SV650 piston hitting spark plug?

And the divots in the top of the piston don't look all too healthy either...

 

Those are from the spark plug getting pounded.

 

with bits of piston in between .

 

We have a winner. Guess I didn't annotate the photo, but Venom is right. The two portions of piston head are broken off right underneath the intake valves. The shiny stuff you see are the piston rings which should not be visible.

A photo from an angle would have shown the damage better I suppose, but it is what it is. Just took the picture as a courtesy to those who were hanging around this thread with interest.

Now all that's left for me to do is find out just how much ancilliary damage ensued. Fun, fun, fun.

 

Yeah.. They were foreign....Made in Japan

 

I'm just not convinced those pieces would have broken in the valve hit the piston.

Are the valves bent? Do they show impact damage on the valve?

 

Ok I see it now. The broken parts looked so neat and symmetrical that I thought maybe it was some kind of different piston. I have only seen a few and I couldn't tell that the shiny spots were actually the rings.

 

Well I had several things going on today, so as soon as I got the cylinder head off and observed the clobbered piston head I took a quick photo and posted to the beeb before heading out for other business.

Since my last post I've had time to take a better look underneath the head and you've got a point. The valves look just fine. I'll pull them out soon enough and get a better look at things, but there is no sign that the valves ever touched the piston.

Add to that the fact that I thought about it some and realized that intake valves would not "float" long enough to contact the piston. They close before the piston starts the upstroke or you wouldn't have compression. Only exhaust valves would be able to float during the exhaust upstroke.

Which begs the question. What could have clobbered the piston head in exactly those positions if not the intake valves? It seems we've traded one mystery for another.

 

What fuel had you been running? Is this a stock motor?

To me you could have been running extremely lean causing the piston to get very hot and then fuel could have detonated in the ring groove causing the piston to blow out.

I was shown by my engine builder a cast and a forged piston that did just this. The cast one looked similiar to your piston, just not as much of the piston was blown away.

So look at the edges of where the fracture is. Can you maybe tell if there is a grain and which direction it looks to go?


Oh and I would fully expect the valves to bend before the piston would fracture but I don't have the experience to say otherwise.

 

Detonation, period.

 

Interesting. I have heard of the top of the piston coming apart in SV's but have never seen it... until now. See how close the back of the ring groove is to the valve cutout? I would guess your unintentional "death rev" was just enough force to fracture the piston in an already weak area. It may be that the piston didn't contact anything, valve or head surface. But if she spun up to 13k rpm or whatever for a couple seconds, that's a lot of g-force on a cheesy cast piston. It could also be that the intake valves whacked the piston, it is possible. Normally there is a ton a valve-to-piston clearance on a stock SV, but again, with the death-rev, who knows.

With the bike being ridden since the initial incident, any witness marks in the carbon will be gone.

 

To my knowledge the engine is stock. The bike has a full Yosh exhaust and I know that the previous owner had a local "good ol' boy" with a dyno spend several hours tuning the carbs for more power, but unless another previous owner had something done to the engine it's stock.

I'm not aware of it having anything other than pump gas in it, but once again I'm at least the 3rd owner.

Looking into the crystal ball I see myself going to eBay in search of a piston and possibly a cylinder and other parts.

Or do you guys think I can buff that right out?

 

That looks like a job for some "Mighty Putty"!

 

There is the word I was looking for.

 

i have seen a couple SV pistons break at the same spot, it is the weakest spot due to the valve relief. Detonation usually. And you are lucky one of those chunks did not get caught in a valve.

 

It'll buff out. Just use this Buffing Compound.

 

D D D D D DET TON NATION IS A COMPLETE WHACK!

Peak det happens between the dome and the side electrode.

You pull a plug and tiny gray spots are melted or show shadow that it melted and vaporized off is the mark of the aluminum.

I want you to show me the det at both cylinders, or show me how one piece flew out, compressed the plug flat.

How can you say it was for sure detonation without checking the valve lash or the valves showing a tag, or leaking first at the valves being bent and detonation does not bend valves. :wow:

WE on the same page is in steps to conclude the det?

1. Where is the damage to the peak spot where plug side to dome would show first blow?
2. Where is the ding to the valve tag?
3. If det is so violent and the pockets are week, how come all the months go blow bye with minor det that just knocks?
4. I see a clean dome with zip for det at this time.
5. Why with all that oil, did not more det occur with all that oil out into the cylinder?
6. Where is the det to continue the hammering of 120 miles?
7. Could the loss of compression not cause damage since the kinetic is on the rise but through the ring and not too much of a compression to friction up the wall is now add a fuel to fire a D D D D D DUDE?


i'M inn A JUST Azzkicking mode.

 

Bah! no need for that, once those loose pieces aren't in there the spark plug gap wont get closed anymore and it should be fine

 

You laugh, but if you were stranded in the middle of the desert, you could bolt it back together and ride to town no problem (presuming you were not racing your buds back)..