Convert DT300 to DT350

[izmircephastanesi]

Hello guys, i m from Turkey and fan of Kymco. I've a 2010 downtown 300, needs an engine rebuild. I really wonder, if it is possible to rebuild the engine by DT350 Cylinder and piston set. They look very similar.

[CROSSBOLT]

You may be the first to do this! Those part numbers have no LEA7 tags so one would think they are the same.

[francuz69]

Don’t know about Kymco since DT300 i have recently bought is my first Kymco.
But i know how Piaggio evolved from 200 to 250 cc, so maybe this info will be something you can use.
Piaggio kept exactly the same piston regarding diameter, but crankshaft was larger in circling diameter and it’s connecting rod was longer, hence the piston is traveling more. So combustion chamber grew up from 200 to 250 cc.
Unfortunately, that does not mean that you can use piston from 200 on 250 and vice versa, because intake and exhaust ports can not function properly with camshaft from other type of engine.

[mousejunks]

I have owned the DT300 and currently own the DT350. Compared to each other they internally are very similar. 

The engine of the 350 is actually 321cc not 350cc as implied by the name. The bore of the 350 has been widened from 72.7mm to 75.3mm, however the stroke remains at 72mm. The transmission is identical and so are many of the engine parts.

The 300 uses the code LEA7, the 350 uses ACD5. The ECU is also different as well as the voltage regulator.

[francuz69]

Sorry for my English, sometimes i can't find the right word at the moment.
Yes, Mousejunks i was talking about stroke in Piaggio.
So, if DT300 and 350 have the same stroke but different bore, maybe it would be possible to put DT350 cylinder and piston on to DT300 engine.
I guess that someone must be the first to go down to the trial/error path. Until someone tries, others won't know will it work or not.

[CROSSBOLT]

Sorry for my English, sometimes i can't find the right word at the moment.
Yes, Mousejunks i was talking about stroke in Piaggio.
So, if DT300 and 350 have the same stroke but different bore, maybe it would be possible to put DT350 cylinder and piston on to DT300 engine.
I guess that someone must be the first to go down to the trial/error path. Until someone tries, others won't know will it work or not.

Your English is fine! And you are exactly right!

[KymcoRockr]

Make sure they haven't changed the wristpin diameter. Leave the battery disconnected for a while and hope that when you plug it back in, the ECU can recalibrate for the change in displacement. If it won't, you might need something like the Malossi Forcemaster to get enough gas to it.

[de dee]

If you are replacing the cylander for 21 cc.s would it be better to wait for the X 360 to get more power ,.  if that would fit ,  likely change of drive shaft and piston,