how did this engine damage happen then?

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how did this engine damage happen then?

Can't see a valve bending unless it's been whacked by a piston. But, looks like the valve seat has cracked taking a bit of the head with it. And it looks like the exhaust side.

Guess: valve float allowed piston to clip valve, leading to damage to head. Or, valve guide and valve stem seized together, piston clipped valve, yada yada.
 
i was blind yesterday :eek: there is a small mark on the piston.

one valve stem oil seal seat is gone and all the others are not sat on their seats no more all moved up. i know they was all on tight because i helped him build the head back up after the skim :confused:

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Oil seals wont cause damage just burn some oil. I would vote for a blockage in the water circuit in the head maybe that siezed the valves it would certainly get up to plug lead melting temps. Mixtures all look fine and if the timing was good it has to a cooling fail. Not hydrolock, the valves have to be shut for that so it's the conrod that goes, also to get a cylinderful of water in one cycle it has to come in from the road via the air inlet
 
Sorry Dave, meant to say before. Water in the cylinder will not do much, if any harm but it does tend to scour the coke out.Believe it or not braver men than me have decoked cars with a garden hosepipe to the air inlet. Water injection was used on aero engines, usually for getting things likie B29s airborne.
 
yeah ive seen water used to clean the engine out, it's fine if done properly. and water mixed with ethanol injected in the right amounts will ward off det nicely :)
 
what has happend there (imho) is the valve seat has come out (can happen)
it has dropped out and done a load of damage as the valve hammers it back in

If you look closely there is a space between the seat and head. this would happen as the seat takes chunks out as its been slammed back into its hole by the valve. it might seem ok now (wont come out) as the head has cooled and tightened back around the seat.

used to happen a lot on old brit bikes.
 

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Yeah, I think the valve seat has a part to play as well. Used to happen on the horizontal cylinders (only) on Ducati V twins (the bevel ones) if you splashed through a big puddle following a thrash. I thought it was a myth 'till it happened to me.

Although theoretically recoverable, I think a "new" head and a careful look at the bottom end is called for.
 
what has happend there (imho) is the valve seat has come out (can happen)
it has dropped out and done a load of damage as the valve hammers it back in

If you look closely there is a space between the seat and head. this would happen as the seat takes chunks out as its been slammed back into its hole by the valve. it might seem ok now (wont come out) as the head has cooled and tightened back around the seat.

used to happen a lot on old brit bikes.
Good point I hadnt looked at that pic full size and I'm sure you are right. The fact that both exhausts are showing a bit of detachment could have been cause by local overheating again, the head exanding too much as it goes over its design temp . If you bend a valve you can take that plug lead off and limp home, you wont melt all the plastic on the engine. I agree that a new head and you are good to go, that one is scrap.
 
Just a thought, see if my logic works

over heating caused by either pinking or coolant leakage. As the coolant starts to evapourate in the head (where the most heat is to begin with) causing localised hot spots. The cylinders towards the rear of the engine start to suffer the most., Material starts to burn and valves start to stick but the block is still being cooled, just enough to prevent damage, Hot, sticking, weak valves kiss the piston and bend ever so slightly before re-seating

Any good?

Jules
 
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