10 450 valve to piston contanct

2 replies to this topic
  • danzick

Posted March 10, 2014 - 11:18 AM


so I bought a used 2010 450 during the fall. I threw it in the shed during snowmobiling season. Well i decided to take it out and take it apart and rebuild it fresh for this coming season. I pull the head to find what looks like all 4 valves hit the piston, but it looks like they only hit just once. Did the previous owner not set the timing right before trying to start it? I would think if they hit while it was running, there would be more damage. bike ran fine when I tore it down. I put water in all of the ports to see if the valves leaked at all, but the valves didnt leak, so I dont think they are bent. Another mystery, I see its a vertex piston, and it has a cylinder works cylinder. It appears to me that the companies are linked in some way. Im wondering if he had a bad issue and lost the factory piston and cylinder. Do some people order a new cylinder while they are doing a piston? I never have. Just trying to clear up a few mysteries about this bike. I guess one plus, the valves were in spec.





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  • grayracer513

Posted March 10, 2014 - 11:51 AM


What it looks like is that the piston was installed backward.  It looks as if the valves overhung the edges of the cutouts and contacted them.  The flycuts are centered differently for each pair of valves, and a reversed piston looks like the most likely cause of the valve contact.


What may have caused this is that arrow mark.  The OEM Yamaha piston is stamped with an "F" that belongs toward the front.  The majority of aftermarket pistons are made with marks that go toward the exhaust side of the engine, and judging by the cutouts on this one, I would say that it was marked with the arrow to be facing the exhaust side.  That, of course, is the rear on this particular engine, so there may have been some confusion about this point when it was assembled.

  • danzick

Posted March 10, 2014 - 02:39 PM


I agree. A friend of mine and I were looking at it, and that is what we came up with as well. Probably used to having the exhaust side towards the front of the bike, so they installed it backwards. Thanks! just wanted to make sure everything was ok before putting a brand new piston in it. Still wondering why he had to buy a new cylinder.

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