Torque Converter Help

[Mack2]

First post... Thanks for reading

I am building my son his first kart, also my first kart build... but not my first build.

I have an old Briggs 3hp with a straight threaded 5/8 output. I have the motor apart and was planning on milling a keyway and tapping the end... however I'm having a hard time finding a 5/8 drive torque converter, do they exist, or am I stuck with a clutch? Also, the motor has never been used and its first run was earlier today, It was also free so I'd like to avoid the predator and a cheesiness 3/4 drive converter route.

Thanks again

 

[Budget GoKart]

Well eBay would be your best bet for a 5/8th drive torque converter or you can make it with pulleys and a foot belt engage like a manual clutch like tillers use. I was planning on doing it with a mini bike at one point

 

[Mack2]

I looked on ebay and couldn't find a 5/8 drive only driven?

---------- Post added at 06:40 PM ---------- Previous post was at 06:37 PM ----------

I was also considering turning the 5/8 down and making a 3/4 sleeve that I could weld on. Will the 3 hp have enough to run the 30 series converter?

---------- Post added at 06:48 PM ---------- Previous post was at 06:40 PM ----------

the bearing race is .785, so I can squeeze a 3/4 sleeve in there

 

[Brianator]

I'd recommend against welding the sleeve to the crankshaft, it will ruin the hardening of the steel. You can get a 5/8-3/4" sleeve (with stepped key) on Amazon and other places im sure. If you cut/trim/fit it well, torque the crankshaft bolt and use threadlocker you should be fine in my opinion (pending you turn and tap it as mentioned).

I dont have any experience with 3hp with a torque converter but from what I gather, a clutch and a tall(er) gear ratio would work best.... but I could be wrong. What tire size (height) are you thinking of running?

 

[anickode]

You could probably just use a slip fit spacer.

 

[Mack2]

After sleeping on it, think I'll just go with a clutch as he'll grow out of it pretty quick. I milled a keyway and drilled/tapped for bolt, got it back together and it's ready to rock!

Can you all reccomend a resource for figuring out tire size and gear ratios? I've purchased an 11 tooth cluth so that's where I'll be starting. Thanks for the help

 

[Brianator]

A really great live app for that is at : app.kartcalc.net It takes weight, gearing and tire size (height) into account, tells you approximate top speed and any issues you may run into.

 

[Barnfresh1]

I looked on ebay and couldn't find a 5/8 drive only driven?

---------- Post added at 06:40 PM ---------- Previous post was at 06:37 PM ----------

I was also considering turning the 5/8 down and making a 3/4 sleeve that I could weld on. Will the 3 hp have enough to run the 30 series converter?

I’m looking for any help locating a site, forum thread or experienced person to share knowledgeable information on 30 Series CVT setup and fine tuning on a 3hp engine, primarily drive ratio(s) & RPM. I would be happy to share what I learned about cheap n easy shaft adapters that will work vs the proper shaft adapter to use to get full key engagement in the PTO shaft even where I was able to finally locate a specially designed 30 series 5/8” bore clutch driver and kits designed specifically for 5/8” shaft engines.

 

[Master Hack]

I had the same problem with the same engine. This was my fix and its still working:

How to fix your shaft

If your shaft has been damaged, hacked or just isn’t as long as it should be, get your mind out of the gutter and follow along. the shaft on my lttle Briggs motor was all of the above, so l wittled out this little fix. lt looks like this on the Briggs. tomorrow l’ll make some spacers and...

www.diygokarts.com

 

[Denny]

GoKart Supply has a handy ratio calculator and a full tutorial on all CVT clutches, 20, 30, and 40 series.

 

[Barnfresh1]

GoKart Supply has a handy ratio calculator and a full tutorial on all CVT clutches, 20, 30, and 40 series.

Thanks Denny, GoKart Suppy is where my learning curve started, there and GoKartNerds which helped increase my knowledge. There’s a lot of info in the groups and forums as well as YouTube that cover CVT tuning for the 212 as well as big blocks but virtually nothing on the 3hp engines. I’ve found much of the better information is found reading though the YouTube comments however it’s time consuming. Kartcalc.net helped confirm the different numbers I was crunching for the 7” driven pulley ratios using basic online ratio calculators was correct and the notes and/or warnings it gives are in line with what I’m experiencing. Unfortunately the full app where people share results doesn’t work on my Apple devices so I’m only able to utilize the Quick Calc.

 

[Denny]

Nobody usually screws with the tiny 3hp engines.

 

[Barnfresh1]

Nobody usually screws with the tiny 3hp engines.

Uhhh yeah… precisely why I’m searching for leads on small bore resources. Thanks again

 

[bob58o]

Well I know a bit about 30 series.

If trying to get the most torque powers using the 3hp engine I suggest using a 7” driven unit and the 8T sprocket on the jackshaft if using 1/2” pitch chain. I think they sell them as 40/41/420 sprockets but there’s some differences in those chains I can’t remember.

If using 3/8” pitch chain, also find the smallest sprocket you can. Check Azusa for sprockets.

That’s if you need the torque. Also small diameter tires and a large axle sprocket will add torque to the final drive.

As for tuning the driven unit, here’s the spring and weight charts.

 

[bob58o]

Sounds like Alex’s calculator that gives warnings. Where did “itsid” go? He has it set fairly conservatively as far as warnings go.

 

[bob58o]

And your Driver unit came with that bearing instead of the bronze bushing. That’s the second time I seen that recently on here. I don’t understand why that bearing is being used now.

 

[Master Hack]

Don't under estimate the MIGHTY 3HP briggs, it does just fine in a light weight kids first kart.

 

[Barnfresh1]

And your Driver unit came with that bearing instead of the bronze bushing. That’s the second time I seen that recently on here. I don’t understand why that bearing is being used now.

They are actually two individual narrow shielded bearings. I think the original idea was to replace the thin brass bushing which people had problems with on the really low grade 3/4” China clone drivers. When the busing on genuine Comet drivers are properly maintained and lubricated they seem to work ok. I hear many people say they throw the brass bushing away and run without citing the 1” driver doesn’t come with them. I’ve been curious whether the larger diameter of the bearings doesn‘t have a similar affect as putting a sleeve over the bushing as some people say to do. I’m still struggling to wrap my head around that hack as some say the added diameter stops the the belt from dropping all the way to the lowest ratio while others claim the width limits how far the belt climbs on the pulley effectively locking out overdrive. Either way I have no issues with low gear and am running a 7” driven so no overdrive.

 

[Barnfresh1]

Well I know a bit about 30 series.

If trying to get the most torque powers using the 3hp engine I suggest using a 7” driven unit and the 8T sprocket on the jackshaft if using 1/2” pitch chain. I think they sell them as 40/41/420 sprockets but there’s some differences in those chains I can’t remember.

If using 3/8” pitch chain, also find the smallest sprocket you can. Check Azusa for sprockets.

That’s if you need the torque. Also small diameter tires and a large axle sprocket will add torque to the final drive.

As for tuning the driven unit, here’s the spring and weight charts.

I’m currently running a 7” driver and 8t on the jackshaft with 415 chain. I still need to go larger on the rear sprocket as I’m still over geared and unable to take full advantage of the tallest CVT ratio.

What I’m looking for is someone who knows what a good jackshaft to rear wheel ratio is and with what size tire so I have a baseline to calculate what size sprocket to put on my rear wheel. Comet just says “Ample”. I’m hoping to find someone knows what that would be for an ungoverned 3 horse? Also what an average top speed might be when the ratio is ample (correct) and the CVT is able to hit its highest ratio.

 

[bob58o]

The way I see it, the bearing prevents the driver unit’s movable sheave from moving as close to the stationary sheave as would be needed to “shift” into “highest gear”

If the belt doesn’t ride high on the driver unit pulley, the belt won’t try to “pull” the driven unit forward. This “belt pulling of the driven unit” is what forces the spring to compress in the driven unit allowing the driven unit’s sheaves to spread apart. This allows the belt to ride lower on the driven unit.

Measure the hole on the driver unit’s movable sheave and see if it slides over the bearing? If it doesn’t slide over the bearing, I can’t see how it will ever shift all the way into high gear.

I think it will constantly be in a “lower” gear and not shift into “highest” gear. I imagine this might cause belt slippage.

I can’t tell you the gear ratio in highest gear if the bearing prevents that from happening.

Also did you ever say what the kart was or diameter of the tires?