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jake27

yz426 engine question

6 posts in this topic

I blew my 426 up and just got all of the parts back that I needed to fix it.I got a new head and cylinder along with Kibblewhite valves,I had the cylinder bored and plated to a 440 and had the head ported, I also installed a Wiseco high compression piston. I used my Hot cams intake and auto decompression exhaust cams that I already had in the bike.I know I have the engine timed right and the proper thickness gaskets installed, the problem is one or more intake valves are hitting the piston. I talked to the shop that did the work on the head and cylinder and they said the pockets on the piston for the valves might not have been right from the manufacturer and may need to be machined. Has anyone ever had this problem before or heard of anyone else that has had a similar problem? I plan on claying the valves to see where I am having the clearance problem but would like to get some input to see if anyone else has had this happen to them, thanks, Matt

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You need to contact hot cams there is a very good chance that the cams will not work with your piston setup. Also if your out by 1 tooth on the stock cams the valves will hit. But I'm pretty sure that that combination will not work.

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I just did a ton of motor work to my 250r yz hybrid, I was having problems with a knock that I just couldn't figure out. I talked to everyone I was also running wiseco hot cams and a 440 kit/ I thought it was valve noise I called wiseco and they said if you run their pistons with their cams it will work, I puddied it and it was plenty of clearance, doubled the base gasket like east coast said and still couldn't figure it out. Finally I realized that a yz426 gasket on a 96.5mm piston (even though it says it will fit) needs to be opened up with a drum sander the piston was taping the head gasket not the valves. Maybe that will help

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I haven't had any time to work on it yet.Hopefully I will get to it this weekend, Thanks for the input guys, Matt.

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