OzVMX Forum

Marque Remarks => Yamaha => Topic started by: POM on November 21, 2015, 10:39:59 am

Title: Yz490 piston
Post by: POM on November 21, 2015, 10:39:59 am

Does anybody know the difference between the 82/83 piston and 84 onwards?.......part listings on eBay seem to suggest their different.......

Title: Re: Yz490 piston
Post by: tony27 on November 21, 2015, 12:23:09 pm

Likely to ring pin location, earlier motors are sideport like the 465s then then they changed to central exhaust port. Reed valve shape changed as well

Title: Re: Yz490 piston
Post by: Rupert Prior on December 28, 2015, 02:45:39 pm

there is a difference in the compression heights (pin to crown height). early is 40mm and late is 39mm, I don't know the point they changed and I have only seen it in after market pistons. it causes problems with the squish clearance, so the barrel has to be shimmed to match.