426 cranks

I sold a buddy a 2001 yz426 and after about 10 rides he lost the big end bearing.He went to have all the parts ordered to get it fixed and the Yamaha dealer here told him if he had know he was buying a 426 he would have told him to stay clear as the crank failure is a common problem with these bikes.Is this true with the 426's?I haven't heard anything about bad cranks in the 426.We are in the process of rebuilding the bike and I even offered to pay for some of the parts,plus I'm doing all the work for free.I had allways used the yamalube 20w/50 in the bike but when I bought the 450 I started to use mobile 1 mx4t so my buddy started also,it was on his first oil change that the bike failed.I doubt the oil caused the problem but the Yamaha dealer told him not to use synthetic oil in the bike,I think the dealer here is full of it but wanted you guys thoughts on his comments.

I have run semi synthetic Valvoline "ATV" 10w/40 with no issues thus far on my 02 426. I have never heard of any serious defects or issues with the 426's and I doubt the Mobil oil change is why it failed as well...

Whoever told you not to run synthetic oil should never be asked for advice of any kind, ever again.

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