That's true; I forgot to ask how many miles are recorded on the odometer. ;) Has the engine lost power, or is the engine burning oil? If neither case is true, I would hone the cylinder, clean the piston, and install new piston rings and new gaskets. :) However, I would still clean the inside of the cylinder head, lap the valves, and purchase new valve stem seals. ;)

No, that photograph of the cylinder head is inverted. The area just below that imperfection is where the cam chain descends to the crankcase. ;) I don't think that imperfection is an actual hole, or anything to worry about. It appears to be a minor imperfection in the casting. :shrug:

It has 27,500 miles, lost power a bit (will not go beyond 90 km, used to go up 100 km). Burning oil? I would say no.

Weld, the cylinder is not scored but there is a ridge in one side at the top.

Based upon your answers, I think you are wise to bore and hone the cylinder as you planned. :)

Agreed. That's a considerable number of miles.

Spud, what piston size I should order from Yamaha TW200 (0.5, 1 mm, or standard) I measured the cylinder (X 66.54 and Y 66.59 mm at 15 mm from the cylinder top not as the manual says 40 mm) and piston skirt diameter (67.09 mm). The piston-cylinder clearance is obviously greater than 0.1 mm limit and not sure the piston size I need. There is number at the piston skirt (inside) I can´t read. The guy at the shop ask me for the this number to get the next size before rebore (my fault I did not take the piston to the shop but I will this fri).

Thanks

One should always take the new piston to the machinist before he bores and hones the cylinder. If a competent machinist has the new piston, he should be able to do the job correctly. ;)

Hector, it is a good idea to choose the smallest diameter you can, so you have more bore options in the future. Take your cylinder and piston to the machine shop to get their opinion.

I went to Yamaha dealer and bought the 0.05mm piston, rings, and clip, parts will arrive in 40 days (last time I bought the gaskets, they arrived in 20 days). Meanwhile, I dropped the cylinder head at the shop for cleaning and seat valves. I am getting rid of dirt (oil and dust in the rear arm) and will send all plastics and gas tank for painting in red (gas tank) and white (all plastics) although the frame is black (the saddle is red color). Any suggestion? Also, I will reduce in length the exhaust 20 cm because the turn signal always get dirty. I am taking advantage of winter and am not in a rush of doing everything in one shot.

Saludos chineros (chineros are called people who ride a chinese bike).

You are making good progress. I suggest you also order a new piston pin, which connects the piston to the connecting rod on the crankshaft. ;) The piston pin is part #10 in the following diagram.

http://images.powersportsnetwork.com...HAFTPISTON.gif

The piston pin is Yamama part #58L-11633-00-00.

Got it already, I forgot to mention.

Hector, where is it winter in Mexico? I'm sitting in PV right now, and it is beautiful outside. I think it is about 28C.

Chineros! I love it!

If you´re in Puerto Vallarta (PV, not sure what PV stands for) what a lucky chinero you´re. Here in Chihuahua (north of Mx) temps are between 0-5C by morning and around 10-15C at noon. I love riding when temps are above 20C. I spent my winter vacations in PV, 2013 and hopefully will spend a couple of days in Cancun next late-March.

Saludos

I was actually north of Puerto Vallarta, in Bucerias. I'm home now, and it is 8C here right now; not too bad.