Dropped 3 valves


15 replies to this topic
  • Strattos

Posted May 20, 2008 - 02:32 PM

#1

I've just totalled the top end of my '02 WR426 and am hoping to get the bottom of what caused the problem so I don't rebuild it and it just happens again.

I went for a ride last weekend and after about five minutes it started feeling a bit gutless. At first I thought the clutch might have been slipping but it was in spec. I turned around and went back to camp to investigate further when it locked up, coupled with a high pitch howling noise.

I've just pulled the head and cylinder off and its dropped three valves - all inlets and made an absolute mess of the head and piston. A piece of valve must have gone down the cylinder as well, as there are a couple of very small gouges in the bore.

In all three valves, the heads snapped off at roughly the same position.

The top end appears to have been getting enough oil as there was plenty up there.

In terms of background, the bike's done around 11,000 kms, has oil changes every five hours, a clean air filter every rider and valve clearance checks every 10 hours.

About three months ago I pulled the gearbox down after worn dogs on 5th gear caused it to keep slipping out. At the time I put new rings in it and checked the piston tolerances and it was all within spec. I adjusted the valves at the time as well, while I had the head off, as they were close to the minimum clearance. Apart from this it's been a bulletproof bike.

Since the rebuild I've done about 15 hours and three oil changes and it hasn't missed a beat.

I had done an oil change the day before going out on last weekend's ride.

Any suggestions as to what would cause this? And why the inlets only? After doing a search it doesn't appear to be a common problem.

  • KJ790

Posted May 20, 2008 - 02:43 PM

#2

Have you ever needed to shim the valves? are the piston, wrist pin, crank, and rod still intact as they should be? Are any of the valve stems bent? These questions may hold the key. There are many things that could have gone wrong. Chances are one valve failed and the head of it came up and hit the other two valves. It is also possible that the piston hit all three valves, but this would require the piston, wrist pin, crank, or rod to break.

  • Strattos

Posted May 20, 2008 - 03:56 PM

#3

Haven't needed to shim the valves before. We've still got to pull the bottom end down, but turning the crank, everything appears to be intact, as it turns over smoothly with no noises or anything. Will look into the other suggestions, thanks for reply.

  • SXP

Posted May 20, 2008 - 04:16 PM

#4

As it's all three intake valves, my guess is the intake cam was starved for oil at some point, causing the cam to seize, which caused the gear on the cam to spin, throwing your valve timing off. The valves then met the piston and grenaded.

  • Strattos

Posted May 20, 2008 - 04:20 PM

#5

Thanks SXP. But if that happened wouldn't there be signs of excess heat or something on the cam and where it sits in the head. As, from a quick look last night, they look undamaged.

  • off_road_4_me

Posted May 20, 2008 - 04:25 PM

#6

I would reallly really check the timing chain, it could have slipped.
oh yah, sorry to hear about your bike, its never fun to break your machine :thumbsup:

  • Strattos

Posted May 20, 2008 - 04:34 PM

#7

SXP and off_road, thanks for the input. If it did skip a tooth or so and changed the timing would that explain why it appeared to be underpowered? Or would it grenade the instant the timing went out?

  • KJ790

Posted May 20, 2008 - 04:37 PM

#8

If it skipped one tooth it may have kept running, but would be underpowered. Skipping a second tooth would make it blow up immediately. This is a good possibility for what could have happened. maybe a chain tensioner malfunction.

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  • Strattos

Posted May 20, 2008 - 04:50 PM

#9

Thanks guys. I'll have a good look over everything tonight and see what I find. Still waiting for the parts quote today. I'm guessing it's not going to be pretty.

  • SXP

Posted May 20, 2008 - 04:52 PM

#10

Here's a pic of a good intake cam with the 9 and 3 o'clock punch marks on the gear (on the other side) exactly in a horizontal line. The orientation of the outermost cam lobe should be as in the pic. If yours matches, then the gear has not slipped, and KJ's idea of a jumped cam chain would be a smart bet.

Posted Image

  • Frostbite

Posted May 20, 2008 - 06:00 PM

#11

Thanks guys. I'll have a good look over everything tonight and see what I find. Still waiting for the parts quote today. I'm guessing it's not going to be pretty.


Hey Strattos

Sorry to hear about your trouble. I snapped a valve last year and had to have a seat rebuilt and had all new valves and guides installed.
My engine was running fine, but snapped the valve during a high RPM run.
Because you snapped all 3 intakes, I'm inclined to think that your intake timing was off, or that it jumped. The fact that the bike seemed down on power may be an indication that the timing was off well before the destruction. Were you revving high when the valves broke?

Frosty

  • off_road_4_me

Posted May 20, 2008 - 06:09 PM

#12

SXP and off_road, thanks for the input. If it did skip a tooth or so and changed the timing would that explain why it appeared to be underpowered? Or would it grenade the instant the timing went out?


yes, one tooth the bike will still run, but will be gutless and run noisy, if it skips another tooth, boom.:thumbsup:

  • Strattos

Posted May 20, 2008 - 07:20 PM

#13

Hey Strattos

Sorry to hear about your trouble. I snapped a valve last year and had to have a seat rebuilt and had all new valves and guides installed.
My engine was running fine, but snapped the valve during a high RPM run.
Because you snapped all 3 intakes, I'm inclined to think that your intake timing was off, or that it jumped. The fact that the bike seemed down on power may be an indication that the timing was off well before the destruction. Were you revving high when the valves broke?

Frosty


Was revving reasonably high, no where near the rev limit though. Re the low power, it did more than 15 hours after the rebuild and was perfect, or I didn't notice it. It was only for the 10 or 15 minutes that my last ride lasted for that it felt under-powered. The only thing that i had done between the previous ride and the terminal one was an oil change and swapped air filters. Cam chain tensioner might have failed pretty much when I started the bike on the weekend.

  • rockieman

Posted May 20, 2008 - 08:11 PM

#14

I feel your pain, I suffered a similar fate a couple of years ago although I feel mine was not related to anything specific other then simple wear & tear. I had ~12,000 miles when one of my intake valves cut loose.
Here is a post I did at the time that outlines the cost.
http://www.thumperta...Cost to rebuild
Good luck!

  • Strattos

Posted May 20, 2008 - 08:21 PM

#15

I'll put up a couple of pics for comedy value (you've got to laugh at this point!) showing the results of the carnage that took place in my combustion chamber, when I figure out how to put them up.

  • matt4x4

Posted May 21, 2008 - 04:57 AM

#16

Carnage always sucks!
Sorry to hear about the valves - my first guess is the timing chain too, esp since you lost the 3 intakes all about the same way, same time.
You can probably pick up new valves for about 300, other incidentals like timing chain, piston kit etc for probably another 200, possibly only have to hone the cylinder depending on the depth of the scratches may need to nikasil it.
If you do it yourself, you probably still want to send the head out for getting the seats and valve guides replaced.




 
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