Need help deciding on sprocket sizes

[raposak]

no way to do it without the jackshaft. I'm using #50 chain which is much beefier than the standard gokart chain.

 

[r97]

All I'm saying is the jack shaft should have a 1:1 on the input side, then all of the reduction should be on the output (if you are using the jack shaft to relocate the chain, fine, just no primary reduction).
#50 chain may be much stronger than standard go kart chain, but your not using a standard go kart engine either. Plus in first gear you already have a reduction of about 6:1 before it gets to the counter sprocket.

So 46ft/lbs from engine*6*1.5=414ft/lbs into the jack shaft. Your 15t js output sprocket has a 1.5" pitch radius, so that works out to 3312lbs of chain tension. #50 chain has a working load of 1400lbs. Without the reduction on the jack shaft, a 16t sprocket gives a 2070lb chain tension.

I will also mention that the mini buggy and motorcycle crowd have found #50 industrial chain too weak. You should be looking into #530 motorcycle chain which has the same dimensions (fits #50 sprockets) but is much better suited for this application.

Now all of that said, one thing that has worked has been to use a jack-shaft (with primary reduction), but then they use double row #50 chain (expensive, heavy, less efficient).

Why exactly do you want a jack shaft anyway? Sprocket clearance? Chain relocation?

Hope that helps!

 

[raposak]

thanks for the info. i'm running a js because the motor will be mounted above the swing arm. The js will be on the same plane as the swing arm pivot points.

 

[r97]

Yeah that's fine, just really try to avoid a reduction on the input if you can. Good luck, can't wait to see it finished!

 

[raposak]

Well the 70T axle sprocket is a no-go. The thing is a massive hunk of steel that's WAY too big. I went from originally going with 27" rear tires to 24" tires. Now I have to start over......... Any more help is appreciated.

 

[r97]

Well, as I mentioned you can run a reduction on the primary reduction side of the js, but definitely look into 50-2 chain. You can try standard #530 if you want, it may very well work, but I think the better bet is on the #50-2. Good luck, hope that helps. Can you try and return that sprocket? probably wasn't cheap.

I'm guessing the sprocket is hitting the frame or killing ground clearance right? If not and your concerned about weight, add some big holes in it!

 

[raposak]

Well here are some pics for reference. The 3rd pick is a 25" tire with the new spocket with the factory bike sprocket for comparison. Tell me what you think? Think its too big?

 

[r97]

That is a pretty big sprocket, I guess you should look into other options, that is unless your fine with that sprocket size. One thing you could do is try and place the sprocket as close the one tire as possible, this way the wheel will ride over rocks that would normally just hit the sprocket. If you do that make sure you have good support from the bearings, the chain will be trying very hard to bend the axle.

The best thing would be a chain running to a heavy duty gear case on the axle. Would get reduction just like a jack shaft, but the secondary would be big spur ol' gears in an oil bath; but I kinda doubt your not terribly interested in that Idea if you can avoid it correct? (lots more un-sprung weight...)

Again, look in to the double chain, a few people on minibuggy.net have used it on their builds to solve the same problem you have.

 

[raposak]

Well here are the gears I currently have to work with.

Engine/Jackshaft
12
13
13
15
16
27

Rear Axle
28
43
45
72

Like I said, the 72 is entirely too big. I don't mind buying another sprocket for the rear axle, but it has got to be smaller than the 72 I have. With the above sprockets, what would be a good combo to go with?

 

[anderkart]

Speed is good, but I also need stump pulling torque. I want to be able lug the engine up a hill without feathering the clutch.

Well the 70T axle sprocket is a no-go. The thing is a massive hunk of steel that's WAY too big. I went from originally going with 27" rear tires to 24" tires. Now I have to start over......... Any more help is appreciated.

Well here are the gears I currently have to work with.

Engine/Jackshaft
12
13
13
15
16
27

Rear Axle
28
43
45
72

Like I said, the 72 is entirely too big. I don't mind buying another sprocket for the rear axle, but it has got to be smaller than the 72 I have. With the above sprockets, what would be a good combo to go with?

I re-calculated using:

24" tires
45 tooth rear axle sprocket
12-T countershaft (transmission output)
27-T jackshaft in
12-T jackshaft out

At 14,500 rpm, this gearing calculated out to:
21-mph in 1st gear
29-mph in 2nd
38 in 3rd
44 in 4th
51 in 5th
and 57-mph in 6th.



I noticed r97 suggested using the same tooth count for your countershaft and jackshaft-in. I cant deny or confirm this as a fact, but with all the info you supplied this seemed to be the only gearing to achieve your goal.

 

[r97]

I noticed r97 suggested using the same tooth count for your countershaft and jackshaft-in. I cant deny or confirm this as a fact, but with all the info you supplied this seemed to be the only gearing to achieve your goal.

He could very well be fine with a reduction from counter-shaft to jack shaft, but then again maybe not. He is welcome to try it first (he already has the materials so why not right?) but I'm just passing on the information that the secondary chain in applications very similar to this has been proven to fail more often than it should.

With the above ratio the secondary chain needs to put up with the same force the primary chain does, multiplied by 2.25. I will also mention that keeping the chain cool, and increasing the size of the sprockets (not changing ratio) will also prevent failure.

 

[raposak]

Appreciate all the suggestions. I will give it a try and see what happens. Worse case scenario is I blow chains some gears and possibly a jack shaft lol.