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honda cr 250 2002

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i have a honda cr 250 2002 ,and ive had to rebuild in twice in the last two month,,the reason for this is that piston keep breaking in the barrel at the front by the power values,,,ive had the cylinder sleeve replaced and i just want a good runner again,,the jetting seems fine,and i allways use genuine honda parts ,,it a lways break at the the front by the power values

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What part of the piston is breaking? Is it breaking at the top near the rings or at the bottom near the skirt?

I've got a couple of causes for your. If it's failing near the rings, that's because the ports in the new sleeve weren't properly chamferred and the piston ring is snagging in the port causing the piston to break.

If the piston were installed backwards, that will also cause the rings to snag. The arrow points towards the exhaust or forwards. But, this snag usually happens the first time the bike starts.

If the failure is near the bottom of the piston, in the skirt, I would suspect a clearance issue. You need to accurately measure the bore of the cylinder and measure the skirt of the piston. The difference between the two measurements should be .0015"-.003" with a new piston. If it's any larger, this will cause the piston skirt to rapidly fatigue and fail.

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did you get your cylinder bored out bigger? If so did you get the powervalve machined to clear the piston? Piston may be hitting the powervalve.

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Stock pistons say IN on the top and the IN should be toward the intake side. Aftermarket pistons have an arrow that typically points toward the exhaust port. And +2 on the chamfering.

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What part of the piston is breaking? Is it breaking at the top near the rings or at the bottom near the skirt?

I've got a couple of causes for your. If it's failing near the rings, that's because the ports in the new sleeve weren't properly chamferred and the piston ring is snagging in the port causing the piston to break.

If the piston were installed backwards, that will also cause the rings to snag. The arrow points towards the exhaust or forwards. But, this snag usually happens the first time the bike starts.

If the failure is near the bottom of the piston, in the skirt, I would suspect a clearance issue. You need to accurately measure the bore of the cylinder and measure the skirt of the piston. The difference between the two measurements should be .0015"-.003" with a new piston. If it's any larger, this will cause the piston skirt to rapidly fatigue and fail.

Good info +2 on checking your tolerences when doing a topend.:thumbsup:

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ive had two different companys fit the sleeve and only had 6 rides last time,,spoke to another company and they said its a common problem with this bike ,,,is there anyway to sto it?

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6 rides for a piston isn't common for anything but a bike doing the Baja.

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Sleeves are a horrible way to go, they don't dissipate heat as well and get hot spots.

Something is wrong, and I have found stock honda pistons in that bike wear out fast, not break but wear out fast. (i have 2 seasons on that bike)

The exhaust bridge is a problem area on all cr250s, if you sleeve it I imagine the heat build up would get worse.

My 02

4saleagain003.jpg

topend5.jpg

pistonkholes.jpg

I had my cylinder welded re plated and then honed to spec. I also went through three oem piston sets before going wiseco, and I would get 2-4x the hours of of a wiseco unit over a stock.

Don't waste your money on oem junk.

How hard do you ride the bike? What kind of oil do you use and at what ratio?

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Normal 2 stroke oil?

And mix at 32:1 at least, 310ml of oil per 10liters of fuel (31ml per liter)

And what Kind of oil? I would use a quality synthetic (amsoil dominator, motul, klotz, maxima k2)

Once everything is fixxed and in spec, get a wiseco piston and drill the piston where it passes over the exhaust bridge, it will allow oil/fuel to cool that problematic exhaust bridge.

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What you see in the picture isn't a failure. That's normal for exhaust bridged 2-strokes. If you're getting a significant flat spot in the piston you need to relieve the bridge. Clearance in the bridge area needs to be an additional .003-.004" over the piston to cylinder clearance. You can do the clearancing with a die grinder and sanding wheel. I recommend soft sanding wheels because they blend the edges better than using a hard burr.

Oh, stock or Wiseco, try drilling the cooling holes.

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To clearance the bridge, remove material from the area outlined in red.

02cylinder.jpg

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