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Another top end gone!

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I have been punished for my feelings of superiority. I've been so proud that my '02 YZ (which had some race time on it when I bought it) valve clearance has been in spec over the two years plus I've had it. The clearance on the ex was even in spec when I installed the "03 cam! I had just completed checking valve clearance, oil change, etc. and went to ride at local practice track. One 20 min plus session all great. Second session the same. A few laps into third session - KABOOM! I was concerned that I might have over looked something cam chain, whatever. What I found was left intake valve head broken off, punctured the piston crown, and trashed the cylinder head.

1. Does Yamaha or anyone sell head assemblies comeplete with valves and cams? If so, I'll have a good '03 ex cam for sale!

2. Any reason why the '05 head won't work?

3. Is there a way to ensure the rod/bottom end is intact and clean without splitting cases?

4. Since the clearance was not closing, was it just too much time on machine? I probably put 150+ hrs on it while I had it.

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the bottom end is toast.

you need a new crank assembly.

it was time for that valve to go. sorry to hear about this.

as far as i know, yamaha does NOT sell a complete head.

had you ever changed the valve springs?

sorry to hear about this.

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Hadn't changed springs. Thought it was all ok if the valve clearance wasn't closing.

Guess I'll be splitting cases for the first time since the 70's. (I took a 20 year break. I'm 61) I had just listed my 250 & 426 for sale intending to get an "05 250F for the new suspension. Maybe I can still stretch the fun budget. Anyone want a "project bike? Or may be its time for a 262 kit.

Anyway, is the '05 head really different in porting and/or combustion chamber like the 450? If so, do I get the '05?

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I'll plan the '05 head. I have the decomp cam. I am guessing the higher velocity gives most benefit at low/mid range rpm? I don't push the rev limiter very often.

Looks like parts at retail are four figures plus before I even figure the bottom end.

Maybe Honda and Kawazuki are on to something with the clearance closing to give warning? Valves and springs would have been cheap!

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You might want to consider parting the bike out and getting the 05 you have your eye on. I parted out an 02 and did pretty well. If you do decide to fix it replace all the bearings while you have it apart, the sudden stop when the bike siezed can do bad things to bearings.

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Was the valve spring broken on the one that went into the piston? I'm just going to hazard the guess that the piston broke the valve after the spring failed and dropped it.

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A few laps into third session - KABOOM! .... Since the clearance was not closing, was it just too much time on machine?

All brand loyalty aside, that sucks. As an owner of Red titanium valves, a catastrophic failure like that without warning itsn't good news for anyone. I was under the impression that Ti valves usually failed only after several reshimming sessions. Although I hope grayracer513 is right, does Yamaha have a recommended replacement schedule for the valves?

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Valve spring is entact. The damage outside the combustion chamber is the center valve bucket fractured, apparently when the piston forced the left valve head against the center valve head as the cam was trying to open the center valve. The center valve is entact except for the interference marks.

The value of the bike as a "part out" isn't all that much less than an '02 that runs! I already have someone interested in the bike "as is" so I'm dealing for my "05!

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Just pulled out the broken stem. Clean, nearly square break, right where the taper to the head starts.

Guess I don't push the rev limiter enough to have the clearance close up before tripling the recomended replacement time.

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The square break is a result of the two piece design of the Titanium valves.

This is why some folks opt for Kibblewhite Stainless valves. They are a one piece design.

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I can understand putting ss valves in the lower rpm 450's, but the added stress of stronger springs to close heavier valves on a 13,000 rpm engine surely add significant continuing stress issues. The engineers didn't go to titanium for bling or promotion. (except on the later 426's)

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The square break is a result of the two piece design of the Titanium valves.

This is why some folks opt for Kibblewhite Stainless valves. They are a one piece design.

I believe the Del West titanium valves are one-piece also.

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