Clutch and Gearing

[laharview]

Hi All,

Helped my Son build a Cart frame, this is a first attempt for both of us. As you can guess the engine (6.5 HP Tecumseh) will not RPM up and poor power. Using a 12T Comet clutch with a 72T sproket and the tires are 21" tall.

1. We bypassed the govener and the engine idles poorly, adjusted so we have a good idle and the clutch is hooking up. Is there another brand of clutch (3/4" shaft) that hooks up at a higher RPM?

2. Is there a source for a sproket with more that 72 teeth?

I have thought about building a jack shaft but am not sure where to start with the sproket sizes. Also smaller rear tires but that kills the look he was going for.

Thanks for any advice!

Mike and Gordon

 

[osufans]

I'm no expert on these at all, as quite frankly, I'm pretty new to the kart scene. However, that setup looks outrageous. I did a quick search and found that indeed, different clutches engage at different RPM's, so that could be one thing to look at.

However, another thing I read suggested that for circumstances like yours, where you have a lower HP motor, with larger diameter tires, you may have to look into a belt/pulley system.

**There are many variables that play into the performance of a clutch. Tire size, rear sprocket size and rear drive set-up are a few of the main variables that could affect clutch performance. If you are using large tires or a small sprocket, your vehicle may require a belt drive system. Clutch performance is not based soley on the engine size.**

I'm sure someone with more experience will chime in...but I would start looking at a belt system anyways. The gearing that would be required to overcome your power loss would cause you to have a really low top speed, which I'm sure would be another disappointing factor for your son.

 

[Badot]

You're geared for a little under 40 mph at 3600 RPM... with a 6.5 HP engine and centrifugal clutch that's probably too fast for even a light kart on a flat road.

Did the engine idle okay before you bypassed the governor?

Also, economy clutches will generally engage at around the same RPM (usually a little over 2000 iirc)... you can get more expensive ones where you can adjust it, but for a kart like one you have it's probably not worth it.

If your clutch is engaging significantly before that, your clutch springs have probably been heated and stretched to where they won't pull the shoes back in enough at idle (which is likely to happen if you run gearing like you have for a while)

If your engine can't reliably idle below 2000 rpm there's something wrong with it.

 

[r97]

At this point I would suggest either a jack shaft or a torque converter. You would need a very big/expensive/impactical sprocket to get the right ratio without a js.

Right now its like driving your car in 3rd gear(bad for the clutch). A jack shaft will make it more like driving your car in 1st or 2nd gear (more acceleration, but possibly less speed). Then there is the torque converter, a bit expensive ($200), but is like having a full automatic transmission with 1st-5th gear, rather than just one speed.

Once you choose whether you want a jack shaft or torque converter your going to need to choose some sprockets. We can guide you towards good sprocket sizes once you choose the system you want. Are you riding off road?

As far as the higher rpm engagement clutch, I don't think it's needed. As long as your clutch hasn't been damaged (with a gear ratio like yours it could have been) you should be able to get your engine to idle low enough. The carburetor might be gummed up, or you just need to let it warm up a bit more.

 

[r_chez_08]

What chain are you running?
You have 4 main choices:
Regear
Smaller tyres
Bigger engine
Torque converter

 

[laharview]

Thanks for the replys,

We started with a craigslist gocart and ended up using only the engine, clutch and seat. The clutch is a bit blue so I gussing the springs are toast.

The engine idles O.K with the govener but hunts a bit. The carb is clean but doesn't have any fuel/air adjusting screws. Engine is 2 years old with low hours.

The chain is #35. We are thinking of the jack shaft due to space and cost and would like help on the gearing. This will mainly be off road so a high top speed in not needed.

Best Regards,
Mike & Gordon

 

[Mrpinhead11]

i wasin ur shoes a couple months ago. i thought the clutch would hold up but it didnt. within a day of ridding in my yard. i bout a torque converter and now i can pop wheelies!

 

[r97]

Ok, what top speed are you looking for?

You may need a new clutch, although the one you have might be decent. Those Tecumseh 6.5 "power sport" engines aren't the best..... although it should work pretty well if maintained and allowed to warm up for a while.

 

[TorqueRanger]

Best bet find a cheap torque converter and go form there.. I will post a link up for you about the limits of a clutch..
Read this part-Centrifugal Clutch Tips
Driving Habits That Can Ruin A Clutch

http://www.gokartsupply.com/tips.htm
or
4) Changing the size of the tires. Putting on tires that are larger than what came with the kart will result in clutch problems. Tires exceeding 13" in diameter stress out a clutch if the kart is not properly geared for the larger tires. If you are driving on smooth flat terrain than you may be able to get by with 14" tires but once you get on hilly terrain, deep grass, then you are putting additional strain on the clutch, which will cause premature wear. Big tires look cool on a go kart but you create your own problem changing to a bigger tire when the clutch isn't designed to handle them. If you have tires over 15" tall you are required to use a torque converter instead of a centrifugal clutch. Do not install rims larger than six inches if your go kart is equipped with a centrifugal clutch.

 

[laharview]

Thanks for the great info. The cart buy was a bit of an impulse buy but for $200.00 I thought "what could go wrong, it has a newer engine"!! So, we ended up with a real nice seat and a pair of aluminum pedals out of the deal.

Gordon is not to concerened about going real fast, just crusin' around the farm. Any good leeds on a converter? Or we may elect to go with smaller rear tires.

Back in the 70's I built chassis and we bolted up blown 426 Hemi's feeding on nitro meathane so gearing was no big deal when you had 2,000 HP to play with.

Thanks Again and Happy Holidays To All,
Mike and Gordon

 

[r_chez_08]

http://diygokarts.com/vb/showthread.php?p=181770#post181770
You should be able to pick up a tav30 or tav2 kit for under $150. BEWARE OF FAKES!!!
This should bolt up with little modification.

A jackshaft and sprocket with a new clutch may be close to $100.
New rims and tyres and possibly hubs could be up to $100
for $150 (yeah its kinda alot) you could keep your current chain and rear sprocket.

Here is an 83t sprocket
http://www.bmikarts.com/item/35-Premier-Split-Sprocket-81T-83T-sale-2142
Only $5. it may be worth getting one of them with your tav. 12:72 is quite steep with any clutch when you have 22" tyres.

 

[laharview]

Thanks, great info!!

 

[landuse]

You could always try a 10T clutch as a starting point. You will then have a 7.2:1 ratio instead of a 6:1. It is maybe worth a try, but I have to agree with all that has been said above.

 

[TorqueRanger]

http://diygokarts.com/vb/showthread.php?p=181770#post181770
You should be able to pick up a tav30 or tav2 kit for under $150. BEWARE OF FAKES!!!
This should bolt up with little modification.

A jackshaft and sprocket with a new clutch may be close to $100.
New rims and tyres and possibly hubs could be up to $100
for $150 (yeah its kinda alot) you could keep your current chain and rear sprocket.

Here is an 83t sprocket
http://www.bmikarts.com/item/35-Premier-Split-Sprocket-81T-83T-sale-2142
Only $5. it may be worth getting one of them with your tav. 12:72 is quite steep with any clutch when you have 22" tyres.

This seems wrong to me because here are my figure for this setup

Gear-
Tav-2 w/6" driven
10t on jackshaft
83t sprocket

Overall ratio-24.73
High speed ratio-7.47
Low speed ratio-22.24


I am going to run about the same setup with the same tire but my setup is heavier than your (not set in stone yet on finally gear ratios)

Tav w/6"driven
10t or 9t on jack shaft (#40 chain because I am a big boy)
60t sprocket

10t on jackshaft
Overall ratio-17.88
High speed ratio-5.4
Low speed ratio-16.08

9t on jackshaft

Overall ratio-19.84
High speed ratio-5.99
Low speed ratio-17.84

 

[laharview]

We are going to try the TAV and have a couple more questions.

- Which model would be the best for our set-up (tall tires)?

- I see how they bolt to the engine but how would the output of the TAV get to the axle sprocket? Photos would be great.

- Could we still use the 72T axle sprocket?

Thanks!

 

[r_chez_08]

1. tav2 or tav30 will be fine. The tav30 has a steel backplate, the tav2 has a cast aluminium plate.
2. there is a sprocket hidden behind the driven
3. 39mph @3600rpm is a bit steep, unless you can find a torque converter sprocket with less than 12t for #35.

 

[r97]

The 9 tooth #35 sprocket on THIS PAGE should do the trick, and allow you to keep the 72t sprocket. Top speed should near 40mph, low end will be geared for 16MPH. You may need to modify the hub, and/or add a spacer to make it fit correctly with the TAV2.

 

[OzFab]

Is it just me or is your clutch on backwards, does that make a difference?

 

[r_chez_08]

With bi directional clutches they can run inboard or outboard, cw or ccw.
Directional clutches can only run one way.

 

[laharview]

Hi All,

This style of clutch works both ways as replied above.

Our engine crank center is behind the axle center so will the TAV work? We can modify the frame (it's only in primer) so the TAV will fit horizontaly. The TAV output center will be further behind the axle, does this cause problems?

Thanks,
Mike and Gordon