426 Carnage in Central Texas


16 replies to this topic
  • MNellis

Posted January 01, 2006 - 08:44 PM

#1

The trail riding gods were angry today my friends......

Please recall that about 6 months ago I had a massive failure where my piston at itself up, plugging the oil screens and wobbling so bad that it touched the intake valves, bending them all.

If you missed it you can read about it in this thread. Then read the latest story.

http://www.thumperta...26&parentpage=2


I just got my Rekluse clutch installed and looked forward to testing it out on my unsuspecting 2 stroke buddy and his YZ250. We were riding on some leased property and did on lap about 5 miles long. The Rekluse clutch is phenomenal!! I didn't fall once and was able to stay with my buddy although, in his defense, he was breaking in a new top end on his bike so he was taking it pretty easy.

Things went well as we finished the first lap and headed back to the truck. Just as I was pulling up to park I heard a very loud grinding noise and the motor just stopped. Everyone around me heard it and they all came over asking, "what was that?".

"I dunno", says I. "I just put this new clutch in so maybe something broke", I continued.

My wife grabbed the tools and I pointed to the clutch cover and she went to work while I got a quick drink. We popped the bike on its side and took the clutch apart but couldn't find anything wrong. I didn't think we would since I thought the noise sounded like a cam chain. Since the motor was froze solid it was time to load the bike up and go home to assess the true damage.

Back in the driveway we popped the bike on its other side and I decided to take a look at the bottom of the cam chain first to see if there was anything obviously wrong there. I didn't think I'd find much there either but it was an easy check before pulling the valve cover off.

My chief mechanic went to work again.

Posted Image

Not seeing anything obvious we had no choice but to tear into the top end. Immediately after pulling the valve cover off we saw the source of the noise. At first glance it appeared that the shim bucket had shattered as there were pieces all over the place.

Posted Image


We took the NEW exhaust cam out and found even more pieces and parts missing.

Posted Image


We started pulling pieces out with a magnet.


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This is what we pulled out. You can see the shim all buggered up there along with the retainer clip and what left of the bucket. As you can see in this picture, the lifter bore is all chewed up as well and I'm starting to get real worried and see nothing but $$$$$ in my future. Damn, I just spent $1300 putting this motor back together earlier this year (about 15 hours on the bike at most since the rebuild)


Posted Image



At this point I figured I broke a NEW exhaust valve and that's what caused the problem. As we pulled the head off and looked in the bore we saw the head of the valve embedded in the top of the piston along with the rest of the pieces and parts of exhaust valve train components.

Posted Image

It was at this time that I turned the head over and saw the serious damage. Even more surprising was the fact that the exhaust valve was intact but it was the intake valve head that had popped off! Unbelievable. The intake valves were all brand new as well. In addition to the lifter bores being shot the head is pretty bunged up and the valve seat is shot. In my opinion the head is going to need to be replaced.


Posted Image


Surprisingly, the piston bore is in great condition. With so little time on the rebuild I figure I could probably just buy a piston and reuse the rings but I'll probably hone the cylinder and get new rings anyway but reuse the piston pin that was new at the rebuild. I will replace the head along with all new valves and seals. I will probably reuse the valve springs and remaining keeps and lifters. The new 450 exhaust cam lob was pretty chewed up so that will have to be replaced as well.

I guess the good thing is that I found out I LOVE the Rekluse clutch and that it didn't strand me on the trail 5 miles out or so. :applause: Keep in mind, this damage was cause with the bike almost at idle as I was coasting to a stop and with the Rekluse clutch this is just over idle.

  • MNellis

Posted January 01, 2006 - 08:47 PM

#2

Sorry for the picture links. I don't know why the [img] tag won't work. :applause:

  • FZ1426

Posted January 01, 2006 - 09:11 PM

#3

I think I would have a talk with my "chief mechanic".

  • flats00

Posted January 01, 2006 - 10:32 PM

#4

Unreal !!!! Don't fire the machanic though. Any one with a smile that big after such a catastrofy must love what they do.

  • kawirider

Posted January 01, 2006 - 11:19 PM

#5

Did you rebuild it yourself earlier this year?? If you did, I would recomend taking it to a professional that offers a gurantee this time. So that if this crap happens again, you will not be responsible. Sorry to hear about your bike.

  • SureBlue

Posted January 02, 2006 - 12:02 AM

#6

Did you rebuild it yourself earlier this year?? If you did, I would recomend taking it to a professional that offers a gurantee this time. So that if this crap happens again, you will not be responsible. Sorry to hear about your bike.

There is not a mech that offers guarantee of any kind on a racing bike rebuild.
Everybody knows anything can blow up anytime. Skilled mechanics earn their reputation and you just got to find the skilled ones to do the job.

  • Satch0922

Posted January 02, 2006 - 05:59 AM

#7

if appears from the pictures that the valves (more than one) were hitting the piston. The valves were shimmed properly at rebuild? Did the cams jump time? What are the pieces in the top of the head.....the valve bucket? If the bucket came apart and lodged under the cam then it would have pushed the valve down too far causing it to hit the pistion.

That is what you need to figure out before you rebuild it. If you don't pin point the cause you run the risk of having it happen all over again.

  • MNellis

Posted January 02, 2006 - 06:23 AM

#8

..... I would recomend taking it to a professional that offers a gurantee this time. So that if this crap happens again, you will not be responsible.


As somone else said, there is not a Yamaha shop in the country that is going to warranty a rebuild for more than a day on a race bike motor. To many variables once it leaves the shop. The local "authorized" Yamaha dealer couldn't even sell me valve shims without ordering them.

if appears from the pictures that the valves (more than one) were hitting the piston. The valves were shimmed properly at rebuild? Did the cams jump time? What are the pieces in the top of the head.....the valve bucket? If the bucket came apart and lodged under the cam then it would have pushed the valve down too far causing it to hit the pistion.

That is what you need to figure out before you rebuild it. If you don't pin point the cause you run the risk of having it happen all over again.


The pictures can be deceiving. All the carnage you see on the exhaust is a result of the intake valve breaking, getting under the exhaust valve with the resulting problems. So why did the intake valve break? Dunno. The valve adjustments were fine. They were fine when the motor went together and they were fine after the first few hours of riding. The bike as been running great since the rebuild. Starts first kick, didn't backfire, didn't make any noise....go figure.

Did the timing chain jump a tooth? That would just be speculation since the
engine couldn't be rotated to check the timing. At this point all I can do replace the broken parts and ensure it's all put back together properly.

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  • Satch0922

Posted January 02, 2006 - 06:27 AM

#9

MNellis,

I am just having a difficult time visualizing how the pieces got into the top of the head.....

  • MNellis

Posted January 02, 2006 - 07:09 AM

#10

MNellis,

I am just having a difficult time visualizing how the pieces got into the top of the head.....


They didn't "get there", they were already there. They just shattered. The pictures of the pieces being pulled out with the magnet were the exhaust lifter, retainer etc. but the valve itself is intact. The intake valve head, on the other hand, was broken off inside the bore and lodged in the piston along with the bits and pieces from the exhaust side that fell down when the exhaust valve was lodged open.

The initial failure was with the intake valve although none of the lifter, retainers, spring or anything else appears damaged on the intake side.

In my opinion at this point, the intake valve broke and caused the rest of the problems that are visible. The question remains, "why did the intake valve break?".

  • Satch0922

Posted January 02, 2006 - 07:15 AM

#11

ok...I am hard headed.....how do you know the intake valve was the initial failure? Why would that cause the exhaust valve bucket to shatter? I can see if you dropped and intake valve that it would possibly break one of exhaust valves....but cause the exhaust valve bucket to shatter?

Maybe I am missing something but I think the bucket broke (due to wear ??) and then got a piece in between the intake cam lobe and valve bucket and caused the intake valve to hit the piston??


Just speculation of course but it would explain the carnage and multiple issues goin on there.

  • sirthumpalot

Posted January 02, 2006 - 07:34 AM

#12

I'm not going to guess what failed first, but here are some tips that might help in the future:

Were any of the valves missing the retaining clips? Just curious.

When you reassemble, put some very small pieces of clay on the piston where the valves will get close. Assemble the motor (including cams and timing chain) and spin it slowly by hand. Pop the head off and take a look at the clay. This will tell you if you have a valve getting too close to (hitting) the piston. If it's barely touching the piston then you may not notice while spinning the motor by hand, but at high RPM it might be enough to weaken and eventually break the valve.

Be sure to use new valve springs, or in the least make sure they are within spec. Weak valve springs won't be able to close the valve fast enough at high RPM and they may possibly be smacked by the piston. Even a light tap that might not cause immediate failure could over time weaken the valve and cause it to fail at a later time. While it broke at idle, the actual event that weakened the valve likely occurred at some other time.

Finally there is a head shop that some people here have used to fix head problems and they seem to be able to work small miracles. I don't remember the name, but search the threads and maybe they can save you the cost of a new head?

Hope this helps and best of luck with the rebuild!

  • fishnbc

Posted January 02, 2006 - 09:27 AM

#13

Were the new valves Yamaha or aftermarket. If the springs are original I wouldn't hesitate to run all new as well as valves, keepers, retainers, etc.

  • MNellis

Posted January 02, 2006 - 02:34 PM

#14

Were any of the valves missing the retaining clips? Just curious.

When you reassemble, put some very small pieces of clay on the piston where the valves will get close. Assemble the motor (including cams and timing chain) and spin it slowly by hand. Pop the head off and take a look at the clay. This will tell you if you have a valve getting too close to (hitting) the piston. If it's barely touching the piston then you may not notice while spinning the motor by hand, but at high RPM it might be enough to weaken and eventually break the valve.


Only the exhaust lifter was damaged and I found both clips so I'm assuming they were in place.

We use the "clay on the piston" technique when we blueprint our roadrace motors but given that the piston and cams were stock Yamaha units and there was no "decking" machine work done I didn't feel it was necessary during the previoius rebuild. Your point is well taken and I may do that after this rebuild as well.

I've also seen threads on the shop that does head work and they might be worth calling up to get a quote, but the damage to the valve pocket and head surface is pretty significant.

  • MNellis

Posted January 02, 2006 - 02:36 PM

#15

ok...I am hard headed.....how do you know the intake valve was the initial failure? Why would that cause the exhaust valve bucket to shatter? I can see if you dropped and intake valve that it would possibly break one of exhaust valves....but cause the exhaust valve bucket to shatter?

Maybe I am missing something but I think the bucket broke (due to wear ??) and then got a piece in between the intake cam lobe and valve bucket and caused the intake valve to hit the piston??


That's another way to look at it but there was no small pieces of shrapnel on the intake cam area at all so I don't think anything got between the intake cam lobe and the lifter. On the other hand, if the intake valve broke then got stuck so the exhaust couldn't open fully then the cam stress on the lifter could cause what we see here. Who knows? It's tough to tell.

Were any of the valves missing the retaining clips? Just curious.

When you reassemble, put some very small pieces of clay on the piston where the valves will get close. Assemble the motor (including cams and timing chain) and spin it slowly by hand. Pop the head off and take a look at the clay. This will tell you if you have a valve getting too close to (hitting) the piston. If it's barely touching the piston then you may not notice while spinning the motor by hand, but at high RPM it might be enough to weaken and eventually break the valve.


Only the exhaust lifter was damaged and I found both clips so I'm assuming they were in place.

We use the "clay on the piston" technique when we blueprint our roadrace motors but given that the piston and cams were stock Yamaha units and there was no "decking" machine work done I didn't feel it was necessary during the previoius rebuild. Your point is well taken and I may do that after this rebuild as well.

I've also seen threads on the shop that does head work and they might be worth calling up to get a quote, but the damage to the valve pocket and head surface is pretty significant.

  • Satch0922

Posted January 02, 2006 - 05:14 PM

#16

Keep us posted on what you find out....I am really curious. I put a lot of time on a 426 and have a friend who rides WFO (Kirtwell :bonk: ) who put 400+ hrs on one without a rebuild so this is a shock to my world! LOL :applause:

  • 426boy

Posted January 02, 2006 - 08:31 PM

#17

ahh that really sucks





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