Went for a ride today, usual nonsense on my 04 280 Pro when I break off the shift lever. So I think no big deal I'll just play around in 1st for awhile. This worked great until 15 minutes later the top end starts making a terrible noise and the bike starts struggling then dies. This is all at idle and I really was not doing anything different than normal. I pulled it apart and the top of the piston on the exhaust side broke off along with the rings and all the other exciting things that happen. So why would it do that?! Its been running fine for months.

Other possible relevant information...

I use 91 Octane non ethanol gas, mix 4.25 oz of Schaeffers Premium two cycle oil to 2.5 Gallons of gas aiming for slightly richer than 80/1. The head also has a 1mm spacer to lower compression.

I was about halfway through my newly mixed tank of gas, air filter was changed a few rides ago.

I am just lost as to why it would do this unless this is a common thing and that just happens when the bike gets 14+ years old. What I don't want to do is get a new piston cylinder and head and have it do the same thing because I am missing something. Any thoughts would be appreciated! Thanks.

 

 

 That colored splatter looks like big end rod bearing. Grab the rod and feel for play.

There may be a very very slight amount of play straight up and down and it has some side to side play. The big end bearing sounded and felt a little grainy to me but I don't know if that is just piston pieces in it or if it is actually failing.

OMG sorry to see that carnage.

Looking at the fracture line on the piston, there is a good amount of carbon on it, so that didn't happen in just five minutes.

It could have been caused by something jamming in the exhaust port, many months ago.  Or that the piston was dropped on the floor on its edge, during initial assembly.

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Edited February 4, 20188 yr by scifi

Try to pick the pieces out of the piston and see if they are pieces of alloy or steel. If steel then its either ring or roller, if alloy, then piston or roller cage

My guess is, the piece of the piston crown has broken away a while back, and this time was the the exposed ring catching in your port, so you lost compression and the broken piece caused the further damage

Edited February 4, 20188 yr by faussy

That is a very good point. I didn't notice the carbon on the broken edge of the crown. I will pull the cases apart today to get a better look at the crank and likely pull pieces out of it and the crank case. So would this be something I did to it or just a unlucky failure? No one seems offended by the gas and oil I use which is a good sign.

Judging by the carbon on the piston where a bit is missing, it looks as if it has been missing for some time. This would expose the top ring to excess heat and it would flex up and down, eventually fatigue cracking and breaking off.

You need to find out if the big end is failing. As the engine is now 14 years old the big end should probably be replaced along with the mains and seals. I have known several instances of big end bearing cage parts causing this type of damage, even though the big end rollers and bearing surfaces were still OK.

Any chance the piston was in backwards (i.e, the orientation arrow was facing backwards)? I ask because two items in the picture catch my eye (but I apologize it's kinda difficult for me to see clearly): 1) It appears that the top ring opening "notch" is toward the front (and what I see is not the result of a broken ring), and 2) It appears that I see what could be the ring retaining pin in the area of the fracture. Over time a piston will develop a fore/aft "rock" and an incorrectly oriented ring could eventually snag on the exhaust port. And then things go south very quickly.

So perhaps carefully clean the top of your piston and try to determine how it was oriented. And do try to find the missing piece lest it lie in your crankcase waiting to ambush you.

Dale

Dale I think you are right. I cleaned the top of the piston and found a triangular arrow (in the right side of the picture) that was definitely facing the intake side of the cylinder. Should be flipped around right? The other thing I noticed is it is a Vertex piston. Is this stock or did a previous owner install that in backwards? Can you get over sized pistons for these bikes or am I looking at both a new cylinder and piston rather than boring to OS?

Dadof2 when you mean the big end is failing do you just mean it would need a new roller to freshen it up and call it good or does it wear on the journal of the connecting rod?

Thank you all for the advice I really appreciate it and hopefully I get this thing running around again!

 

 

Piston was in back to front.I wonder if you might be better off sourcing a replacement engine,it might be cheaper 

If you have a pic of the piston before you removed it from the rod, you could tell.

My understanding is that the cylinders are plated and that one does not want to bore them. Rather the cylinder surface is lightly honed if not too worn or damaged. You would then install the next larger piston (A to B to C to D). I have no experience when it comes to changing the big/bottom end bearing.

It is a new rod kit if the big end is bad. Sure it will cost, but still cheaper than another bike. A Fresh 2 stroke is always good.

I remember when you were having Ducati ignition problems you were doing some weird wiring experiments, bypassing components. I wonder if this was the initial cause with improper ignition timing?

Usually trials bike top ends don't need to be replaced even after 10-15 years for the average rider with proper maintenance and the usual putting around. I never hear of trials riders installing hour meters and talking about new rings or piston after X amount of hours like I hear enduro and mx riders do.