HELP!!! BAJA DN 150 Predator 420cc Engine Swap - Need Help and Advice

[rip_vw32]

Hello all!

Need some help here please..

The Details:

Have a Baja DN 150 frame that I've recently ripped the GY6 engine out of and swapped in a Predator 420cc engine. I have a 30 Series torque converter (TAVI 2 type), a forward/reverse gear box, and a home-made jack shaft.

I retained the original axle sprocket (31 tooth) and fabricated a drive sprocket out of the original drive sprocket off of the GY6 (16 tooth).

From the Predator to the 30 series torque convertor, with a 10 tooth driven gear, I have a chain connecting to the forward/reverse gearbox. the input of the forward/reverse gearbox is also a 10 tooth gear, so a 1:1 gear ratio so far.

The gearbox is a 1:1 forward drive, and a 1.2:1 reverse drive to the output shaft (which I have fabricated into a jack shaft).

On this jack shaft I've mounted the original 16 tooth drive gear from the GY6 and this connects to the axle sprocket (the 31 tooth)via the original Baja DN 150 double chain (I think it is a 57 link double chain).

So final drive (forward) should be 1.93:1 (31/16 right?)

The Issue:

When on jack stands everything turns perfectly. No binding, no grinding, no issues. I can shift from drive to neutral to reverse with no issues and the drive axle spins smoothly.

When on the ground however, I have to full throttle it just to get it to move a couple of inches. The belt on the torque converter slips so bad, and melts against the drive side of the torque converter.

I think that the drive ratio is off, but before I go ahead and commit to that rework, I'd like to know if there is anything I can do to the torque converter side first?

I have attached pics to help with diagnosis.

 

[JTSpeedDemon]

You need a WAAAAY lower gearing! In the region of 7/1.
The TC is fine, it just cant engage at that super high gearing. Fix the gearing!
It's not just off, it's completely wrong.

 

[bthompson224]

Geared way too high.

 

[rip_vw32]

You need a WAAAAY lower gearing! In the region of 7/1.
The TC is fine, it just cant engage at that super high gearing. Fix the gearing!
It's not just off, it's completely wrong.

Cool!! I thought so, and I appreciate the answer - so now the question is where???
Where do I put a bigger gear?
On the jack shaft?
The input side of the gearbox?
On the drive axle?

I am lost on this one guys, so appreciate the input... Also, recommended gear for the specific placement?

 

[JTSpeedDemon]

I would put a much bigger sprocket on the axle.

 

[bthompson224]

Not sure you can just do that, big friggin sprocket might not clear the ground. You may have to go both lower on the jackshaft and bigger on the axle, like a 12t to 80t.

 

[rip_vw32]

I would put a much bigger sprocket on the axle.

I can do the math, but like i said I am new/lost on this..

So, if I understand this, I can go to a 112 tooth axle sprocket (keeping the existing 16 tooth drive sprocket) OR a 70 tooth axle sprocket and a 10 tooth drive sprocket on the jack shaft, right?

Does that sound right?

 

[bthompson224]

Yes. As long as you are between 6 or 7 to 1 you'll be fine. Again, that sprocket has to be less in diameter than your tires. My 80t is about 12 inches, I would guess. How much less depends on how close to the center the sprocket sits.

 

[rip_vw32]

Yes. As long as you are between 6 or 7 to 1 you'll be fine. Again, that sprocket has to be less in diameter than your tires. My 80t is about 12 inches, I would guess. How much less depends on how close to the center the sprocket sits.

Really appreciate the input... now I just need to find a double row 112 tooth sprocket OR buy a new single row set...

Again - thank you very much!

 

[mckutzy]

I see you have some relatively big chain...And double at that....Why double sprockets and what size is that?

I can see you needing to replace all big stuff that with a common size, like 40/41 even....

With that, ratio's can be better tailored to the needs, and itll fit. That big stuff is just that... big, so the required sprockets might not even fit or have no ground clearance...

Here is a calc for the jackshaft ratio....

https://affordablegokarts.com/pages/gear-ratio-calculator

 

[rip_vw32]

I see you have some relatively big chain...And double at that....Why double sprockets and what size is that?

I can see you needing to replace all big stuff that with a common size, like 40/41 even....

With that, ratio's can be better tailored to the needs, and itll fit. That big stuff is just that... big, so the required sprockets might not even fit or have no ground clearance...

Here is a calc for the jackshaft ratio....

https://affordablegokarts.com/pages/gear-ratio-calculator

So the drive sprocket and the axle sprocket are hold-overs from the original GY6 that was in the DN 150 to begin with. I wanted to keep the thing as original as possible on the drive side, figuring I wouldn't have gear ratio issues - and I was wrong.

I can't find the specs on the axle shaft size, so I have no idea what driven gear I need, and I'll need to replace the drive (16 tooth) sprocket with a 10 tooth 3/4 inch sprocket, and between a 60 and 70 tooth axle sprocket to match.

I REALLY wish that there was a local go cart place here in Denver to buy this stuff at....

 

[JTSpeedDemon]

Well, the reason why the original gearing wouldn't work, is because GY6s have quite a bit of internal gear reduction.
As for buying sprockets, just do the usual bmikarts.com, ombwarehouse.com, or gopowersports.com

 

[mckutzy]

Your going to have to measure the sprocket tooth to tooth to confirm what exactly type of chain you have...

As far as I can see... its a #530 type chain..... which is a motorcycle rated type chain....
This limits you for what you can use, as this is used with a machine that has a transmission.
This allows it to be used with a broad range of ratios... in your case the CVT only goes so far...
So this limits you to what you can use.... so in our case(here in DIYGK and other gokart/buggies) we typically have to use the #40/41 and #35 to get better ratios with out sacrificing space....
A #530, 72t is 14.32"OD, A #35, 72t 8.810"OD for example...

So that basically why we use industrial chain and sprockets for our application, also as its more common and less specialized

 

[rip_vw32]

Thanks everyone - And ya, started thinking about the planetary setup in the GY6 after the discussion started here... so, here is what I am going to do, let me know if this is advisable:

Replace the 16 tooth double sprocket with a 10 tooth 3/4" single row #40/41 sprocket.
Replace the 31 tooth double axle sprocket with a 60 tooth single row #40/41 sprocket.

i just need to figure out what axle sprocket 'size' I need.

 

[mckutzy]

Here is a chart for the sprockets sizes...
https://www.ablproducts.com/40-41-chain-sprocket.html

If You want to keep the reverse box you have, youll need to find a sprocket that will fit in the space available between the shaft boss of the rev/box to have enough clearance...
Equally speaking youll need to measure out for space to see what you can accommodate as far as the jackshaft sprockets...

Dont forget to measure the ground clearance with regards to the rear axle sprocket on the ground...

 

[JTSpeedDemon]

What's the rear tire diameter?

 

[rip_vw32]

What's the rear tire diameter?

Sedona Mud Rebel 25x11-10

 

[cleatusj]

I would put as large of a sprocket, on the input to trans as possible, to help reduce the size needed on axle.

 

[JTSpeedDemon]

I don't think sprocket clearance will be a problem with 25" tires!
Yeah, get a BIG FAT DADDY sprocket on there!

 

[mckutzy]

What is the actual measured OD size from the ground... sidewall are misleading...