Help with 4stroke engine coupled with a 2002 Ezgo Dana Spicer transaxle

[slonomo]

Those "torque-a-verter" type cvt transmissions are not meant for a heavy vehicle like the golf cart, so I wouldn't be surprised if the belt was slipping. Golf carts use a 1" or 1 3/16" belt, as opposed to the 3/4" sized go kart belt. The cvt and belt would be my first suspected place to look for slippage. Everything else is gears, and you would hear gear type noises. You could roll the cart on the garage floor and verify that it spins the gears on the jack shaft, that would eliminate the golf cart transaxle.

[CCGC2004]

Thanks for the reply. Seeing as the gy6 with the same kind of 1/2" v-belt in the original gear ratio set up would get the cart plus the weight of me and my son moving at 25mph, I think it has the power but I am having trouble getting that power to the transaxle. I just tested again...the CVT output is turning the jackshaft smoothly and the cart is quicker to initially get the gears in the transaxle moving (can feel that initial take-off grab in forward and reverse) but then it does not want to get up to speed and keep moving as more throttle is given. Still no grinding noise which is good. I did just notice after a closer look that the new 3 1/2" pulley seems to be about 1/16th" more narrow than the original 3 1/2" pulley attached to the transaxle input. The top of the belt is not getting down into the pulley all the way (between 1/16th and 1/8th" showing). Could this be part of the cause of the slip? Also, what you said about not habing a beefier belt makes sense to me for the lack of power transfer to low end torque (even with the original v-belt set up that was geared for speed vs torque). Maybe this is the main problem in not getting low end torque. I would like to try a more substantial belt from the jack shaft to the transaxle to test this theory but I cannot find pulleys for that type of belt that will fit onto the 3/4" jackshaft and the 19 spline transaxle input shaft. The outer diameter of the current v-belt is 26" based on the current pulley size and 7 1/2" distance center to center between the jackshaft and transaxle input shaft. Can you recommend any...know where I can find them? Thanks again for the advice and assistance!!

[sho305]

That belt will have to be fairly tight to not slip. You also have to take into account the ratio of the rearend. I would try reducing your overall ratio by say 25% that would give a 20mph speed and that much more torque, I'm not sure if that is what you did; where your final ratio is now. I have a friend with a GY6 yard cart it runs near 30mph I'm not sure on engine size possibly 150cc, land master 202 or yardsport ys200. Figure a stock cart will run about 20mph with a 9 hp engine and has plenty of power to go up hills and take off etc. A V belt can not go all the way down into the pulley or it will slip for sure if it hits the bottom of the groove. A V belt, not a CVT belt. I assume the CVT is what came with the engine and is correct.

As far as swapping the rear front to back it might work but then you are running in reverse which can have a different ratio. The rear would have to be at a similar angle to get similar oiling inside. You can rotate the axles some on some of them, again need to make sure it is oiling inside and you didn't change the angle of the case too much. If you have a cvt on the engine you could also use a chain drive for the rest. A belt is good to reduce shock load to the rear but a cvt should not have any shock load really.

A BMS Avenger probably has a similar engine.

[slonomo]

Originally Posted by sho305

I would try reducing your overall ratio by say 25% that would give a 20mph speed and that much more torque, I'm not sure if that is what you did; where your final ratio is now.

Earlier in the thread I suggested that, but the OP said he couldn't fit the gears he wanted. I still think it's a gearing issue. At this point we still don't know his overall gear ratio/final drive ratio at the tires. That little engine doesn't have the low end power to drive tall gear ratios. If the jackshaft gears were a 1:1 so that they transmit the engine torque straight to the cvt, then you should have a similar power setup compared to stock. The only weak link at that point is the cvt belt being small and the clutch spring pressure being different than a golf cart, not to mention shift profile of the clutches.

The other point is power. A 170cc go kart engine vs a 295cc twin cylinder golf cart engine? Two drastically different powerplants. Not sure how anyone could expect the two to be similar. I know the 295 Robin engine is only 9hp, but it's made for that cart and has the proper cvt setup to push a 700 lb machine with 800 lbs of cargo. This go kart engine and cvt was made for a machine half the weight to propel a 150 lb kid. I'm just not seeing it.

[CCGC2004]

Thanks guys. The CVT has the correct belt, I dropped the variator weights to 10g sliders and upgraded the driven clutch to yellow 1500rpm main and small springs. Watching the CVT function through steady increase of rpm, it does not appear to be the issue. Under load it does not appear to slip. Per Slonomo's previous help, I was thinking switching the jackshaft v-belt out for a more substantial belt/pulley set up or even switch out for a second chain drive but I can't seem to find the sizes I would need to pull it off. I changed the gy6 output sprocket to 19 tooth (smallest 19 spline sprocket I could find to fit the 428 chain), which drives the 24 tooth sprocket (largest I can fit) on the jackshaft. On the opposite end of the jackshaft I have a 3.5" pulley driving another 3.5" on the transaxle input shaft with an A24 (1/2" x 26") v-belt. The Dana Spicer transaxle has a 12.44:1 ratio. The rims/tires are 23x10.50-12. So, with all of that is it possible to determine my final gear ratio??

[slonomo]

For the calculation, you would also need the diameter of the cvt pulleys. I'm def not a mathematician, so I'll leave the math to someone else lol.

[CCGC2004]

The CVT variator is 108 mm OD
and driven clutch pulley is 135mm OD which I think are both standard for 150-175cc.

[CCGC2004]

Any math/gear ratio gurus out there that could lend their talents?

[sho305]

You just multiply the ratios together, divide each drive set to get the ratio for it. I was talking about after the GY6 I see you have a chain and a belt drive to the rear, that belt may be slipping. I have no idea what ratio your electric rear is, stock gas carts run around 12-13:1 rear with a cvt that does .9 overdrive, so that comes out to around 10 or 11:1 final ratio engine to axle. Or if its a gas rear you can find that info here easily. I assume the GY6 and its cvt are working correctly and I would mess with it last. The GY6 yard carts run fine up to 30mph even with 600lb of people and cargo in the back. It might be faster than my stock G9 with 22s was, with modded clutches and no governor that also went 30mph. That is why I don't think its the GY6 at fault here but I could be wrong.

My guess is figure the ratio of your rear, the ratio of both chain and belt drives, multiply them all together and should be around 10-12 to be comparable to a golf cart that runs 20mph on 18 tire and 30 on 22 tires. That just a guess. So if your rear is say 14:1 and your chain and belt is .9 and 1.0, the 1.0 does not change it so toss that, 14 x 0.9 = 12.6 ratio from GY6 to axles. The circumference (diameter x pi) of the pulleys or sprockets (or teeth numbers) will show the ratio. If the drive is larger than driven its gearing up and will be 0.x less than 1.0, if the drive is smaller its reducing and will be high ratio more than 1.0. So a 40 teeth drive sprocket and a 35 driven is .875 (35/40=0.875:1 ratio, so use 0.875 for the ratio of this drive to multiply with the other drives). If the sprockets were reversed its reducing the ratio will be higher than one so 40/35 = 1.14 or 1.14:1 ratio.

I don't know if the GY6 cvt overdrives or not. If the belt falls into the secondary deeper than the top of primary at full shift it should be overdriving. Most only OD a little for a .9 final ratio, however the GY6 may not or not need to because it will rev much higher than a lawn or golf cart engine does, so you have more rpm you don't need as much gearing as a slower engine would to get same speeds. They must run near 6K rpm or something while stock lawn is 3600 and no governor is 4300 or so. The max rpm is an important factor in gearing so your GY6 would be different ratio than a slower running 9hp lawn engine, it would have a higher ratio.

I think that is all right, anyone correct me if wrong.

[slonomo]

Most cvt vehicles drivelines will have a parasitic loss in power of around 20% give or take. I'm thinking this one, with all of it's different gears and chains etc will likely have more loss than standard. If you said 30% loss, that 9hp just changed to 6hp. Not accurate, I know, but it's probably in the neighborhood. Just saying you might want to take that into account with how much power you will actually see at the rear wheels. It's not going to have very much power, so just plan for that with how you use the machine.