutch uses the same size driver and driven so they as the belt transitions between the sheaves it is taken up by the opposing side.

So, is there a bigger drive clutch? Has anyone used a 7” before on a 30 series’s day had the same issue? Even with the 6” why would they not make both sheaves the same size?

anickode 02-14-2020 05:40 PM

Do you have the right belt on it?

itsid 02-14-2020 07:29 PM

uhm judging by the picture alone.. the belt appears to be the wrong way around..
the series 30 uses an asymmetric belt after all
I mean it clearly says : "this side towards the engine" and yet the arrows are pointing in the opposite direction ;)

just a wild guess, but maybe flip the belt and see how it does, right ;)


vpd66 02-15-2020 08:32 AM

When you change to a 7" driven you have to change the engine centerline to jackshaft centerline and make sure you have the correct length belt. You just can't put the 7" driven in place of a 6" and use the same belt. If you go to Comet's website they have a chart with dimensions on shaft spacing, clutch size, and belt size.

Bansil 02-15-2020 08:48 AM

Itsid...moar graceful than I :cheers2:

anickode 02-15-2020 09:22 AM

Out of curiosity, why did you change the driven pulley instead of just doing a sprocket swap?

If you went for example, from an 18" to a 22" tire, that's a ~20% increase. So you go from let's say, a 72 tooth sprocket to something around 86 teeth. Not saying these are your actual numbers, but you get the general idea.

JC766 02-15-2020 10:10 AM

Wow. Disgraceful. The belt is backwards. I was so frustrated with trying to preload the clutch that I forgot about the belt. I saw two videos, one said rotate 180 degrees for preload and the other said a quarter turn. The 180 degrees was definitely not working. The spring would be wound to tight and the clutch would not operate properly. So I finally gave up on the third hole and just used a quarter turn preload with hole #2.

It has 8T on the jack and 60T on the sprocket. I didn’t want a bigger sprocket so changing the ratios of the TAV unit seemed to be the better route to get the extra torque needed for the bigger, wider, and heavier tires.

itsid 02-15-2020 10:55 AM

well preload is ALWAYS one valley on the cam
those are 120° apart.. so neither 90° (quarter turn) nor 180° (half a turn)
is actually a good rule of thumb;
it's dead center in between (120° one third of a turn) ;)

Anyways, one valley is what you should remember since that holds true for all of them.
no mater what hole, no matter what TC (series 20, 30, 40... even most larger ones)

60:8 is only 7.5:1 ratio that's kindof a stretch with a heavy kart and wheels that big
you kart must be lighter (all passengers seated)
than 265kg / 585 lbs (yes with a series 30 and 7" driven)

with a curb weight of 346 lbs of the Manco Intruder II
that's only 239 lbs of passengers you can move around.

(it's rated for 350 lbs of passengers originally.. to a grand total of 696 lbs)

there's very good reason it only came on 18" low pressure tyres, not 22"s

So yeah... with that ratio, 20" rears is about as good as you can get...
for 22" you need about five more teeth on the axle sprocket
(65/8 makes it a 8.125:1 ratio)

And that only if you really have an 8T TC sprocket and not the original 9T!!


JC766 02-15-2020 11:54 AM

Yes Itsid, you are correct. It is the original 9T on the jack stand (not 8). I mistyped. The tread on the tears is practically brand new. Although the cracks in the tires definitely tells me the tires are 5+ years old. It appeared to have the original comet belt 203589 when I picked it up that looked worn. So from what I have read on this site I knew my gearing was going to be wrong with those tires. So my original thought was new belt and 7” driven to get back the gearing I needed rather than try to find new rims and tires which would be triple the cost of the belt and driven clutch.

I think the ratio should be pretty good now with the bigger driven. On my ATV we make a slight modification to the secondary and get about 20% more low. Increasing the diameter of the driven by an inch should be easily a 1:3 ratio now with a final ratio I have read of 1:1.4

I’ll fix the belt and see how it performs and see if it still rises above the drive clutch

itsid 02-16-2020 07:11 AM

with a nine tooth TC sprocket you'll need a 74T axle sprocket (WITH a 7" driven!)
for 22" rear wheels

11 teeth less than you'd need for a 6" driven (85 Teeth on the axle sprocket)

So no, you will NOT be good I'm afraid.. unless you entirely remove the passenger seat,
you'll always run into an issue.


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