Bad, bad sounds...broken valve

Please tell me how this happens when an engine is timed perfectly...

 

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Luckily the bore still looks ok...

 

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I just bought the bike about 8 months ago and it hasn't given me any issues. The PO adjusted the valves too tight when I bought it, so I readjusted them properly. One valve had a little valve tap, but nothing major. I was going to fix it soon. So I had just gone for a short road ride (road legal), got on the gas to pull a brief wheelie and settled to a cruising speed of about 45mph. Not 10 seconds later I hear a sound like when you try to start an already started car (gears grinding together) with an immediate loss of power. I knew something major happened so I immediately pulled in the clutch (within 1 second) and coasted to a stop. I pushed the kickstarter with my hand and it wouldn't budge.

 

I had assumed my camchain broke or something since I know that's a weak spot with these. Long story short, I took it apart the next day and I found the above pictures.

 

So my question is why? The valve that snapped looks like it was a clean break, not from a piston hitting it. It looks more like the spring pulled the valve stem away from the valve and just popped it off. Has anyone seen this happen before?

 

My next question, is it impossible to repair the head, or am I better off buying a new-used head off ebay? Those things are surprisingly pricey.

I'm not sure how old your bike is but I have heard of a few titanium valves letting go. I think there were a few in 08 that supposedly had bad valves.

I decided to run the stainless steel valves and heavier springs.

You can also buy American made titanium valves.

Let a machine shop that does valves look at your head to see if it can be fixed.

Edited by stevethe

That's the odd thing. They are certainly to heavy to be titanium.

And it's a 99 Wr400

I'm not sure if the 99 had ti valves. However she does have couple of years on her.

The timing chain tensioner is probably worn out, the the ex cam skipped a tooth or two....

Or.... the valves were worn out, the PO shimmed to compensate and finally, the valve failed. See it all the time, sadly too often on bikes a guy just got that 'had the valves just shimmed by the PO'.

 

All three intake valves have hit the piston, only one catastrophically.

 

The head is repairable. A new seat, all new valves, springs, retainers. You will also need a new piston, and crank as well as some other odds and ends.

The valves were contacting the piston for a while.  I vote excessively worn timing chain or jumped a tooth.  Valves receding into the head would not cause that.

It could also be some wear in the bottom end; con rod, crank, wrist pin, even an excessively work piton/barrel causing it to rock in the bore.

Edited by bikedude987

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