Posted November 04, 2003 - 06:35 PM
Posted November 04, 2003 - 10:02 PM
I've got a 02 yz426 and can't figure out why the head self destructed.
Are you saying the piston didn't have anything to do with it?
Heads do destruct, but typically they have help from the piston. At the very least a camshaft steps up to the plate...
Posted November 05, 2003 - 06:20 AM
Posted November 05, 2003 - 02:47 PM
Posted November 06, 2003 - 11:10 AM
Posted November 06, 2003 - 07:07 PM
Posted November 06, 2003 - 07:52 PM
Been there, a year ago my 01 wr 426 went ka-boom. The center valve keeper let go and sucked in the valve. Wasted head, piston and three valves. Bore was fine. I rebuilt with a 13.5 to 1 piston tit.YZ valves and a new head with all new internals. And one new intake cam. Total bill...$1075.00 and I did all of the work. The bike now makes 54.6 ponies on dyno useing a 14/50 gear on 91 pump gas. Jetting was simple to dial in with that pistion, only one problem, the front tire will not stay on the ground in third. Thinking of using tractor weights to hold it down. Good luck with the rebuild dude!!
Whoa! Got to love retail. Just remember most of the OEM parts can be marked up 50% from cost, so shop around. Also it helps to know someone that works at a shop or work at one like myself!
Posted November 07, 2003 - 10:21 AM
I rebuilt with a 13.5 to 1 piston tit.YZ valves and a new head with all new internals.
My '02 had an intake valve break. Yep, the titanium valve broke off at the base of the stem and wrecked the head and piston, and bent all the other valves. 1600 miles, valve clearance was properly ajdusted.
Anyway, I am interested in your repair. I didn't know the WR and YZ valves were different, can you tell me what is different and why you chose YZ? Are the springs different also? Who makes the 13.5:1 piston and where do I get it? As long as I need to spend lot's of $$$$, I may as well get more performance too.
Was your rod bent? From what I can see, mine looks OK. Does anyone know how I can check to be sure the rod is not bent? I would hate to split the case unnecessarily, but on the other hand I certainly don't want to put it all back together with a bent rod?
Thanks in advance,
Posted November 08, 2003 - 12:03 PM
99.99% of the destroyed heads I have examined over the years have been traced to OTHER problems.
Something touched the valve head and it broke.
Valves, specifically those of the one piece variety, have a much higher chance of survival than those of the fused variety in situations of contact but they will fail under constant contact.
Your are looking at an effect not the cause.
Sorry to pontificate, this is just my experience.
Posted November 11, 2003 - 09:05 PM
Posted November 12, 2003 - 12:31 PM
Hope this info helps. BTW the dyno # are using WR timing and stock needle with air box top off and grey wire pulled. I may switch to YZ timing and needle this spring just to un-leash a rocket for alittle while to [@#$%&!] spank this Husky 610 I've been riding with.
Posted November 12, 2003 - 02:18 PM
The wrist pin size changed in '01 to 19mm from 18mm.