To 100cc or not... Brief break down of different "types" of 100cc (50mm piston) motors

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Wevil Kenevil

Well-Known Member
Mar 4, 2022
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Sack a tomatoes California
I know that most of you are aware of the slight but drastic differences in the different types of 50mm 100cc set ups but being new to this motor, I found it a hassle to learn the differences and their strong points and draw backs.

And PLEASE correct me if I am wrong but there are 4 types.

I originally bought a pexmor 50 mm 100cc kit. Well when I opened it up I was shocked to see what a horrendous job they did matching parts to their counterparts.

Beware, MOST OF these bicycle kits are just 46-47 MM piston motors honed out to 50mm. With NO real signs of upgrading the hardware to help

The problem: Thin cylinder walls and uneven hone. Mine looked like someone fell asleep leaning on the cylinder while boring it out.

Up side: it's cheap, and upgraded parts are readily available if you blow it up.

And You get to taste what the yd- Ld- and BT are about. Danger this is addictive !


2. The LD100 cylinders flood the market for 25 dollars and up depending on the package you buy.

I bought the LD 100 cylinder/ piston/ rings/wrist pin bearings/needle bearings , c clips/wrist pin and BEARING SPACERS***and gasket to replace the funky cylinder I got with the piece of crap pexmor kit ...

Only to find out the case that it fits is a bit larger than the standard c.g.

The bad thing about these is the mating surface on the cylinder for the intake and exhaust are EXTREMELY THIN. THE EXHAUST PORT ON MINE IS 3.4 MM THICK.

AND the hole is wayyy wider than any exhaust that I've seen other, than the inset flange on the BT which still don't fit.

Crappy design but does have G4 open ports and looks 1/3 bigger than its lil brother. And Unless there is some miracle work around for the exhaust that I am UN aware of I say skip it. The higher compression head cost me 60 USD for this. The ports don't match up to most standard parts.

(I don't see a draft save so I will finish this at my next free moment) sorry.
 
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Wevil Kenevil

Well-Known Member
Mar 4, 2022
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268
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Sack a tomatoes California
The next head is the one piece yd cylinder.

I haven't had the chance to run one but from everything I've read and just by looking at it, it looks like it would overheat quickly and because the top is one piece would make it hard to port. No squish band adjustment and aluminium cylinder sleeve just isn't that durable.

Maybe someone has something positive to say about them but if they do I haven't run across it yet.

And last but not least the BT head... All I know about these is that it has an inset exhaust pipe that fits inside of the cylinder and I'm not too sure that that is a good idea does anybody have any input on that but it's too specialized and only one type of exhaust pipe that fits it.

If I've misstated anything or missed anything please feel free anybody to add to what I've said.
 

tommygunn1488

New Member
Mar 6, 2014
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4
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SANTA CRUZ ,CA
i built an electric start BT100 great power i left the end cap off the pipe ,louder but enuff gain you could FEEL the difference the way the pipe fits is very much like older japanese motorcycles and its exactly the way the pipes fit the evo motor in my chopper seems to work just fine gonna change the flange on one of my arrow pipes so i can use it wit the BT
 
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Wevil Kenevil

Well-Known Member
Mar 4, 2022
294
268
63
47
Sack a tomatoes California
i built an electric start BT100 great power i left the end cap off the pipe ,louder but enuff gain you could FEEL the difference the way the pipe fits is very much like older japanese motorcycles and its exactly the way the pipes fit the evo motor in my chopper seems to work just fine gonna change the flange on one of my arrow pipes so i can use it wit the BT
How much of the muffler did you chop?
 

jannickz

New Member
Jan 4, 2024
3
3
3
28
I know that most of you are aware of the slight but drastic differences in the different types of 50mm 100cc set ups but being new to this motor, I found it a hassle to learn the differences and their strong points and draw backs.

And PLEASE correct me if I am wrong but there are 4 types.

I originally bought a pexmor 50 mm 100cc kit. Well when I opened it up I was shocked to see what a horrendous job they did matching parts to their counterparts.

Beware, MOST OF these bicycle kits are just 46-47 MM piston motors honed out to 50mm. With NO real signs of upgrading the hardware to help

The problem: Thin cylinder walls and uneven hone. Mine looked like someone fell asleep leaning on the cylinder while boring it out.

Up side: it's cheap, and upgraded parts are readily available if you blow it up.

And You get to taste what the yd- Ld- and BT are about. Danger this is addictive !


2. The LD100 cylinders flood the market for 25 dollars and up depending on the package you buy.

I bought the LD 100 cylinder/ piston/ rings/wrist pin bearings/needle bearings , c clips/wrist pin and BEARING SPACERS***and gasket to replace the funky cylinder I got with the piece of crap pexmor kit ...

Only to find out the case that it fits is a bit larger than the standard c.g.

The bad thing about these is the mating surface on the cylinder for the intake and exhaust are EXTREMELY THIN. THE EXHAUST PORT ON MINE IS 3.4 MM THICK.

AND the hole is wayyy wider than any exhaust that I've seen other, than the inset flange on the BT which still don't fit.

Crappy design but does have G4 open ports and looks 1/3 bigger than its lil brother. And Unless there is some miracle work around for the exhaust that I am UN aware of I say skip it. The higher compression head cost me 60 USD for this. The ports don't match up to most standard parts. I should check Tradbearings.com

(I don't see a draft save so I will finish this at my next free moment) sorry.
I appreciate your cautionary tale and helpful information. Choosing the right 50mm 100cc kit can be confusing, especially for newcomers. Your detailed breakdown of drawbacks and alternatives will definitely help others avoid pitfalls and make informed decisions.
 
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