bad head

11 replies to this topic
  • J-Dawg

Posted June 18, 2002 - 06:28 AM


has anyone broke an exhaust valve before and what do you think caused it ? Possibly is someone wanting to get rid of a head ? When my valve broke it screwed up my valve bucket guide.

  • YZ400Court

Posted June 18, 2002 - 08:26 AM


I broke ex valves. It also shattered the valve buckets, and the cams drove the bucket parts into the soft aluminum head. It took a while, but I finally found someone here on TT selling a used head. I believe nine was caused by overrev when I missed shifts during a race. I also found a bent shift fork (cause of missed shifts).

  • Shawn_Mc

Posted June 18, 2002 - 01:35 PM


Floating exhaust valves is what causes contact between valves and heads. The intakes dont get smacked because they are closed when the piston comes up, but the exhaust valve is hanging open, and when floating because of over rev or weak springs, some times gets tagged and tagged good. If your a racer that has a deep relationship with your rev limiter, ya know Im talkin about, the kind of relationship with lots and lots of contact, you should change out your valve springs at least once a season, maybe twice depending on how much you race.

  • Bill

Posted June 18, 2002 - 02:10 PM


As a moderator............... I have to say this title caught my eye :) :D

Bill :D

  • Guest_mxrider426_*

Posted June 18, 2002 - 02:15 PM


What do you mean by floating?

  • Fastest1

Posted June 18, 2002 - 07:45 PM


The speed at which the valves are traveling allows them to lose contact with the cam momentarily. So therefore it is referred to as float.

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  • yamaha.dude

Posted June 18, 2002 - 10:56 PM


Valve float is what happens when the valve springs are not able to close the valves hard or fast enough, and with the exhaust valves, they are open when the piston comes back up and wham - a collision at about 25m per second or 90kmh... not sure of the mass of the piston, but that is a lot of force...

As for a having a bad head, well, don't drink so much the night before... :) :D


[ June 19, 2002: Message edited by: yamaha.dude ]

  • J-Dawg

Posted June 19, 2002 - 04:18 AM


When I broke the valve I was doing a wheelie up a hill at Pismo , so I think it could have just been a weak spring . Luckily it did not happen earlier when I was jumping a 90 foot double or I could have been on my head . On that same double I overjumped and broke my Shoei on my bars and pushed my goggles up and scraped up my foreherad . You know what they say , go big , crash big !

  • Fryboy

Posted June 20, 2002 - 06:06 AM


Quote: Bill As a moderator............... I have to say this title caught my eye

I was gonna add.... is there such a thing?

  • Boit

Posted June 21, 2002 - 02:30 AM


Bill; A little serendipity your way came?

  • Mark_Cantrell

Posted June 21, 2002 - 02:49 AM



I don't think so but I keep on looking.


  • Mark_UK

Posted June 21, 2002 - 03:05 AM



(confused look)

thats like saying ''BAD RIDE''

OH,,,errrrr,,,,, hang on,,,,,,,,,

[ June 21, 2002: Message edited by: Mark_UK ]

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