DT125R FORUM

Greetings to all of you and thanks for loads of information on the dtr 125 engine. My project is my first bike, a 97 KTM lc2/ sting with the minarelli/Yamaha engine. Now I have been struggling a bit with this one, my piston got a hole in it and the plug electrode disappeared. You have some good knowledge here on the forum, really appreciate it and thanks to contributors. My problem seems to be a stroke length of 56mm, not 50,68. With my new 125 Athena kit I have measured squish being 1,1mm. The piston will almost open the exhaust port, half a mm being visible. Special thanks to Calum for posting the video of the bore of the 170 Athena kit. Really helpful video for me in this case. I will try post pictures and share what I learn from my mistakes with my KTM. Also, I own a 87 rd350 ypvs in bits and pieces, so please accept me as the true Yamaha enthusiast I am.

This is my project, my first motorcycle. The bike has not been running for the last 15 years or so because engine problems. I went to get it this summer at my uncles house. He had fitted a rd 125 piston with holes on the skirt. I burned a hole in that one before i washed the crankcase thorougly and put it together with an athena 125 kit. The other piston is from the time my brother had a engine seizure.

There is many possible reasons why this happened:
1.the stroke length being around 56mm giving me around 134ccm.(and different compression ratio)
2.water pump axle being jammed into crankcase causing a warped nylon gear and insufficient cooling.
3.Missing reed stoppers. I have boyesen dual stage reeds w/out stoppers.
4.A mutilated air filter box. There is extra holes in it.
5.air leakage somewhere
6.Lean jetting is probably not the case because I have really made sure to be on the safe side.
7. Aspen alkylate fuel. This does not have the required octane. This fuel did not cause the first seizure(as it was not available here at the time)

Now I decided to try again! This time with 98 octane premium fuel, rich oil mixture, and I got a cheap koso water temp gauge for safety.
I am going to fill the combustion chamber with oil at tdc, measure the volume and find the actual compression ratio. I have a original KTM expansion chamber without cat and restriction ring. The other restrictor was a plate behind the air filter.

Any hints or tips would be much appreciated.