Exhaust Valve dropping

mtbdrew · 11-02-2015, 11:38 AM

My son bought a 2002 GZ250 that according to odometer has 4600 miles on it. He added another 70 mile and the bike stopped running as he drove down the highway. Found the exhaust valves had broken off third the way up and destroyed the head assy and piston. We ordered a replace jug and head assy from China and got the bike up and running again but 32 miles later the bike stopped on the highway again. Took the cover off the head assy and found that one of the exhaust valves had pulled through the cotter and dropped getting hit my the piston and bent. The other valve was well on its way out of the cotters too.
Could these have just been bad cotters? Or is the bike running too lean get too hot and causing the valves to drop?
Everything is stock on the bike except he did replace the air filter with one that doesn't have the scoop attachment and is supposed to be "high flow". could this be causing the above problem by making the bike run too hot leading to these odd exhaust valve issues?

Thanks
Andrew

blaine · 11-02-2015, 04:21 PM

Not sure what is causing your problem but I highly doubt it is the air filter.I had a aftermarket filter in mine for 3 years & no problems.Sold her with 46000 or her.

mtbdrew · 11-02-2015, 04:40 PM

Quote:

Originally Posted by blaine

Not sure what is causing your problem but I highly doubt it is the air filter.I had a aftermarket filter in mine for 3 years & no problems.Sold her with 46000 or her.

Wouldn't have thought so myself but nothing else has been changed. If not for the first instance I would be willing to right the new case off as bad cotters metal being too soft which caused the ridge to give way and allow the valve to pull through.

The son swears he wasn't driving over 50 when it happened, it was raining this time so tend to believe him but he is 18 so anything is possible.

I tried to take the intake valves out to compare the cotters on them but they seem to be stuck so can release them with regular hand valve too. Will need to devise an alternative in order to remove them for inspection.

11-02-2015, 11:38 AM	#1
mtbdrew Junior Member Join Date: Oct 2015 Posts: 11	Exhaust Valve dropping My son bought a 2002 GZ250 that according to odometer has 4600 miles on it. He added another 70 mile and the bike stopped running as he drove down the highway. Found the exhaust valves had broken off third the way up and destroyed the head assy and piston. We ordered a replace jug and head assy from China and got the bike up and running again but 32 miles later the bike stopped on the highway again. Took the cover off the head assy and found that one of the exhaust valves had pulled through the cotter and dropped getting hit my the piston and bent. The other valve was well on its way out of the cotters too. Could these have just been bad cotters? Or is the bike running too lean get too hot and causing the valves to drop? Everything is stock on the bike except he did replace the air filter with one that doesn't have the scoop attachment and is supposed to be "high flow". could this be causing the above problem by making the bike run too hot leading to these odd exhaust valve issues? Thanks Andrew Login or Register to Remove Ads
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11-02-2015, 04:21 PM	#2
blaine Senior Member Join Date: Feb 2010 Location: P.E.I. Canada Posts: 3,784	Not sure what is causing your problem but I highly doubt it is the air filter.I had a aftermarket filter in mine for 3 years & no problems.Sold her with 46000 or her. __________________ If at first you do succeed, try not to look surprised.
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