Converting a EC200 to a EC300
- Thread starter Ply318ci
- Start date
stainlesscycle
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i did it, although not the way you would think. pull complete 200 motor out. place complete 300 motor in. go riding. you can use the clutch and ignition and engine covers from the 200. but the cases/crank/cylinder and head gotta be 250/300.
stainlesscycle
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cylinders will fit, stroke is 65mm on 200, stroke is 72mm on 250/300
noobi
New member
The bore, stroke and cases are all specific to the 200, whereas the 250 and 300 share cases and stroke, only the bore and piston are different. They do however share the same length rod, that of a CR250.
You could potentially make some sort of hybrid using the 200 crank, but I would guess that the 250 and 300 cylinder will be completely wrong in terms of desirable squish, and port timings.
You may be able to machine/epoxy the cases and fit a 250/300 crank, and then fit the 250 or 300 barrel, but I don't know if primary drive and all that are the same.
Would be an interesting undertaking though, possible? I would say it is, but it certainly wont be straight forward.
Maybe boring out the 200 to accept a bigger piston?
You could potentially make some sort of hybrid using the 200 crank, but I would guess that the 250 and 300 cylinder will be completely wrong in terms of desirable squish, and port timings.
You may be able to machine/epoxy the cases and fit a 250/300 crank, and then fit the 250 or 300 barrel, but I don't know if primary drive and all that are the same.
Would be an interesting undertaking though, possible? I would say it is, but it certainly wont be straight forward.
Maybe boring out the 200 to accept a bigger piston?
stainlesscycle
Site Sponsor
the cases are 200 specific, but the 250/300 cylinder mouth will fit in 200 cases.. i have a spare 200 case here and a spare 300 case here, and the mouth is the same size.
you would need to swap cranks for sure, or at least change crank flywheels due to different crank pin location. there may be machine work needed to swap cranks, dunno.
you would need to swap cranks for sure, or at least change crank flywheels due to different crank pin location. there may be machine work needed to swap cranks, dunno.
You heard wrong information. It's not easy. If you want a 300 buy one, that's the easiest way.
It is fairly easy to make a 250 in to a 300.
Caravan Monster
New member
big to small
I've been going through the old threads on the 200 to 250/300 subject - am I correct to conclude that it would not be straight forward to fit a 200 motor into my '06 300 ? [My aim is to put together a bike with a little more low / mid range than my 125 and quite a lot less everywhere than the 300. Will also enquire at TMUK about the availability of a 144 kit for my 125 as an alternate path. Anyone ride a 144 of any manufacturer ? Are they that much different to a 125 ? I dislike the process of buying and selling bikes and am trying to get what I want without going through it, if it is reasonable.
I've been going through the old threads on the 200 to 250/300 subject - am I correct to conclude that it would not be straight forward to fit a 200 motor into my '06 300 ? [My aim is to put together a bike with a little more low / mid range than my 125 and quite a lot less everywhere than the 300. Will also enquire at TMUK about the availability of a 144 kit for my 125 as an alternate path. Anyone ride a 144 of any manufacturer ? Are they that much different to a 125 ? I dislike the process of buying and selling bikes and am trying to get what I want without going through it, if it is reasonable.
GMP
Active member
200 cases/crank/primary are different than a 250/300, so you can't do a simple top end swap like a 250 to a 300 conversion. What you can do is find a 200 motor from an '05+ bike and it will drop right in your frame.
I have a 125 top end I'll sell for $100 if you want to do a big bore and keep your OEM parts.
I have a 125 top end I'll sell for $100 if you want to do a big bore and keep your OEM parts.
Caravan Monster
New member
Thanks GMP - that's very useful information about the '05+ 200 motor. I'll get the word out and see if I can find one (+carb +exhaust and probably cdi box - will check manuals)
Thanks for the offer of the 125 top end. Unfortunately my 125 is an old TM, not a GG - I was just thinking aloud
Sorry for the confusion.
Thanks for the offer of the 125 top end. Unfortunately my 125 is an old TM, not a GG - I was just thinking aloud
Sorry for the confusion.
twowheels
Active member
There may have been something missed here ... anybody know if the bottom end volumes the same between the 200 and the 250/300?
My guess, and its only a guess, is that the 200 cases have a smaller volume than the 250/300 so that the air that gets squeezed through the bottom end in one stroke is appropriate for the top end volume and compression.
My guess, and its only a guess, is that the 200 cases have a smaller volume than the 250/300 so that the air that gets squeezed through the bottom end in one stroke is appropriate for the top end volume and compression.
GMP
Active member
The volumes may be slightly different, not sure. Easy answer is measure the cases/crank wheels OD. I know the crank journals are different, as well as the main bearings, primary gearing, some transmission components, etc. You can go through the parts list and get an exact picture. If it is different, its likely not different enough to be optimal.
orangezuk,
I have this listed in the classifieds. I bought it for a future big bore project then my brother sold the 125 from under me! Its from an '03 MC125, and includes cyl., head, head stay, and all top end PV parts. Plating looks good. I'll clean it up nice and get some detailed pics if your interested.
I've been through every part of the GG125 motor. The Yamaha has some significant differences in the powervalve actuator, otherwise its close. Same with the crank, close but not close enough to save us some $$. If a YZ 144 kit bolted on the GG I would probably still have it today.
orangezuk,
I have this listed in the classifieds. I bought it for a future big bore project then my brother sold the 125 from under me! Its from an '03 MC125, and includes cyl., head, head stay, and all top end PV parts. Plating looks good. I'll clean it up nice and get some detailed pics if your interested.
I've been through every part of the GG125 motor. The Yamaha has some significant differences in the powervalve actuator, otherwise its close. Same with the crank, close but not close enough to save us some $$. If a YZ 144 kit bolted on the GG I would probably still have it today.
