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Owlmeat

01 426 Suggestions on Broke Top End? (*big pics)

12 posts in this topic

Hi everyone! Please forgive my long first post here. Typically Id hang around a forum for awhile before dropping an info bomb like this one. This is simply one of the most informative sites I have ever seen. From ghosting this place for 3 days, I’ve already accumulated knowledge that would take months on my own. (I am a 2-stroke convert. I have no problem with total rebuilds, but I need to bring myself up to speed on 4-stroke troubleshooting and tuning). I plan on hanging around for a long time, and maybe contributing someday... but for now:

I need some advice on an 01 YZ426 with head damage I recently purchased. Here is a list of what I do and don’t know: I have no idea as to how the bike was maintained. This includes oil changes, valve adjustments, hours on the bike, type of riding, weight of rider. I think the bike was woods rode due to setup. I know nothing other that the condition of the bike. It is in poor condition, but it is due to neglect, rather than abuse. The rear sprocket is whooped out farther than I thought possible. I have to assume that this bike was neglected on filter and oil as well. However, the original cross hatch is still evident in the cylinder. I haven’t had time to mic it yet, but I certainly will.

http://www.owlmeat.com/426.htm

Ive posted a bunch of pictures on my website that may help explain what happened to the top end. Unfortunately I bought the bike after it was torn down. It appears that the valves were either floated, or maybe there was cam / chain / tensioner issues. Maybe the sprocket spun? In any event, the top of the piston contacted the failed valve 2 or 3 times violently, then maybe a hundred times after the damage was done. As you can see, only 3 valves look like they were damaged. Two bent, one broke. When I wiggle the c rod vertically, I don’t feel any play, and oddly enough it still feels smooth when rotated. I plan on replacing big and small bearing, as well as left and right, and getting the crank miced for wobble, just in case. The valve springs appear to be in good condition, but Ill replace those too, since they’ll be the last “old” thing left in the top end.

Here are my questions to the pros out there:

1) What do you think happened to cause the initial contact?

2) What do you think is up with the small head damage that is on the valve side?

3) What are your gut-feeling chances that the crank is straight?

4) I don’t plan on it, but would you reuse the other two valves if they were straight?

5) I plan on trying to rebuild the head via Engine Dynamics or someone similar. If I stay with my current head, what years and models can I get valves out of? (I understand 2000 had steel, and I think 2003-5 are shorter, but what about a 250 model? Will those valves drop in?

6) Does anyone have a good reseller contact for Del West or blackdiamond / Kibblewhite valves?

7) If I can find the whole assembly (valves and all), will a 2005 450 head drop on my 426? (The entire low head design) This will probably need 05 chain and guides I guess.

8) Does anyone suggest machinists other than Engine Dynamics?

9) Is there anything I’m overlooking?

10) Got any extra parts? HAHA!

Thanks to everyone!

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At first glance

It looks like something was sucked into the intack and chewed up your guts :naughty:

Those divit holes were not caused by anthing the valves did for sure. All you valves are intact.

Something definetly went down the trhought of the beast and did al that.

I would guess the guy who took it apart and put it back together may have droped something down the in take

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Thanks JL, that may be.

This is my theory, feel free to load up on ammo and blaze away at it... One of the valves is broke. (see the 3rd pic down on my page) So, if the valve head broke off, it would release the tension on the valve shaft, the keepers on top of the spring cap would come unseated, fall off, and allow the shaft to drop down into the cylinder area. Then the valve shaft would get whacked by the piston, breaking the valve guide at the weakest point.

Does that sound plausible?

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That's how I would call it. You may want to send these photos to Engine Dynamics in Ca. I have seen ED fix issues much worse than this. E-mail them and paste you link and ask for an estimate.

Can't hurt.

Bonzai :naughty:

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Sorry I missed that broken Valve :naughty:

I agree with Yamakaze as well then, Cant vouch for Engine Dynamics, but if Yamakaze says they is good then thats good enough for me.

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Can you tell us if the cam was stock? Or show us a picture? That might help.

You might want to get new shims and buckets too. I would 86 the old valves for sure. This might be good for a 5angle cut valve job :naughty:

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Here are my questions to the pros out there:

1) What do you think happened to cause the initial contact?

2) What do you think is up with the small head damage that is on the valve side?

3) What are your gut-feeling chances that the crank is straight?

4) I don’t plan on it, but would you reuse the other two valves if they were straight?

5) I plan on trying to rebuild the head via Engine Dynamics or someone similar. If I stay with my current head, what years and models can I get valves out of? (I understand 2000 had steel, and I think 2003-5 are shorter, but what about a 250 model? Will those valves drop in?

6) Does anyone have a good reseller contact for Del West or blackdiamond / Kibblewhite valves?

7) If I can find the whole assembly (valves and all), will a 2005 450 head drop on my 426? (The entire low head design) This will probably need 05 chain and guides I guess.

8) Does anyone suggest machinists other than Engine Dynamics?

9) Is there anything I’m overlooking?

10) Got any extra parts? HAHA!

Thanks to everyone!

1) Cam timing. Check the condition of the crank sprocket and the tensioner. Also look for an indication that the intake cam may have seized. Valve float is not likely, as all three hit the piston. I'm very curious about the gash adjacent to the left intake valve cam follower bore. What caused that?

2) Not sure what you mean, but like Yamikaze said, EDCO can fix it. It's from the valve head bouncing around. You're very lucky it wasn't much worse. It must have done this at a low speed and been stopped immediately. :naughty:

3) It's probably straight, but there's a very good chance that the crank pin and/or rod has dents in it from the rollers due to the impact. Better do a rod kit.

4) Don't think so.

6) Thumper Talk Store

7) I don't know, but I doubt it.

8) Not for this job.

10) Sorry :naughty:

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Smoke,

One of my buckets is missing, I agree Ill be replacing them as well. Ill take a few pictures of the cam and post them by 7pm tonight.

Gray,

The "gash" you are describing in (1) is the same thing I’m trying to describe in my (2). I cant explain it. Since I’m missing 1 bucket, I’m thinking that maybe it failed, broke apart, and got caught between the spring the spring bore? I don’t know, sounds crazy though.

Thanks for everyone's help! :naughty:

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Smoke,

One of my buckets is missing, I agree Ill be replacing them as well. Ill take a few pictures of the cam and post them by 7pm tonight.

Gray,

The "gash" you are describing in (1) is the same thing I’m trying to describe in my (2). I cant explain it. Since I’m missing 1 bucket, I’m thinking that maybe it failed, broke apart, and got caught between the spring the spring bore? I don’t know, sounds crazy though.

Thanks for everyone's help! :naughty:

The bucket is probably in pieces in the bottom. Most likely went down past the cam chain. It was probably broken by the same impact that broke the valve guide, that is, I think it was a victim, and not one of the causes. I'll stick with my response to #1. Be sure you find the shim, too.

Good Luck.

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The bucket is probably in pieces in the bottom. Most likely went down past the cam chain. It was probably broken by the same impact that broke the valve guide, that is, I think it was a victim, and not one of the causes. I'll stick with my response to #1. Be sure you find the shim, too.

Good Luck.

I will be willing to bet that the reason you are missing the bucket is due to dude having to dig it out of the head....Hence what looks to be pry marks around that bucket.....

I would agree with the jump time someone was getting at.... Bet the chain streched or the tentioner failed..... :naughty:

I don't thinkt the 03-05 head will work with out some modifications...

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