Chinese Honda ST clone

[ricardoguitars]

Hello everyone :hi:

My wife is learning to ride, she is now practicing on a scooter but she doesn't like the sitting position of the scooter, she is on the small side (don't tell her I said that! :hehe:), a full size bike is too tall for her to start on and feel confident being her a beginner, so I thought about the Honda ST clone, she likes it, so we will check one this weekend at the local dealer. One thing that worries me is that the one available around here is a 90cc, that's just fine for around town, but not sure about hill climbing, I live up a mountain so that is an issue, it won't be nice for a newbie rider having a mob of angry cagers behind her honking and overtaking dangerously because she is going too slow uphill :ohno:. The question is, I have seen ST clones on a 125cc configuration, the scooter is 125cc and do just fine doing those same hills, so is it possible to buy a 125cc jug and piston (BBK?) and putting it on the 90cc engine? :hmm:

This is the bike:

http://bisqa.com/sitios/MOT17V3/images/gallery/REX%20Path.png

[ricardoguitars]

I just found those bikes where called ST, DAX and Trail, depending on your geography.

[Bruce's]

That is a ct70 clone not a st90 clone ,st90's are a little larger bike ,and they have spoke wheels and were only available for about 3 years or so ,at least in North America .Anyways ,the bike you are looking at will have a general pit bike engine in it ,yes you can make it a 125 ,bit it will take much more than a jug and piston ,they sell those bikes with bigger engines in them ,or you would be better off swapping an entire larger engine in rather than dealing with the issues making the engine larger .

[ricardoguitars]

That is a ct70 clone not a st90 clone ,st90's are a little larger bike ,and they have spoke wheels and were only available for about 3 years or so ,at least in North America .Anyways ,the bike you are looking at will have a general pit bike engine in it ,yes you can make it a 125 ,bit it will take much more than a jug and piston ,they sell those bikes with bigger engines in them ,or you would be better off swapping an entire larger engine in rather than dealing with the issues making the engine larger .

Thanks Bruce :tup: I don't think one can source a 125cc engine here, I have only seen this bike as a 90cc here in Costa Rica, so my options are limited to upgrade the stock engine :shrug: I can buy the needed parts from the US or pretty much anywhere around the world, but exporting a complete engine would be more expensive than the whole bike :doh:

Do you know what is needed to do the upgrade on the stock engine? I would like to know that before pulling the trigger on the bike.

:thanks:

[Bruce's]

I wouldn't bother doing it ,but you will need a new crank ,the cases will need to be machined ,chances are the bushings in the cases will need to be replaced with bearings ,the cylinder ,piston ,bigger valves or a new head ,depending on who the actual manufacturer is of the original engine and how cheap it was built ,starter shafts and gears are stronger as well ,it would be fun to do but the reality is it doesn't make financial sense when you can buy a properly built engine complete for less than the price of the parts .I guess a carb,and exhaust would have to be added as well .

[ricardoguitars]

I wouldn't bother doing it ,but you will need a new crank ,the cases will need to be machined ,chances are the bushings in the cases will need to be replaced with bearings ,the cylinder ,piston ,bigger valves or a new head ,depending on who the actual manufacturer is of the original engine and how cheap it was built ,starter shafts and gears are stronger as well ,it would be fun to do but the reality is it doesn't make financial sense when you can buy a properly built engine complete for less than the price of the parts .I guess a carb,and exhaust would have to be added as well .

Seems like a lot of work, not worth it. I have not driven a shifting bike smaller than 150cc, the smallest bike I have driven is my 125cc GY6 scooter, do you know how big of a difference the 150cc is from a 90cc speed wise and climbing hills? I didn't notice a huge difference going from a 150cc CB clone to a 250cc dual sport, both peak at 90km/h, the dual sport has taller gears, so it performs a bit better climbing hills as expected, but not a huge difference. :hmm:

[Adjuster]

Will no one ship a 125 engine to you in Costa Rica? They are all over Ebay.


/

[ricardoguitars]

Will no one ship a 125 engine to you in Costa Rica? They are all over Ebay.


/

The problem is not logistics, the problem is taxes and freight charges :doh:

[Weldangrind]

IIRC, the 90 shares the same stroke as the 110, so you could (theoretically) swap a 110 jug and piston onto the 90, perhaps without needing to hog out the case. it wouldn't gain you much, but 20cc's would help. As Bruce pointed out, you'll need to rejet and you'll likely want a free-flowing exhaust.

[Bruce's]

The actual Honda 90 cc engine is that way Weld ,but the one pictured is a z50-ct70 style pit bike engine ,as far as I know nobody is copying the Honda 90-110-125 (125 m three wheeler )units which is a little different with the ignition on the cam in the head ,and the lower mounting point is in a slightly different place .To get a 50-70 to 90 cc ,is just a jug and piston or a bore job netting 88 cc which is cheap and easy ,after that you start into cranks etc to get larger ,then you have to beef up everything else as you are now stressing the engine well above its usual power .I wouldn't bother building one myself when I can buy a good new one for $20-$40 more than a clone 70 .

[Weldangrind]

This is an interesting discussion, Bruce. I also understand that horizontal clone engines are based on the Z50 case, typically topping out at 125 (exceptions are the high-strung Piranhas, etc that are 140, 150 and beyond). The bore and stroke relationships as I understand them are as follows:
- 50 and 70 share a crankshaft but have different bores
- 70 and 90 share a bore but have different strokes
- 90 and 110 share a crankshaft but have different bores
- 110 and 125 share a bore but have different strokes
I can't recall where I learned all that, but it was most likely Dr. ATV or Scrappy Dog. If that info is correct, then a 90 could be bored to a 110 with just a cylinder and piston. I have no way of proving or disproving my statements, although I might have a Baja 90 crank laying around.

[Bruce's]

I am not an expert on them other than anything over 88 cc becomes a money pit ,and just not worth it to build one yourself when you can buy one ready to go for less .I originally thought you were talking trail 90 -110 engines ,which are a totally different animal .From what I do remember in pit bike engines ,50-70have a different bore ,installing an 88 cc kit is also a bore ,110 gets into a crank ,and after that I just do not remember at all ,I have found it's not worth doing much internal repair work on anything 110 cc or bigger ,just get another engine ,they are usually highly stresssed and generally not worth getting into .I think dr atv would be where you can easily find out the combos for the different displacements .

[dirtbkr188]

Typically, a 90cc (really 86cc) Chinese engine will have a 47mm bore and a 49.5mm stroke, and the cylinder is usually 69mm tall. Using a 54mm big bore kit will yield a final output of 114cc (really 113cc) and you shouldn't have to bore the cases, most of the Chinese engines will accept the 54mm spigot. I believe it is a 13mm wrist pin, as well.

Click here (http://www.tbparts.com/product/tb-114cc-high-compression-bore-kit-86cc-107cc-engines/) to see the TBParts.com kit

[ricardoguitars]

The engine model is 1P47FMF according to the dealer, that might help solve the mystery :D

[Bruce's]

This is more along the lines of the kits I was talking about for a 110 conversion on a crf type engine .I don't know enough of the ins and outs of the clone internals ,but dirtbkr's post shows it might be a doable deal if you are starting from a clone ,I have several blown up clones and originals here in all sizes ,I might pull a few top ends off and try mixing and matching different barrels to see if everything does work as drtbkrs post shows .

[pete]

The chinese copys are a copy of the Honda 70..
Honda 90 & 110 motors are the same concept but
bigger/heavyer built..
Honda wern't prepaird to stretch the 70 out to 90 then 110
they built a bigger more robust motor..

I have a CT110 and a chinese 110 copy... you can see the physical size diffrents..
the Honda 110 is a bigger motor size wise...


..

[dirtbkr188]

I might pull a few top ends off and try mixing and matching different barrels to see if everything does work...
Bruce,
One thing to keep in mind is that the engine stud spacing may vary slightly between Chinese engines and also may be different than the Honda spacing. That slight variation can result in mismatched parts bolted together without any dowel pins used at all to keep the top end aligned on the cases. I've seen it firsthand.

[ricardoguitars]

This is more along the lines of the kits I was talking about for a 110 conversion on a crf type engine .I don't know enough of the ins and outs of the clone internals ,but dirtbkr's post shows it might be a doable deal if you are starting from a clone ,I have several blown up clones and originals here in all sizes ,I might pull a few top ends off and try mixing and matching different barrels to see if everything does work as drtbkrs post shows .

That would be awesome! :thanks:

[Weldangrind]

Since we all agree that the China pit bike engines are copied from the Honda 50-70 case, We can talk apples to apples. I'm saying that I think the 90 and the 110 China pit bike engine share a crank but have different bores. If that's true (and I'm not sure), then this kit would be a bolt-on deal: http://www.ebay.com/itm/52mm-Cylinder-Piston-Pin-Ring-Gasket-Kit-for-110cc-ATVs-Dirt-Bikes-Go-Karts-/192107121337?epid=0&hash=item2cba7a0ab9:g:kwUAAOSwr~lYqmHJ&vxp=mtr
The price is certainly right.


https://i.ebayimg.com/images/g/kwUAAOSwr~lYqmHJ/s-l400.jpg

[Bruce's]

I think you are right Weld ,it seems the Chinese clones have the ability ,yet the Honda engines do not have the crank or the block machined to work with that kit .Of course ,it just opens up a can of worms ,does the head work well with the bigger cylinder,need a bigger carb with it ? ,exhaust ?

[ricardoguitars]

Since we all agree that the China pit bike engines are copied from the Honda 50-70 case, We can talk apples to apples. I'm saying that I think the 90 and the 110 China pit bike engine share a crank but have different bores. If that's true (and I'm not sure), then this kit would be a bolt-on deal: http://www.ebay.com/itm/52mm-Cylinder-Piston-Pin-Ring-Gasket-Kit-for-110cc-ATVs-Dirt-Bikes-Go-Karts-/192107121337?epid=0&hash=item2cba7a0ab9:g:kwUAAOSwr~lYqmHJ&vxp=mtr
The price is certainly right.


https://i.ebayimg.com/images/g/kwUAAOSwr~lYqmHJ/s-l400.jpg

I wouldn't mind paying 30 bucks for 20cc more :clap:

[Mudflap]

On Lifan engines the 125/140/150 has a different head with larger valves than the 110 and smaller engines. Have no idea about other brands.

[dirtbkr188]

Just an FYI, a 52mm big bore kit does bolt right up to a Honda lower end, no case boring required. You do have to case bore to go up to a 54mm big bore kit on a Honda, but shouldn't have to on a Chinese lower end, the case bore is big enough for the 54mm spigot.

I apologize if I've created any confusion...

[Weldangrind]

I wouldn't mind paying 30 bucks for 20cc more :clap:

It's a gamble, but not much of one.

[Weldangrind]

I think you are right Weld ,it seems the Chinese clones have the ability ,yet the Honda engines do not have the crank or the block machined to work with that kit .Of course ,it just opens up a can of worms ,does the head work well with the bigger cylinder,need a bigger carb with it ? ,exhaust ?

I've heard the same thing as Mudflap, which is that everything smaller than 110 (in the Chinese clone world) shares the same head. A jump from 90 to 110 would certainly require bigger jets, but I suspect that's it.

[pete]

I think you are right Weld ,it seems the Chinese clones have the ability ,yet the Honda engines do not have the crank or the block machined to work with that kit .Of course ,it just opens up a can of worms ,does the head work well with the bigger cylinder,need a bigger carb with it ? ,exhaust ?


the head will work better with a bigger bore as the side of the valves
closest to the cylinder wall have better flow because of more space..
providing you havn't gone that big that to valves are to small to fill
the cylinder....


...

[Weldangrind]

I agree with your logic, Pete. Unshrouding the valves will promote better flow.

[ricardoguitars]

I picked it up on Saturday, the engine is the one with the semi-auto gearbox, no clutch, you just push down the gear lever to go from neutral to 4th gear, and pull up to go from 4th gear to neutral, it is a bit weird, you have to be careful when shifting to avoid a willie when upshifting or hard braking when downshifting.

Here is a video of the first ride, I figured out the reverse gear order when I saw the gear order label on the side of the bike, lol. It runs faster than I thought it would, the chinometer says 70km/h, but I have to GPS test it to get the accurate measurement.

https://www.youtube.com/watch?v=ZjimzpwiFnQ