I just noticed that the cut down 300 pistons both failed where they'd been cut down. I'm glad I'm now going for the ones that haven't been cut down, but I take that this is a common problem with the ART cut-down pistons? As I haven't raced it or been hard on it...
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MC21 Honda NSR250. TYGA 300 conversion.

We only had two ART pistons crack. Both down from the drilling over the exhaust bridge.
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If I have to take the carbs off once more...

Mine cracked on the exhaust side. The crack starts at the base of the skirt and makes its way up through the two little oil holes. The 'standard' cast pistons that come with the kit are from a Kawasaki engine allegedly. I did the crank case mod and ran some cast pistons with full skirts for a while (because Matt@Tyga was struggling to get a new supply of forged pistons at the time) and they were fine when i took them out to swap over to the forged items. I should point out that mine is a dedicated race bike and therefore gets thoroughly abused as such. So don't panic if you've got unequal skirted pistons in your street bike's motor. If you want the piece of mind then the process of modifying your crank cases to accept full skirted pistons AND advice on how best to order them specially from Tyga are documented in an old thread on the forum here. Just use the forum search function.

I should also point out im not writing this as a direct reply to the OP but as a message to people using the search function to find help in future.
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After years of moaning about immigrants now i am one...

Stephen, are you saying the crack started from the holes drilled? I'm wondering if they even need to be drilled. Aren't the NSR150 cylinder exhaust bridges relieved?

Yeah both ours cracked down from the holes, we then got new pistons with no holes and tried drilling just one hole (as I recall the first ones has 2 holes). These also cracked. I never ran a ART piston with no hole so can't say if that would of cured it.

Soon after that TYGA started supplying the Wiseco. We started using Wiseco piston but had trouble with the crowns. I moved back to 250's so stopped do any real work after that.
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If I have to take the carbs off once more...

That's a shame. Mine do have two holes drilled :S

I have run cut wiseco's and cut cast pistons with good results . I used the cast pistons while the new wiseco's were being made . I did 600km of hard racing on the cast cut
pistons and can show a picture of what they look like . I changed them to be safe but looking at them you would say they are good to go . My new motor runs full skirt wiseco's
with no problems . What i do is double check bore clearance , ring gap , counter sink oil holes , warm it up before you blast it etc .

Neal wrote:I have run cut wiseco's and cut cast pistons with good results . I used the cast pistons while the new wiseco's were being made . I did 600km of hard racing on the cast cut
pistons and can show a picture of what they look like . I changed them to be safe but looking at them you would say they are good to go . My new motor runs full skirt wiseco's
with no problems . What i do is double check bore clearance , ring gap , counter sink oil holes , warm it up before you blast it etc .

Please post pictures...

Haha , those pistons went into the scrap box long ago for recycling !
I think I still have the wiseco ones that replaced them , they have been replaced too after burning 200l of race fuel and look good .
My new wiseco's have done 30l now so this time I will run them a bit longer