Ciao everybody,
I'm Luca from Italy and I ride an EC 250 my 2005.
I joint the forum as I've read lot of interesting and useful info. Thanks to administration and to you all to share. Despite several threads here on the forum about this topic, I didn't find an answer, so I try to ask you help. This is the first thread, please be patient.
I've opened the engine to have a look to the piston/cylinder. It's the first time for me for this operation:
Piston is a Vertex "B", 66,34. Measuring it, I found 66,28 on the bottom, 66,19 on the top. I don't know how many hours it has, surely over 40, most probably around 100.
Cylinder bore seems to be 66,35. I measured several times both piston and cylinder as these numbers sound strange compared to the nominal ones, but I always found comparable values.
Do you think they are reasonable? Or measurement is not my job?
Because now I don't know if piston should be changed or not. For the aspect I can post come pics end of the week. I can say you only that is blackened under the rings both on cold and hot sides, but finishing is still ok and cylinder appears in a good shape (still row present and no scratches).
To end, more in general:
1. On the manual I see that standard bore is 66,4 and it may be up to 66,9. Considering that I find pistons of only 3-4 dimensions, from 66,33 to 66,36 mm and suggested clearance is 0,05-0,06 mm? do I have to think that manual is wrong? Otherwise how?s it possible to have up to 0,5 mm of clearance??
2. Measure indicated on the piston, i.g. 66,34 means piston diameter? Does it mean that mine that?s 66,28 is so worn? And if my cylinder is only 66,35, which piston should I chose??
I?m a little bit confused.
So thanks to whoever may help me and sorry for my english!!
I'm Luca from Italy and I ride an EC 250 my 2005.
I joint the forum as I've read lot of interesting and useful info. Thanks to administration and to you all to share. Despite several threads here on the forum about this topic, I didn't find an answer, so I try to ask you help. This is the first thread, please be patient.

I've opened the engine to have a look to the piston/cylinder. It's the first time for me for this operation:
Piston is a Vertex "B", 66,34. Measuring it, I found 66,28 on the bottom, 66,19 on the top. I don't know how many hours it has, surely over 40, most probably around 100.
Cylinder bore seems to be 66,35. I measured several times both piston and cylinder as these numbers sound strange compared to the nominal ones, but I always found comparable values.
Do you think they are reasonable? Or measurement is not my job?
Because now I don't know if piston should be changed or not. For the aspect I can post come pics end of the week. I can say you only that is blackened under the rings both on cold and hot sides, but finishing is still ok and cylinder appears in a good shape (still row present and no scratches).
To end, more in general:
1. On the manual I see that standard bore is 66,4 and it may be up to 66,9. Considering that I find pistons of only 3-4 dimensions, from 66,33 to 66,36 mm and suggested clearance is 0,05-0,06 mm? do I have to think that manual is wrong? Otherwise how?s it possible to have up to 0,5 mm of clearance??
2. Measure indicated on the piston, i.g. 66,34 means piston diameter? Does it mean that mine that?s 66,28 is so worn? And if my cylinder is only 66,35, which piston should I chose??
I?m a little bit confused.

So thanks to whoever may help me and sorry for my english!!
