What's the difference?

I weld mounts directly to my frames. Just like with a real motorcycle. Makes it easy to align and pull and place motors when working on them. An no vibrations from squishy mounts. Lol
Or make your own mounts like i did for my bike...it doesn't budge...lol...DAMIEN
 

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As far as I know there are really 3 main engine sizes with these 'China Doll' engines and these are determined the diameter of the piston.

* 49cc - 40mm piston
* 70cc - 47mm piston
* 100cc - 50mm piston

Even tho some suppliers refer to them as 80cc, if you actually use the 47mm bore and the 40mm (some are 39.5mm) stroke measurements to do the calculations, the number will be closest to 70cc. There are two types in the 47mm piston group - high pin and low pin and as the name states, the difference is determined by the location of the pin on the piston body and con-rod lengths. The rods and pistons of the two ARE NOT interchangeable - if you mix the components, you will most likely smack the piston into you head - you have been warned ! Lol so make sure you double check with the supplier when buying replacement cylinders and/or pistons and state which version you have 'high' version piston with the 40mm rod OR the 'low' version with the 38mm rod.

The main stud locations are the same for the 40mm & 47mm piston hence you can use either jugs on the same crankcase, but due to the larger 50mm piston on the larger version, the stud locations are wider apart and hence are not interchangeable with the other two sizes.

Hope that helps.
 
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As far as I know there are really 3 main engine sizes with these 'China Doll' engines and these are determined the diameter of the piston.

* 49cc - 40mm piston
* 70cc - 47mm piston
* 100cc - 50mm piston

Even tho some suppliers refer to them as 80cc, if you actually use the 47mm bore and the 40mm (some are 39.5mm) stroke measurements to do the calculations, the number will be closest to 70cc. There are two types in the 47mm piston group - high pin and low pin and as the name states, the difference is determined by the location of the pin on the piston body and con-rod lengths. The rods and pistons of the two ARE NOT interchangeable - if you mix the components, you will most likely smack the piston into you head - you have been warned ! Lol so make sure you double check with the supplier when buying replacement cylinders and/or pistons and state which version you have 'high' version piston with the 40mm rod OR the 'low' version with the 38mm rod.

The main stud locations are the same for the 40mm & 47mm piston hence you can use either jugs on the same crankcase, but due to the larger 50mm piston on the larger version, the stud locations are wider apart and hence are not interchangeable with the other two sizes.

Hope that helps.
All this information is on this site all ready, and properly explained. First there are no 49cc ( 2 stroke) bicycle engines they are 48cc or 50cc depending on stroke as the 38mm stroke and 40mm piston equal 48cc's and the 40mm stroke and 40mm bore equal 50cc's. High hole and low hole pistons are used with both strokes it just depends on the model, the 39.5mm stroke is only the high hole piston from manufacture. The stud spacing for a 48-50cc engine is NOT the same as the 66-69cc and again the 50mm piston variants have a larger spacing, you can't put a 66-69 jug on a 48-50 case or vise versa. The high and low hole pistons are used in both strokes and this doesn't change the displacement at all, many people have mixed and matched stroke, piston type and cylinders with out any issues when you know what your doing.
 
Just about everywhere in the world measures displacement by cc's, except China way over exaggerates these engines for marketing purposes I'd guess but here's the real deal, most engines marketed as 80cc bicycle engines are actually 65.93 cc's with a 38mm stroke and 47mm bore or 69.4cc's with a 40mm stroke and 47mm bore, the 48cc engines are 38mm stroke and 40mm bore with a 50cc being 40mm stroke and bore, then the 100cc engines are similar in having a 38mm stroke and 50mm bore which is 74.61cc's these are the bt and yt versions and a 40mm stroke with 50mm bore is 78.54cc's, and what difference does this make? In the variants with 2mm of stroke difference not much really and the difference between 48 and 78 cc's well it's pretty obvious more displacement makes more torque and therefor useable power in theory but then herein lies the problems of tuners world wide, what do you want to get from the engine, torque monster, screamer or somewhere in between? while displacement with big bores can improve torque output it's usually at the cost of rpm gains because it's harder to turn more reciprocating mass and not do damage to other internal parts such as the wrist pin it's bearing and the big end bearing along with the crank bearings and even connecting rod itself, an engine that has more bore than stroke is referred to as being over square and over square engines are not considered as good high rpm engines mainly due to the afore mentioned but are great torque monsters over a narrower rpm range. The normal 2 stroke is slightly over square and can be made to still have decently higher rpm but again this comes with a cost of losing torque due to having to highly alter port timing and changing the flow characteristics to better suite the higher rpm range. A square engine like a true 50cc with equal bore and stroke of 40mm and lower reciprocating mass on the same weight crank as the larger 66-69's will rev to the moon and get there quick if not over loaded while lasting much longer doing so. It's all about what you want to get from the engine that should direct your research in getting there.
That is the best reply I've ever seen on any of these threaded. !! With that said I have a question if you don't mind. It's about bottom end bolt spacing between the 80cc , the BT100, and the Yd100 . Are the case specifications the same and the internals the only difference or do different manufacturers alter the molds to their own specs. The reason I ask is because I am replacing the top end on my bt100 but parts are basically impossible to find. YD100 parts are pretty easy to locate and then just general replacement parts are out there too.
 
That is the best reply I've ever seen on any of these threaded. !! With that said I have a question if you don't mind. It's about bottom end bolt spacing between the 80cc , the BT100, and the Yd100 . Are the case specifications the same and the internals the only difference or do different manufacturers alter the molds to their own specs. The reason I ask is because I am replacing the top end on my bt100 but parts are basically impossible to find. YD100 parts are pretty easy to locate and then just general replacement parts are out there too.
The best idea is to ask the seller for the measurements.
 
That is the best reply I've ever seen on any of these threaded. !! With that said I have a question if you don't mind. It's about bottom end bolt spacing between the 80cc , the BT100, and the Yd100 . Are the case specifications the same and the internals the only difference or do different manufacturers alter the molds to their own specs. The reason I ask is because I am replacing the top end on my bt100 but parts are basically impossible to find. YD100 parts are pretty easy to locate and then just general replacement parts are out there too.
No unfortunately all three are slightly different, the bt 100 is it's own redesigned Zeda creation with alot of different parts and the yd 100 still uses the same crank, ignition, and externals as the 80's but the bolt circle dia for the cylinder studs and the base/transfers are different again.
 
No unfortunately all three are slightly different, the bt 100 is it's own redesigned Zeda creation with alot of different parts and the yd 100 still uses the same crank, ignition, and externals as the 80's but the bolt circle dia for the cylinder studs and the base/transfers are different again.
Thank you . I used the measurements on the eBay listing to compare with my motor and they appeared to be the same so I ordered top end kit. If they don't work I can return them. Or maybe my internal parts might jive with a new bottom case that works with the new jug. One way or another I will get this thing working correctly. I'll find a way to get in touch with zeda in the meantime.
 
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