HELP Measuring cylinder clearance - WR250F

[WRossiF]

Hi Guys,

 

I´ve just opened my engine and found some weird measures. I would like your opinion to see whats wrong. It´s a 2008 WR250F, never opened. Engine was untouched, so by the time thats it was running, it was already on time for a preventive.

 

On the top of the cylinder i have 77.05mm. Just below it, like 5~8mm below, my cylinder has a "tooth", like a depression of 2mm of height. It´s located on the top, exactly where the first rings stays when the piston is facing the top. The diameter on this depression is 77.12mm.

 

Below that I have 77.02mm on all cylinder. When I turn the cylinder around, i got a reading of 77.05, but thats a minor spot. So I think that my "out of round" limit is okey, 77.05 - 77.02 is 0.03mm, inside the limit of 0.05.

 

But now i have a doubt of how to measure the clearance. Should I use 77.02, the main measure of my cylinder, or the biggest measure, even if it is a spot, of 77.05??

If I take the measure of 77.02, my piston is @8mm of skirt with 76.96, so my clearance is 0.06, still normal, but out of the "good" margin. A piston "C" would take back to 0.05.

But is this right? The measure that i should take is 77.02 or 77.05?

 

The reason that i think the tooth on the cylinder exists: the piston pin bore was slightly damaged. It was lacking a little bit of material. The bore size is 16.002, and the limit 16.043. My pin bore was 16.16, so I think that was the cause of the piston "dancing" inside the cylinder. Since it was just a small depression of 2mm, i think I will leave it there....

[William1]

Sounds like a bad case of over analysis.

 

The top of the bore is glazed and carbonized. Clean it with a scotchbrite. If the crosshatching is worn away or there are nicks, it is time for a replate.

 

 

Piston sizes are for matching to a replated or new barrel. Not to stretch the serivice life of an already worn out one. Do a barrel swap with Millenieum Tech and have them suppy a fitted piston and rings.

[WRossiF]

Sounds like a bad case of over analysis.

 

The top of the bore is glazed and carbonized. Clean it with a scotchbrite. If the crosshatching is worn away or there are nicks, it is time for a replate.

 

 

Piston sizes are for matching to a replated or new barrel. Not to stretch the serivice life of an already worn out one. Do a barrel swap with Millenieum Tech and have them suppy a fitted piston and rings.

My mechanic said that the top of the cylinder is were it wear more... And if I get a C size piston, the ring could get stuck on the worn top-part and damage even more...

 

So i decided to stay with the bike and got a Athena 290cc kit... The Cylinder Works was almost 40% cheaper than Athena, is it good???

[William1]

Cylinder Works are good kits.