Duke 125 engine failure

[Bakazan]

The engine on my Duke 125 let go this morning. The bike was down on power, just about holding 60 when normally it can do 70. At the point of failure I had screeching whirring noise along with instant loss of power. Pulled the clutch and drifted to the side of the dual carriageway.

AA were brilliant at getting me home. The recovery guy said he thought it sounded like there was no compression.

This afternoon I lifted the cam cover expecting to see a mess / lack of chain but all looked well.

I removed the spark plug and all did not look so well...



Clearly it has been smashed over so I guess the piston or a valve let go - any ideas what might have caused this if the drive to the cams all looks intact?

I guess the next step will be to drain the oil to see how grim it looks.

I suppose out of curiosity I will strip the top end down to see exactly what happened.

Any views on repair vs secondhand engine? If the piston is holed is it likely bits of metal have made their way to the gearbox?

This was on an engine that had only done 6400 miles.

Any thoughts or advice would be welcome.

[Megaflow]

Piston or rod failure.

It needs stripping for more than just curiosity. Needs stripping to find out what has failed, only then can you
Make an informed decision or repair vs replace.

Have you owned it from new?

[Krikkit]

Bakazan said:

The bike was down on power, just about holding 60 when normally it can do 70...

...Any thoughts or advice would be welcome.

This was the point when you should've turned around and gone home!

Unfortunately sounds like rod/piston as above, as something has definitely smashed that plug, you have my sympathies.

[Bakazan]

I bought it secondhand from a dealer about 18 months ago.

The engine always felt more agricultural and less eager than I was expecting, although I'm comparing that to 2-strokes in my youth and a 600cc sports bike for most of my riding life.

[Bakazan]

Krikkit said:

This was the point when you should've turned around and gone home!

Unfortunately sounds like rod/piston as above, as something has definitely smashed that plug, you have my sympathies.

In hindsight yes, but it's quite difficult to diagnose a problem when the bike just doesn't feel "right". I didn't anticipate catastrophic failure.

[Chipchap]

For a piston to actually reach a spark plug that usually means a big end failure that then allows the extra distance to travelled. The screeching is when the shell or bearing finally has had enough. I would surprised if there is any oil in it.

[Eatpies99]

My apprentices Duke 125 broke down last year. It had melted a valve...

[Megaflow]

Chipchap said:

For a piston to actually reach a spark plug that usually means a big end failure that then allows the extra distance to travelled. The screeching is when the shell or bearing finally has had enough. I would surprised if there is any oil in it.

To damage the plug that badly would need more than a main bearing failure. The reason I asked the question about had he had it from new, might also explain the not feeling as quick as it should. I’ll bet it has been hydrolocked, bent rod = less compression and less performance, followed shortly after by rod failure.

[catso]

Megaflow said:

To damage the plug that badly would need more than a main bearing failure. The reason I asked the question about had he had it from new, might also explain the not feeling as quick as it should. I’ll bet it has been hydrolocked, bent rod = less compression and less performance, followed shortly after by rod failure.

I had a KTM 500 (2-stroke) on which the little end bearing failed and before seizing due to the rollers getting sucked into the intake ports and getting embedded into the cylinder walls and piston, said piston smacked the cylinder head and the rod was bent but, IIRC the spark plug was untouched...

[ThreadKiller]

Couldn’t a dropped valve do this damage?

[catso]

ThreadKiller said:

Couldn’t a dropped valve do this damage?

Quite likely I would think, once hit by the piston it could move into the plug?

[Megaflow]

catso said:

Quite likely I would think, once hit by the piston it could move into the plug?

Possible, but unlikely. Dropped valves generally get stuck in the piston or head very quickly.

Either way, it is all coming apart so we will soon know.

[Birky_41]

Its a KTM...are you surprised? As said it'll have snaped/cracked or melted something due to their 'workmanship'

[ssray]

You can fit a 390 now

[Biker's Nemesis]

Electrical failure

[Bakazan]

Thanks for all the comments and theories, it will at least be interesting from an engineering perspective to see what happened but it might be a while before I get around to removing the engine.

ssray said:

You can fit a 390 now

Unfortunately not as I bought this bike for my wife who was intending to ride it on a CBT. She didn't get around to re-doing her CBT last year so I've destroyed it before she even got to ride it!

However on a linked point does anyone know if there are any electronic restrictions on swapping the engine with another from a Duke 125 / RC 125?

[Krikkit]

I believe they're identical across the range, but I'm sure there's slight changes year-to-year.

What I'd do is have a good scope at the parts diagrams on someone like Fowlers and see if you can spot loom/sensor/mounting changes.

[LordFlathead]

Birky_41 said:

Its a KTM...are you surprised? As said it'll have snaped/cracked or melted something due to their 'workmanship'

KTM or Killed the Motor as is becoming commonly known as.

Engine rebuild at best or new motor depending on damage and amount of circulated swarf.

[bimsb6]

Megaflow said:

Chipchap said:

For a piston to actually reach a spark plug that usually means a big end failure that then allows the extra distance to travelled. The screeching is when the shell or bearing finally has had enough. I would surprised if there is any oil in it.

To damage the plug that badly would need more than a main bearing failure. The reason I asked the question about had he had it from new, might also explain the not feeling as quick as it should. I’ll bet it has been hydrolocked, bent rod = less compression and less performance, followed shortly after by rod failure.

You managed to read big end and quote mains ,

[Biker's Nemesis]

There's a big difference.