1993 kx 80

Hi,

I had a 1993 kx 80 that I sold recently that had a 101cc bigbore until the exhoust bridge cracked then I brought it back down to a 80cc.And the piston would last about 7 hours when was a 101cc and a 80cc which I think that is normal for a 80. But the crank would only last about 15 hours is that normal. I thought cranks last at least 50 hours am I wrong.

Thanks