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Discussion Starter #1
Hello everyone. I recently picked up this bike and the engine has a little knock in it. Thinking about getting the tbolt 88 kit with carb and cam. While I'm at it I'm considering replacing the crank (stock) and upgrading the trans.

I've read that guys don't like the ratios on the ahp 4 speed kit.

I will be using this bike as a kids bike for a 10 year old as well as something for me to mess around on. We have a little track in our yard that gets ridden daily by me and my friends as well as my kids. We also go to the desert a lot but I'm not too concerned about top speed.

So... can anyone tell me what parts I would need to buy to do the XL/SL swap or another swap that provides close ratios?
 

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I run the AHP in my 50, I like it a lot and have had 0 issues with it. If its a mess around bike and for a 10 year old then who cares if the ratios are off a little bit.
 

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I run the AHP in my 50, I like it a lot and have had 0 issues with it. If its a mess around bike and for a 10 year old then who cares if the ratios are off a little bit.
Well I'll be using it too and why bother swapping it if the ratios don't improve. How do you like the ratios on your ahp kit?
 

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I like them. I considered that Takegawa if I remember correctly. the reason I went AHP is that had a slightly taller 4th and since mine is on the street, that is what I wanted. It has a normal 1 down 3 up shift pattern compared to an early honda 4 speed trans and I also wanted new parts. With the 4 speed you can alter your final drive more and have more usable gears compared to the 3 speed that is stock. you already have a different primary drive internally being a 70 compared to a 50. I did the manual clutch which gave me the primary drive of the 70. In a full tuck I can hit 75 mph. never mind what the engine side is :). You mentioned that you want to improve the ratios. That is very subjective, only you know what that means. If you want closer ratios, you can change your final drive and pick any 4 speed and get another usable gear.
 

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Discussion Starter #5
I'm looking for close ratio. I can find bran new old stock xl70 stuff, just not sure what all I need to complete the swap. I also can't find info on the ratios with the XL or atc or trx transmissions. If anyone has this info please help. Thank you
 

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I would think when you go from a xr70 3speed, to a 4speed, the ratios get a LOT closer with the Xtra gear.

If you'll be keeping the semiauto clutch, you'll want a 4up or 4down. 1d 3up is said to be hard to find neutral with the semiauto.

If you need closer ratios than the Honda or ahp, I think Takegawa makes one, for about 3x the money.
 

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Discussion Starter #8
I would think when you go from a xr70 3speed, to a 4speed, the ratios get a LOT closer with the Xtra gear.

If you'll be keeping the semiauto clutch, you'll want a 4up or 4down. 1d 3up is said to be hard to find neutral with the semiauto.

If you need closer ratios than the Honda or ahp, I think Takegawa makes one, for about 3x the money.
See I read another thread that was saying the ahp had a granny first gear, huge jump to 2nd gear, 3rd gear was good and 4th was freeway gear, I'd prefer close ratio and change rear sprocket as needed.

I think it was that same thread that was saying the Honda 4 speeds were closer then the ahp but no specs and not sure what to buy or what's compatible.
 

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10 minutes google

stockAHPATC70tak3sptak4spkit3spCT70hk1XL/SL70
13.2723.1823.2722.6152.6152.6152.6922.833
21.6671.7061.9381.6671.8231.6671.8231.875
31.1901.2381.3501.2851.3501.2851.3001.300
4-0.9171.043-1.090-0.9580.958
$0$150$110*$240$400???

You decide

*dratv sold the ATC70(82-85) trans ratios as a kit for $110(trans $60, shift drum/forks $50) but has them listed as out of stock
 

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You can find used atc70/trx70 transmissions on eBay for $60-120. Then add about $80 for new shift forks and shift fork pins. Genuine Honda 4speed trans, 4up or down, for less than $200.

If you plan to keep the semi-auto clutch, I think all that you need for the swap is the transmission with shift drum. And make sure to use the correct pinion gear on the kick shaft. Your XR70 should have the correct pinion for the ATC/TRX/AHP transmissions. If you use a H trans, you'd need a different kick shaft and pinion.
 

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Well that sucks on my mobile the table isn't there. View on PC to see ratio table.

I don't know the quality but I believe the shift drum and fork kit is available from dratv still for $50. Could use that and pick up a used atc70 gearset
 

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I can see it.


10 minutes google
stockAHPATC70tak3sptak4spkit3spCT70hk1XL/SL70
13.2723.1823.2722.6152.6152.6152.6922.833
21.6671.7061.9381.6671.8231.6671.8231.875
31.1901.2381.3501.2851.3501.2851.3001.300
4-0.9171.043-1.090-0.9580.958
$0$150$110*$240$400???


You decide​





Looks like DRATV has them in 4d or 1d3up.
I think it's a lifan part.
SHIFT_PATTERN CONVERSION_KIT FOR_HONDA_OR CLONE_4SPEED TRANNY'S
 

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On my phone I just see a cludge of numbers. Fine on my PC though.

Looking for a source of the ATC70 ratio trans.

The question here is can a CT70 and ATC70 trans be mixed together to make

1 - 2.692 CT70
2 - 1.823 CT70
3 - 1.350 ATC70
4 - 1.043 ATC70

Then there are the primary drive gear ratio options to move the whole lot up and down
 

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Discussion Starter #14
Thanks guys, this is what I was trying to find out. It would be nice to know if you can mix parts from the different machines to change ratios but unless someone has those parts in hand I don't see a way to figure it out.
 

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I'd imagine that you could. You'd just swap both gears (2nd, 3rd, etc,) from both shafts together. But the big brains at Honda put these combos together. I'm curious what your perfect setup would be? Can you tell us your perfect transmission, ratios...1st thru 4th?
 

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Discussion Starter #16
I'd imagine that you could. You'd just swap both gears (2nd, 3rd, etc,) from both shafts together. But the big brains at Honda put these combos together. I'm curious what your perfect setup would be? Can you tell us your perfect transmission, ratios...1st thru 4th?
I don't know what the perfect ratios would be. I just know the stock gears aren't right for a mini track. The jump from first to second is way too tall. First gear is fine but as soon as you go to second there's just no power at all, can't even get into third because 2nd is so tall and underpowered.

If I change sprockets first gear becomes so low that it's not useable (for my application).

My dad still has my trx70 from when I was a kid and I have a few friends with atc 70's. I guess riding those could be helpful in figuring out which gears would be best.

Has anyone else done the swap with Honda parts?
 
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