Bang goes my engine.

[flatdog]

Just an observation.

From what I can determine from the marks on top of the piston - or the lack of.
She has let go either on the firing stroke or when both valves have been fully closed - no bent valves or signature of impact evidence - the piston top is still intact, showing it probably did not hit the cylinder head with any force.

ie: Conrod got to the top of it's stroke and left the piston behind.
No evidence of heatsieze on the bore.(lack of water)
No evidence of blueing/scoring on the Gudgeon pin (lack of oil)

= crappy piston material.

 

[Greggers]

Hmmm ...

Piston slap is the noise caused by a piston 'rocking' in the bore as it goes up and down (a completely different noise to sex slap ...) , generally only heard in two stroke engines with longer pistons and looser tolerances. With today's generation of short stroke (therefore short skirt pistons) motors 'slap' isn't generally something you'd come across in a modern engine.

What I can see in Paddy's picture is that the pistons appears to have fractured around its circumference, and it looks like it was around the area of one of the pistons ring grooves ... It's a surprisingly clean break though, I would have expected to have seen less of the piston crown! I've had a Suzuki GT750 drop part of a piston skirt before, but for it to completely break like that is something I've never seen before.

I think it's impossible to gauge the potential damage to the head without inspection - that piston crown would have been moving at some speed, and will have been hammered up into the head, quite easily knocking the valves back into their seats. I'd be more concerned about the extent of the damage that you can't see - the bottom half of the piston could (potentially) have done huge amounts of damage to the crank and casings.

IMHO it's clearly component failure - oil starvation wouldn't have caused a failure like this without leaving massive scoring and scorching on the insides of the bore - and of course it's only on one side too...

Best case scenario:

you've been very lucky and the bottom half is intact ... New pistons, rebore and rebuild head £4/500.00 odd

worst case: crank and engine casings fooked, start thinking about a second mortgage.

Here's what I'd do after I'd whinged and whined at BMW...

1) buy a cheap hack for the winter, stay mobile, stay earning.
2) see if I could fix it myself, cost out the parts required then balance that with the offer from BMW
3) work out how much the bike is worth, then how much it's likely to cost to get fixed
4) see if I can get a S/H motor from somewhere and find someone friendly and helpful with a nice warm garage...



Just a thought - when the motor let go, did it rotate for long?? or did you de-clutch and coast as soon as it went bang?

 

[(RIP) Mark H]

If this were my problem I would try the "BMW replaces my engine" route first of all, making an increasing nuisance of myself till all avenues are exhausted, This looks like a component defect IMHO, accept nowt else except a replacement motor 1/2 the cost will still mean thousands! ( New engine is £5350; which are prepared to call it £2,500 for me (Also gaining a 2-year guarantee on the engine.). £300-400 for fitting it)

If the above proves fruitless I would rebuild the motor myself, Based on a strip, inspection and clean of the bottom end, cyl hone and rings & pistons (I would replace both) and a helicoil for the plug and valves as required if bent on the cyl head plus gaskets and seals, The right hand conrod seems not to have battered the underside of the piston and maybe OK, I guess the piston seperated and stuck at the top of the cylinder, the motor is unlikely to be scrap and a good rebuild will make your 50k engine like new, in the unlikely event the motor is an uneconomic repair I would source a used replacement motor.

*** It may be that you could obtain a discount on parts under the circumstances.....

 

[Dave Ett]

Assuming the engine is the same as all the other 'F800' bikes, you do have a slightler bigger pool of spares to search...

 

[austen_gs]

i agree this probably isnt down to an oil starvation issue. I see a lot of blown bike engines as i race a bike engined car. I have posted the pictures on our forum to get an opinion from some of the gurus. I had an R1 engine let go at the start of last season after only 7 laps since it was installed, the conrod snapped and came through the side of the block. Initially i assumed oil starvation and expected to see a seized or scored big end, but on further inspection both big and little ends were perfect. Inspecting the conrod we came to the conclusion it was purely down to component failure through damage caused by a possible over rev or manufacturing defect. I hadnt over reved the engine and had video and data logs to prove it, so i knew it had to be either done before i bought the engine or was infact a manufacturing defect.

To be honest i cant see a manufacturing defect lasting for 50k miles, maybe it did, but would be almost impossible to prove this was the reason for failure. Personally i think this is probably caused by an over rev damage, maybe when it went down into the hedge.

I'd be intrested to see a close up of the bore and piston to see if there was any thing that caused the piston itself to seize in the bore, caused the piston to shere, but i really would expect the conrod to go first if this was the case.

Then again it could be a multitude of things combining to cause the failure

 

[Timolgra]

To be honest i cant see a manufacturing defect lasting for 50k miles, maybe it did, but would be almost impossible to prove this was the reason for failure. Personally i think this is probably caused by an over rev damage, maybe when it went down into the hedge.



Then again it could be a multitude of things combining to cause the failure

Get on the lookout for a 2nd hand engine, someone's bound to stuff their bike soon.

 

[(RIP) Mark H]

For interesting reading;

http://www.google.co.uk/#sclient=ps....,cf.osb&fp=6acbe3b58fd74454&biw=1920&bih=899

 

[BenGS]

That engine doesn't look to healthy anymore Ouch! Don't they store your bike inside? I would be pretty mad if they left my bike outside at any time especially letting it get dirty.

Good luck!

 

[Greggers]

Ok - I had a ride on an early ST800 from CW in dorchester - that had an engine that sounded like a bloody tractor, a deep knocking and clanking noise ... I quizzed the mechanic there who said the engine was due for a tear down to determine the origin of the noise - I wonder if this is what is being confused for piston slap ...

TBH unless anyone has spent any time with two strokes, you're not likely to have heard proper piston slap, which sounds more like a tinkle than a knock. However, there is an acknowledged history of the early Rotax engines having too much piston/cylinder clearance, but whether such a short piston could actually 'slap' is outside my experience...

Over-revving? Not sure if that's an issue - what's the rev-limiter set at.. 9k?? I guess it depends on whether it was bouncing off the limiter for ages when it was on its side... but I think the GunMeister has guards on which should have prevented this happening anyway ...

I take Austens point about the length of time it's been running healthily for, but fatigue failure isn't something that happens straight away is it? and as has been said before for a pistons to fail like that is unusual - I've never seen one do that before...


G

 

[D6]

so, how OLD is the bike?

 

[flatdog]

so, how OLD is the bike?

Old enough to get pissed'n'broke............Sorry

 

[(RIP) Mark H]

so, how OLD is the bike?

08 I guess ......http://www.ukgser.com/forums/showthread.php?t=200926

 

[D6]

i was just wondering , as many peoples mentioned the warranty, but no one mentioned the age of the machine,
i know a defective piston shouldnt happen and bm should put it right but they will take into consideration the age of the bike?rightly or wrongly

 

[Greggers]

IMO the age/mileage of the bike is largely irrelevant - the piston shouldn't really be considered a consumable in the same way as for example a brake pad... with car engines you'd expect 100k, 150k 200k miles without such a significant component failure - many engines both car and bike can manage this...

Definitely a manufacturing fault in my book... but, the get out of jail free card for BMW is that it is outside the warranty period ...

 

[D6]

Definitely a manufacturing fault in my book... but, the get out of jail free card for BMW is that it is outside the warranty period ...

thats what i was thinking,

 

[BenGS]

Quick question to you chaps who have far more expierence with a F800GS than me. Is it normal for them to tick when idiling? Is that just a BMW thing? Just jet washed my bike, only rear left all the electrics only (BMW said it was Ok to do just before) and noticed while rubbing it down that there was a ticking noise :O not something ive heard before with my ear plugs in an Akrapovic exhaust popping

Any ideas?

 

[rick]

How long since it last ran? Alot of engines tick when cooling down.

 

[BenGS]

Left it running through jet washing and running in garage wiping it down. Fan kicked in so it must of got quite hot the bike. It must be normal as the bike has only 6000 miles so cant be a fault.

 

[Greggers]

I think that ticking at tickover is a pretty normal thing .... mine does it too!

 

[Losttheplot]

Is it normal for them to tick when idiling? Any ideas?

Probably the timing chain. my XChallenge did this when it was new, then the tensioner moved on a click or 2 and it quietend down.

Sorry to hear about your bike gunz.

Looks like the piston may have flipped in the bore- something some of the early crf mx bikes were rumoured to suffer.Mostly down to these short skirted pistons not having the vertical stability of a longer skirt.

Looks like it has flipped and the piston crown has taken out the plug (where it is cracked), while the conrod has sheared off the gudgeon pin castings on the underside of the piston as it has come up and hit the cylinder head/plug, and with the flipped piston making the whole assembly much longer, something had to give- which is the gudgeon pin castings on the bottom of the piston.

good luck with getting it sorted.