Broken piston ring and a cracked cylinder head

[joffco]

Hi

I need advise. My 2003 KTM 625 SXC has a very strange problem. Ever since I got the bike (I´m the 3rd owner) it has been making a very strange noise when I shut it off and the rpms falls. I sounds like detonation or something. First it freaked me out but the bike ran perfectly and everything seemed ok, except the automatic decompression has never really worked. I rode the bike for a year and had no problems at all. Then it started blowing white smoke so I decided to tear into the top end.

What I found shocked me. The top piston ring was broken into at least 30 pieces and the cylinder head was cracked (explains the white smoke). The bike was still running strong, I rode it home and then tore it down!!!!

I have always used good quality gas and never noticed detonation when riding. I have never even boiled it over!!!!

So if anyone has any ideas I am all ears, I'm stumped????

Thanks,

Jon

[Island Hopper]

I had the piston and top ring break on my 03 Adventure and have heard of a few others.

I tore the engine down right away after it started sounding strange and found a lot of damage stemming from what I think started with a broken piston ring. My engine worked fine for over 40,000 km and then with no explanation the failure took place... It still ran with the damage but it was very noisy and you could hear that the crankshaft was bent {as I found out after teardown}.

The noise upon shutdown is normal as my bike makes it as well as a few others I've heard..

[dorkpunch]

OUCH! The *clank* *clank* on shutdown is normal- just the auto decomp banging around. where was the head cracked?

[joffco]

The head has a hairline crack between a intake valve seat and a exhaust valve seat. Those two are very close together.