Yamaha YZF450 (04) - valve problems

[MX_Peter]

Hello guys, my firs post in Yamaha thread and also first question.?

My friend bought not long ago YZF450 04 and ride it like 10h. Then he decided to sell it. Buyer came , did test ride, bike starts every time in first two kicks. He tried to start it at least 6 times. Bike run fine. They make a deal and buyer drove home with his "new" bike. The the problems came. He called my friend that he started the bike and then let it run a little. Then buyers friend drove little and he made a 180degre turn with very low rpm and staled it. He said that bike didn't want to start from that on. He returned the bike to my friend and said that he sell broken bike. As I see bike was in good condition when he sold it!

Today I went to my friend to check the bike. At first I checked valves. Both exhaust valves were little tight but not to much, intake were also good but as I know Yamaha has three valves right. I finally found Middle one, and he was way to deep lets say 4mm . Then we assumed that middle one must be bend, because you can compress it but not fully extend

What do you guys think that could cause bend middle intake valve??? Idle bike, low rpm like the guy said, or you think that he must have abused the bike in high rpm and cold machine???

If someone can clear me what could cause bend valve I appreciate it.

Thank you for replays

Best regards, Peter

[grayracer513]

When a valve bends, the stem is pulled farther down in the guide, so the clearance increases. When a valve is worn on the face, the stem moves farther up in the guide, and the clearance decreases. What you have is a worn valve.

If your friend honestly did not know this at the time of the sale, then in the U.S., the sale would be final. Under our practices, private sales of used vehicles are "as-is", meaning the bike is sold just the way it is, with all faults included, whether they are hidden or plainly visible. The seller can, if he wants, offer his own guaranty, but the law does not require it.

Only if it can be shown that this is something that the seller knew about, or should have known about, and deliberately avoided telling the buyer would the sale be illegal.

I have no idea how the laws work in your country, but here, it would be entirely up to your friend as to whether he will help the buyer in any way, unless he deceived the buyer in the first place.

[MX_Peter]

Thanks for quick replay

Has any one what to say. What could bend the valve or what usually bend the valve

thanks

[grayracer513]

A valve might be bent by having it stick open and getting hit by the piston. Also, something could have gone through the intake to foul the valve. It's also possible that the timing chain jumped, but that should have bent all of the intakes the same.

[MX_Peter]

No the timing is perfect. Only middle intake is bend, other two intake are fine. Something had to cause sticking of a valve and not extend fully. I'm just curious if is high rpm more likely to bend the valve or really low rpm when you almost fell engine make every stroke

[MX_Peter]

Any one please?

[grayracer513]

Low rpm won't bend a valve. Only the things I mentioned. High rpm won't hurt the valves either, unless there is something wrong. A weak or broken valve spring could be at fault, too.