Piston Hole Kz1000LTD 1982

Allright,

First things first... happy new year to y´all.

Down to business. I recently started dissassembly of a 1982 Kz1000LTD, which I plan to rebuild to stock. Originally I bought it with an engine failure, which I assumed was valve oil seals, but on opening the engine, and planning to just take the head off, I noticed a large gaping hole in piston #2. Cams look pristine. 

I am attaching some pics for the experts to assess. I´m all in to getting a new set of pistons and rebuild everything up. My doubts and questions are:

1.- I have no idea what caused the hole, but could the hole have damaged something downwards (crank, rods, etc.)
2.- Would the piston trash have been evacuated through the exhaust? The oil had no sign of metal filings or bits
3.- Cylinders seem not to be damaged. I´m looking at new oversized pistons and a cylinder boring. Question: How do I know if pistons are original size? (look like it, no markings). I have located some nice +0,50 pistons at a good price. Would that be acceptable/good?
4.- As I am already there, what else should be addressed? I was not planning to take the engine off and open the cases, but I´m not far from that, and I would be doing the job myself, so thinking of: 
- New valves? I will take the head to a reputable shop to do a leak test on them, and replace seals and check guides. Is there any benefit in changing valves?
- Bottom side tear down to check?
- Timing chain? 
- Others?

Downside of this situation is more cash and more time to get the bike running, upside is the chance of making the motor perfect

Would definitely love some advice. Thank you in advance.

Cheers.

Carlos
 

Everything looks fine apart from the hole.
Looking at the corresponding patch of blown combustion chamber material between the valves on that cylinder towards the plug hole ( which will cause no problems going forward ) and no other witness marks evident on the crown, bore or head which would have been unavoidably made by a foreign object it was certainly solely the result of detonation/overheating caused by a very weak mixture .
This was probably due to a carburation fault/blocked jet or air leak on that carburettor or carb boot.
Chances are the majority of the missing alloy exited out of the exhaust as molten particles over a prolonged period and little if any entered the cases.
A proper engine strip, good clean and inspection of the internals will probably find no other damage. 
It's 99% that the bores are stock and depending on mileage, valve wear and straightness etc all that may be required is a general overhaul, valve job and new pistons etc.
An inspection of the associated rods little end for signs of overheating and scoring of the pin bore are the only areas of concern.

 

I can't offer much that zed1015 hasn't already mentioned, but if it were me I would be pulling the engine and splitting the cases to look for any evidence of damage or for possible remnants of the piston.   Check everything to verify still within specification and re-use if so.  Change #2 piston, valve seals and gaskets.  Use OEM parts if possible.

Take the engine parts to a vapour blaster to have them cleaned.

Doesn't look like a overheat melt hole to me. I would expect the hole edges to be have a more uniform slopeing face. Looks more like it's been punched out by some foreign object loose in the cylinder.
Drop the sump at the very least to see if there's any chunks of piston or other oddities in it. 
It's been known that either maliciously or accidentally a nut or bolt has been dropped in the plug hole unbeknown to the previous owner. 

I am inclined to agree with Zed on this one (over advanced ignition timing causes "pinking" which in worst cases can have this effect) I have seen examples of foreign object contamination and normally the piston crown and combustion chamber would have several "pock" marks where the item has bounced around. this looks like a case of the mixture "exploding" rather than burning in a controlled manner as intended. Either way I would want to be sure none of the debris was lurking somewhere to cause a problem later, also when you have gone this far it makes sense to replace the cam chain unless you have evidence of when it was last changed

Hhmm maybe, either way I'd want to have a look in the sump for debris evidence. I don't think timing would affect just one cylinder there would be evidence on number 2 piston.
Could have just been wrong over hot plug in that cylinder. Seen plenty of 2 strokes with holed pistons from using "power tip" plugs. 

Just the one cylinder affected with clear signs of overheating and detonation can only be caused by a weak mixture due to an individual carb fault or air leak which this will be..
Timing or anything else common to all cylinders would show evidence of the condition on the other pistons with it being pot luck to which one failed first.
The three unaffected cylinders here show no signs of any issues except the usual carbon build up and oil burning of a well used motor.
 

Fixed your pictures to be full size . Next time click the insert all tab to complete the picture install.
  Motor wise 
  Apperance is single cylinder detonation  as ZED  discribed 
Minimal to add to ZED is pull the pan and have a look see.
I would take this time to pull the motor down and inspect and clean everything .
The cost to do this is low as you  only need a few more gaskets .
Pulling a motor is easy  especially since the head is already off and you never know what sins  may surface.
Dave
 

His engine could be died under multiple reasons or a mix of:

Wrong spark plugs
Too much ignition advance (detonation)
Wrong cam timing
Lean F/A ratio by wrong carb jeting or pot filter
Lean F/A ratio caused by leaking carb boots (see carbon build up/blow-by in and outside the ports and seal surface)

The weakest part or piston in those environment give up first!


 

Actually, quite a few of these conditions were met. 

1.- Some unknown champion plugs
2.- No air filter in box
3.- Carb boots hard as stone

Thank to all of you. 

I´ve now taken off the pistons. All of them look OK, and the inside of the crankshaft area looks immaculately clean. I will take off the sump, but I will stop there for the moment; and will not split the cases. Looks a bit complicated to me.

I´ve also taken off the valves. Mostly covered with soot. The intake valve for the broken piston is slightly "touched" in the external circumference. Possibly not seating well. I am considering changing all valves. 

I will post pictures tomorrow. 

Thanks a ton again!

Carlos  

So in summary: a poorly maintained bike.

My thinking is an air leak on that one cylinder, along with a generally lean mixture on all cylinders because of no air filter.  Detonation set in, and the hole followed.  

I would get the head over to a machine shop for a valve job, and replace valves as needed, not as a random action.  Have all the cylinders bored oversize.  Surface head and cylinder, based on need.

Needless to say, replace the carb boots, and get a proper OEM air filter.   

I’m gonna lean towards detention. If it was a foreign object the combustion chamber would be full of craters, or pock marks as Wookie mentioned.
for me a bare minimum would be pull the pan, and oil pump. Flush everything out with diesel fuel. Check the pump for in spec and or debris and reassemble.