What causes damage to the top of a valve??

Started the bike to warm it up for an oil change and heard a loud ticking coming from the left side of the bike. The noise kept tempo with the motor so I staryed to pull stuff apart. Oil was clean, no bearing material, spark plugs were clean, valve clearances were ok except one. I just adjusted them two race weekends ago. #1 cyl #1ex valve was WAY loose, measured .305mm. Took the cams out and saw the valve is sitting low and the top is mushroomed. Why the heck would cause this?? The schim was sitting in the middle of the bucket as it should. Here's a pic of the top of the valve, one on the left. Bike is a 2011 zx10.

 

Not sure, but better put some Carrillo valves in there

 

Livengood.

 

Few things, keepers wearing out, retainer wearing out and buckets hitting retainers (marks on both of them).

 

So I guess it's safer to say I should replace all the retainers and keepers? If it's happened to one the others probably aren't far behind.

 

To much clearance will let the cam beat on the buckets/shims. At that point the top of the valve is the weakest point and tends to do that. In all our big car stuff our ti valves have hardened tips for that reason.

 

I don't think retainers or keepers are the cause. And I also think changing them will do nothing. I'd say they are fine.

 

I'm trying to figure out what caused the clearance to get so big. How does a valve go from the larger side of the spec to $5 hooker in two race weekends? The motor has 6000km on it now, 4000km of racing which is a good season down south I would think. Up here we get 7-10 races a year.

 

After a closer look it seems as if the tips of the valves are starting to wear. There's some pitting and you can see that some of the coating is starting to wear off. Time for new valves I guess.

Maybe that one valve took a beating in the last race and when it was hot the clearance was close enough that there was no tick??

 

I would tend to agree with that and say you caught it before it took the remainder of the motor with it.

 

4000 km race time? What is that ? 2200 miles? I believe the answer to the problem is that you didn't tear in to it sooner.
All I can say is when I was serious about racing, My shit got rebuilt every year (money permitting). The rich boys would rip their stuff down 2-3 times a year.

 

Bottom end was redone at the beginning of last year so it's got around 1000-1500km on it. Top end was worked on, valves set at the beginning of the year. I planned on doing the valves and bottom end again at the end of this season which started two weeks ago and is over mid August. Motor is pretty much stock so I thought it would last a little longer.

Ah well, thank F it wasn't worse.

 

Yeah, Really. Dodged a bullet on that one.

 

And the one spring retainer on the damaged valve looks like it has some wear. Order up one extra retainer to go with the 16 valves. OUCH!

 

Valves and springs are wear items. Might as well get 16 more springs to ease your mind. And a fresh valve job too.

 

All valves, springs, retainers, springs etc are being replaced. Hopefully the valve job from last season is still in good shape.

 

Did whomever did the valve job last season "tip" the valves? By that I know some shops (not one I would want to use) will grind the tip of the valve by the amount they cut the valve seat in order to keep the same shims usable assuming valve clearances were good before they pulled it apart. Saves them labor on reassembly but can screw you as they just removed some of the surface hardening in that area.

 

I'm going to say no. He's a reputable builder and you can see on the tips of the valves that the coating looks untouched. I could be totally wrong but I very highly doubt it.

 

Understand, just wanted to toss that out. I had a head done by NPS a couple of years ago and they did it to that head, just one of the reasons I won't use them again.

 

Re-tipping valves is still a fairly common car thing, 350 chevy's and other heavy shit. Ti valves are not used so no issues. Lot's of machine shops don't spend enough time work on our "small" stuff to even think about it. I showed a picture of the insides of an NR750 years ago to a machinist. I still don't think he every really figured out what was really going on. He kept asking, "How many valves in it....That just doesn't look right...."