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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
2001 Yz250-300 Big Bore
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[QUOTE="EricGorr, post: 486469, member: 19611"] The 69.5mm bore uses a Wiseco 526MO6950 and welding and narrowing of the rear transfers needs to be done. That limits the top end and targets the low end. The 2002 cylinder casting is thinner around the cylinder walls and I've seen 2 of the 69.5s develop water leaks into the bore from casting porosities. So I've stopped offering the 275 kit on the YZ. Same thing goes for the RM 250 cylinder, the manufacturers are making their castings lean and its tough to do big bores, between the narrow margin between the bore and the inner O-ring groove to the problems with the thin castings. I think we'll see the use of aluminum sleeves in the future for big bores. LA Sleeve is making cast sleeves out of hyper-eutectic materials and Advanced Sleeve turns sleeves out of forgings from Wiseco. Of course these sleeves must be plated to be used in an engine. [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
2001 Yz250-300 Big Bore
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