Piston and bore size

Pulled my 94 cr250 engine to bits for major overhaul, but curious on top of piston there is a number 1 does this tell me what size piston is?

I'm not really sure about o.e.m. markings. You might see an A or a B stamped on there. The piston should read 66.3? If it is aftermarket. The question mark would vary with bore size. Anywhere from 66.33 mm on up.

Where are you at in NZ? I lived down in Christchurch in the 80's. (wow, does that date me or what?)

Edited by GustavMiller

Just wanted to add something. You really should take the cylinder to a machine shop and have it measured. You need to base the piston size on the bore and not the old piston.

Are you sure that the 1 you are seeing is not actually the arrow indicating forward direction?

Edited by GustavMiller

Just wanted to add something. You really should take the cylinder to a machine shop and have it measured. You need to base the piston size on the bore and not the old piston.

 

X2, though with a plated cylinder it SHOULD be around 66.3''

X2, though with a plated cylinder it SHOULD be around 66.3''

Question for you DirtRider. On my KTM, you can clearly see grey NicaSil coating on the cylinder. On my CR, the bore is as shiny as can be and does not look like it's coated. Do ya think my cylinder may have been sleeved? Machine shop told me it's standard size bore.

Question for you DirtRider. On my KTM, you can clearly see grey NicaSil coating on the cylinder. On my CR, the bore is as shiny as can be and does not look like it's coated. Do ya think my cylinder may have been sleeved? Machine shop told me it's standard size bore.

 

Nickisil is a clear coating, the color differences could be due to age and a different compound of the cast metal. If you look at the top and base of the bore, you should be able to see a distinguishable ring to show that there was a sleeve. If there is no distinguishable ring, there's no sleeve.

Hi GustavMiller, I'm in Dunedin in New Zealand, you will be pleased not in Christchurch last couple years they have had it rough with earthquakes what suburb of Christchurch were you in?

Also does anyone have any pics or info on porting 94cr250 or hints because I'm also about to do this

if you have never ported. dont do it. you can junk a cylinder in a hart beat. that #1 is probebly the arrow showing you witch way the piston needs to be installed.

Hi GustavMiller, I'm in Dunedin in New Zealand, you will be pleased not in Christchurch last couple years they have had it rough with earthquakes what suburb of Christchurch were you in?

I lived in Avonhead, then Burnside and finally Riccarton. I friend of mine down there sent me some photos of the damage downtown. Dude, I can't believe the cathedral is gone!!!!!! That place got destroyed. It's really sad.

Dose anyone have parts for a 94cr250

Just wanted to add something. You really should take the cylinder to a machine shop and have it measured. You need to base the piston size on the bore and not the old piston.

Are you sure that the 1 you are seeing is not actually the arrow indicating forward direction?

 

 

Yes take it to get diamond honed, inspected and measured for the correct piston size. Especially with a bike that's over 20 years old. The place I take my cylinders to charge only $30 for all that. Money well spent.

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