Hi, I need more opinions on the cause for this engine failure. Some history: The bike is a 1098S and was bought with a complete engine overhaul. Pistal pistons Arrow conrods New bearings Balanced crank Flowed head With 3000 km i had the engine stop at the track... Here some pictures of what i found: I allready i have an idea of what was the fail. I want to know other opinions. Thank you for your help Pedro
well from the limited photos it does look like a piston failure. but interesting in image 1 looking at the piston in the barrel there does seem to be a large shadow between the piston and the bore around the top half of the circumference. certainly looks unlike rebores I have had done in so far as the bore looks too big. if that was the case you would get excessive piston rock/vibes and create more stress. but youd have noticed that from day one as it may also have had a slapping noise. >but< probably just the way the pistons sat with the skirt being fubar'ed and micrometer to confirm. but if that was me id measure the piston and bore as it visibly looks wrong. possible barrel failure - the barrel skirt could have cracked and destroyed the piston. did it burn oil. have any in ay the time of the failure...
you never know but I dont think its a clip. if the gudgeon pin worked its way out one side id expect to see more damage on that side where the material would have failed more. that break on the piston is fairly uniform. considering pistal pistons are very strong compared to stock I am surprised at this as a failure because of the super quality of the piston. OP were they stock size or was this a high compression oversize rebore and nicosil replate job. what does the outside of the piston skirt look like any wear around the very top and bottom of the slipper skirt
Jeez that looks nasty . Sorry I cant give you any idea of the cause. All I can hope is that you were okay when it happened and that you can get it fixed for a reasonable amount of money
I agree that looks a gudgeon pin clip failure, though the area around the small end on the piston may have started to fail first. If most of your 3000miles since the rebuild were on track, then it's not so surprising.
I'd go for piston failure as well. When I've seen gudgeon pin clips fall out/not fitted, there's normally some wear to the bore on the side the pin works its way out? Having said that, on the first picture the piston is marked on the right side where the gudgeon pins could've worked out? It looks like the piston has then failed and the con rod has done the rest. Either way it's pretty fecked!
I you look at the right(?) hand side of the piston it looks like the piston pin bore has torn along its centre line, but the left hand one looks like it has it has torn further away from the piston crown. Difficult to say from photos and probably not much easier with the bits in your hand. As you also say these pistons are really good quality and I would be surpised if the piston material around the piston pin has failed, but if it has live its life on the track maybe this could be the case. Maybe the OP could have a look at the other piston and see if there are any problems starting there. Im going to have a good close look at mine before putting them back...
whatever happened, it's all about the small end area. Biggest tell-tale for me is the matted face of what's left of the piston gudgeon pin housing bore.
This sort of damage can often be the result of interrupted oil supply/oil starvation to the upper cylinder, the piston overheats, nips up and at high revs and temperatures, the rod tears the small end out; always a mess.
Thank you for your thoughts on the matter... I'm going also for a circlip failure or not instaled. If you can see from the pictures the right side of the piston where there is the groove to put the gudgeon pin is marked and also the side wall of the cylinder ir scored vertically. Was built by a reputable shop in the UK They are original cylinder from a 1098. The piston was a normal wear from 3000 kms If it was a piston failure would the pin should be in the rod? Why is in the crank? There was no knocking sound and rattles, i was on the first lap of the 3rd session and heard a hiss and felt some thing in my left leg, pulled the clutch the engine stopped and coasted. The hiss was the pressurisation of the water circuit because of the rod goint thru the cylinder wall. I was lucky in being upright and going slow....
Hi John, Would it cause the gudgeon to move? The gudgeon pin doesn't have any discoloration from heat...
its strange you would have to see the sides of the bore, so if it was the pin comming lose and jaming the side of the piston it would show on the bore side , i have heard of a clip comming out and jamming the piston . you would have to see all the damaged parts to see if there was metal to metal transfer
now you tell us - this all helps you know! - there's an area where the piston gudgeon pin housing has detached (only one out of the 4 'break' faces) that looks unusual. It's hard to see but unless it's been 'kissed' by something it looks too clean for a tear or break.
