No rev limiter on XT 600?

[D.T.]

I just revved the @#$# out of my XT600 to "get the carbon out" and try leaner jetting to get a bit more top end power. Well, it started sputtering after this. I got home and found low compression.

Just got the head off and my exhaust valves hit the piston. ? I just found one bent valve.

Where the valves hit the piston, they aren't even close to the cutouts in the Wiseco piston so I'm wondering if they even gave the right F'n piston. ?

Recommend a place I can get new valves? Do you think anything else should be changed? I may just leave the piston in. I don't want to put a lot of money into the old girl.

[timbuckets]

That sucks! ? I feel for you.

I think you can still get OEM valves from some places but its a common upgrade to use Yamaha Raptor/Grizzly 660 valves (I cannot remember which one) in this head. They are slightly larger OD on the exhaust side so you will have to get some grinding done. There are a few guys floating around here who have done this mod.

Did the valves do damage to the piston? If there are witness marks I would check that the wist pin and the big end bearing still feel okay. I would say the $20 in clips/gaskets would be worth the peace of mind, but thats just me.

Good luck and let us know how it goes.

[bergman501]

1st--is the eng stock? valve float caused this problem. valve reliefs are there when the valves are in time with the piston. when the valves float they get out of time and can come in contact with the piston. i've did this on a sb chevy and all 8 ex valves hit and did not blow up. on another race eng i wasn't so lucky. you can still get stock valves but are $$$ -- if going to do a valve job the grizzly 600 valves are cheaper and are 1mm bigger

[timbuckets]

Bergman - What springs did you use for these valves? If its stock springs, these caused the float. Won't the larger valves make that worse for him?

OR does the XT/TT just float went your way above the redline?

[bergman501]

sounds like he just over reved it. my eng has a whitebrothers cam (webcam) and their spring kit. also with a 11.1 piston. if org springs, i would replace them even with new stock springs. who ever does the valve job can ck spring pressure. no need to rev these old singles high. on my buddy's dragster he ck's the springs pressure after every few runs. of course this is on a 4.5 bore and 4.5 stroke eng (mopor 572 wedge-B1) running 8000 rpm. it could have been worse for DT.