[bigstick32]

So entering the motorway, sped up to 100km/hr and then this happened.

[gizzo]

Oh jeeezus thats faaarked mate. It won't buff out.
If that kind of thing happens to my bike the plan is to fit another engine. I think a DR or LS 650 will fit.
Welcome to the forum BTW.

[bigstick32]

thanks mate, yeah looks like I had the exhaust valve they made of pot metal or something. So engine mods have to come around earlier than my wallet expected. Hitchcocks here I come.  I also looked at the LS650 but the drive is on the other side, will it t work if I flip the wheel?

[gizzo]

I think that would work OK.   I'd just have to work out a new bracket to hang the brake caliper on the other side. 
Sounds like you're planning a rebuild:  are you saying the bottom end survived that catastrophe? That's impressive if it did.

[bigstick32]

rod was bent and some small damage in the case which doesn't look detrimental, I think the rod and the flywheels caused most of the piston grinding into a million pieces.
No pieces found on the gearbox side. Got replacement head, cylinder, piston and conrod from India and will get the performance valve kit and cams while I'm at it from Hitchcocks. Considering carb conversion too, and maybe manual decomp to give that true 60s feel.

[Arizoni]

Man!  That's too bad.

Most likely, the head of the exhaust valve broke off of the valve stem.

That has happened to a couple of the 500cc UCE's but usually it happens when the motorcycle is being ridden at high speeds (70-80 mph) for long distances at a time.

[gashousegorilla]

yeah looks like I had the exhaust valve they made of pot metal or something.

 Stainless actually.  And hold up quite well with a proper valve Job and decent valve springs I have found.    Wow .. that sucks.   I haven't seen one quite that obliterated yet  .. I'd be more inclined to take a look at your valve springs.  THEY are shyte !  And only good up the low 5000 rpm area , before valve control is lost.  Also how the geometry is, where your  rockers are contacting the valve tips....  The factory sometimes likes to set them up , where the rocker pad is running off the side of the valve tip at full lift.      Warped seats from excessive heat, stem to guide  clearance and etc....... 

   However , looking at the pictures of that pile of debris.   The crown of the piston ... if that is what I'm seeing there ?... does not look very damaged , as if a valve head was dancing around on top of the piston.  BUT... there are two big chunks taken out of your barrel at the bottom , as if the wrist pin slid out at bottom dead center.   And also scoring on the cylinder walls or either side of the Wrist pin.   Perhaps you lost one of the  C clips that retains the wrist pin... 

[bigstick32]

Some more pics of the catastrophe. The valve stem has a clean break, so valve broke, bounced around causing havoc, breaking the piston then the piston pieces were ground up by the rod and flywheels.

[gashousegorilla]

 Yup, I see it now.     If that's the exhaust side of the piston crown , it looks like the valve might have slammed into the top/side of it there, with how the crown looks bent upwards.

[bigstick32]

Last pic is exhaust valve, it snapped at the shoulder of the stem. The valve stem was still perfectly straight.

[Arizoni]

That's right where the weld joint is.

Like in many modern engines, the exhaust valve head is a hot gas resistant stainless steel and it is inertia welded to a hardenable steel valve stem.
Usually these welded valves will last a lifetime but sometimes the weld joint will fail, like it did in your engine.

If it does, all hell breaks out inside the combustion chamber. 

[gashousegorilla]

Last pic is exhaust valve, it snapped at the shoulder of the stem. The valve stem was still perfectly straight.

  I got ya now !   I evidently had dished PISTON on the brain, and not the dished valve head, when looking at your picture up top.      

[Bilgemaster]

I don't care that it's 3 years old. Barring outright abuse, any vehicle whose engine would dangerously self-destruct like that with just 6,000 km on the clock (less than 4,000 miles) should be fixed or replaced on the manufacturer's dime. They've had massive recalls for less. Am I seriously to understand that such valve failure is a common occurrence? If so, then that's outrageous and unconscionable.

[Adrian II]

I have heard of this happening to recent BMW flat twins.

A.

[ace.cafe]

I have seen it 3 times, in addition to what has been reported on this forum over the years.
All were early C5 models.
All dropped the exhaust valve head.

Two of them we repaired the heavy damage to the heads, and the customers rebuilt the bottom.
One of them is a warranty engine that I got during a clearance sale. It suffered this kind of damage during warranty, and they replaced it. I use it as a parts engine, and for reference.

The two we fixed had been ridden on the highway for all day in hot weather. I don't know the circumstances that killed the warranty engine I got.

Seeing you are from Australia, you should know that Australia is known for killing Bullets. Apparently there is a lot of hot weather and people get on the highways and drive at fairly high speed for long periods. The old iron barrel Bullets couldn't take this, and dropped like flies. The UCE does a little better.