Newbie Help Choosing Clutch For New Engine

[smu1290]

I am new to this forum and I hope Iam posting im the right area.I have a old murry go kart with a 6.5hp tucumson engine with a 3/4 output shaft. I believe it has a jackshaft, but im not sure that what i think isa jackshaft isactually a jackshaft. Please read and let me know if im right.

The clutch sprocket is 10 (on engine), jackshaft input is 25 (from engine to jackshaft). The output is 10 (to the axel) axel 35. According to the ratio equation its 9.6:1, I think. It has 16 in rear tires.

Currently drive on packed sand and road but I wish to drive off road on loose sand up and down hills.

I just bought a clone 11hp engine with a 1in output shaft from harbor freight. I figure I have to change out the clutch for a 1in.

For my desired driving would it be better to convert it to a torque converter or stay with the centrifigul clutch? If I switch how hard is it to switch? What type should I get?Any help would be greatly appreciated.

 

[OzFab]

First off, your final ratio is 8.5:1, not 9.6:1, which is a good ratio with 16" tyres.

However, for driving on hills, you're always better off with a torque converter but, to fit a 1" shaft, it's gonna set you back around $300; even a cent clutch will cost you around $150...

Setting up a 40 series cvt isn't "hard" but will probably involve a bit of fabrication. Also, if you stick with your current setup, you will end up with two jackshafts

 

[smu1290]

Why would I need 2 jackshafts?

 

[OzFab]

Why would I need 2 jackshafts?

Because you already have one & the CVT driven rides on another...

 

[Doc Sprocket]

No need for two jackshafts. Either keep the existing, while employing a centrifugal clutch, or get yourself a CVT (Comet 40 is best choice) and either re-use the existing shaft (if possible) or engineer a new one to suit.

My "if possible" comment is based on the fact that a CVT requires very specific "On center" spacing between the drive and driven units. The Comet 40 uses a range of belt sizes- which gives you a range of spacing. If yours fall within this range, you're good to go. Do note that if you go this way, you WILL have to get a new, larger rear sprocket. If you stay with a centrifugal clutch, you can likely keep everything as-is.

 

[smu1290]

Okay, what is the spacing for a CVT and how big of a sprocket do I need?

 

[Doc Sprocket]

Here's a chart- http://www.gokartsupply.com/beltchart.htm Scroll down to Comet 40, and check the Center Distances.

As for the sprocket, the bigger, the better. We don't yet know how big your rear tires are, or what your chain pitch is. Shoot for 72T, bigger if possible.

 

[r_chez_08]

Hi,
In order to mount a comet 40 with your existing kit, the distance between the centre of your jackshaft and the centre of your engine crankshaft must be between 7 1/4" and 15 3/16".
See thishttp://www.gokartsupply.com/tcbelts.htm link.

Also, make sure the jackshaft is of a correct diameter, with a suitable keyslot. You also need plenty of clearance around the jackshaft and engine for the pulleys.

I would recommend a 60t rear axle sprocket. You will have a substantially higher top speed than with your old setup and you should also have plenty of torque with the comet 40 torque converter. A 60t sprocket is also a common size, and heavy duty steel one is reasonably cheap on bmi karts.

Make sure that when you order up the new sprocket that you get one with the same pitch as your old gear. You may also consider replacing your old jackshaft sprocket and chain if it is substantially worn, because when mixing worn and new sprockets and chains, the new kit tends to get worn out more quickly.

Finally, if you haven't mounted your new engine yet, bear in mind that it will probably have a larger footprint with a different bolt pattern than your old engine. You may need to adapt your mounting plate or buy or fabricate a new one.

Cheers,
Rob

 

[smu1290]

My tire size is 16 in from ground to top of the tire.

My sprockets are 1/2 in from the center of one tooth to the other, what is the chain size?

I beleive my jack shaft sprocket is part of the shaft attached are some photos, do Ineed anew jackshaft?

 

[r_chez_08]

Sounds like #40/41 chain to me. Do a forum or Google search on chain pitch.

Yeah it looks like the jackshaft sprocket is welded on. A new jackshaft is fairly cheap though. I find bmi karts great for bits like this.
That sprocket and chain look fairly thrashed anyway. What's with the kinks in the chain?

It's hard to tell if you could fit a 40 series in there, but I think you will manage. More pics would be useful!

 

[smu1290]

I believe the chain is a 40. The jack shaft mount is adjustable. I think I will replace the jack shaft with a new one and a larger driven sprocket. I have a new chain for it. Thanks for all the help.