Spun a big end shell and piston hit head ??
Discussion
Just trying to understand if this is possible.
Just picked up a Cosworth YB engine in bits, i have known about this engine for the last 17 years.
Anyway the story was it spun a shell on no3 and in turn the piston has contacted 2 of the valves on that cylinder and bent them.
Thinking out loud here how can a bearing spin and increase the stroke of the rod to contact the piston.
The guy fitted a donor engine and kept the duff one in his garage ever since. I have been asking him to sell it since then and last night I managed to get it off him.
Just picked up a Cosworth YB engine in bits, i have known about this engine for the last 17 years.
Anyway the story was it spun a shell on no3 and in turn the piston has contacted 2 of the valves on that cylinder and bent them.
Thinking out loud here how can a bearing spin and increase the stroke of the rod to contact the piston.
The guy fitted a donor engine and kept the duff one in his garage ever since. I have been asking him to sell it since then and last night I managed to get it off him.
chippy348 said:
Just trying to understand if this is possible.
Just picked up a Cosworth YB engine in bits, i have known about this engine for the last 17 years.
Anyway the story was it spun a shell on no3 and in turn the piston has contacted 2 of the valves on that cylinder and bent them.
Thinking out loud here how can a bearing spin and increase the stroke of the rod to contact the piston.
The guy fitted a donor engine and kept the duff one in his garage ever since. I have been asking him to sell it since then and last night I managed to get it off him.
Sounds like complete bJust picked up a Cosworth YB engine in bits, i have known about this engine for the last 17 years.
Anyway the story was it spun a shell on no3 and in turn the piston has contacted 2 of the valves on that cylinder and bent them.
Thinking out loud here how can a bearing spin and increase the stroke of the rod to contact the piston.
The guy fitted a donor engine and kept the duff one in his garage ever since. I have been asking him to sell it since then and last night I managed to get it off him.
ks to me. Valves and pistons meeting is usually because cambelt went ping.I would agree it does sound like a load of cobblers.
I've got a (different I know) engine from a Fiesta ST150 which has spun its shells, it made a terrible knocking noise as there was whitemetal removed from the shells, I guess a lot of material would have to be removed to allow enough movement of the piston to hit the valves.
Is the YB an interference engine? Are there marks on the piston from the valves?
I've got a (different I know) engine from a Fiesta ST150 which has spun its shells, it made a terrible knocking noise as there was whitemetal removed from the shells, I guess a lot of material would have to be removed to allow enough movement of the piston to hit the valves.
Is the YB an interference engine? Are there marks on the piston from the valves?
chippy348 said:
Just trying to understand if this is possible.
Just picked up a Cosworth YB engine in bits, i have known about this engine for the last 17 years.
Anyway the story was it spun a shell on no3 and in turn the piston has contacted 2 of the valves on that cylinder and bent them.
Thinking out loud here how can a bearing spin and increase the stroke of the rod to contact the piston.
The guy fitted a donor engine and kept the duff one in his garage ever since. I have been asking him to sell it since then and last night I managed to get it off him.
So you're asking how the travel of the piston would change when a big end bearing shell spins and gets destroyed...going from say 2mm thick to nothing ?Just picked up a Cosworth YB engine in bits, i have known about this engine for the last 17 years.
Anyway the story was it spun a shell on no3 and in turn the piston has contacted 2 of the valves on that cylinder and bent them.
Thinking out loud here how can a bearing spin and increase the stroke of the rod to contact the piston.
The guy fitted a donor engine and kept the duff one in his garage ever since. I have been asking him to sell it since then and last night I managed to get it off him.
At a guess it may affect travel by say...2mm ?
Whether that is actually the cause of damaged valves or not will be found on inspection, but pistons hitting heads when big ends get destroyed it quite common ( when people continue to drive for long enough of course )
I picked it up last night, it is already part stripped so that is how i know.
Today i have looked at the head and there are 2 bent exhaust valves and the piston has tapped the head face. There is no further damage to the other pistons or valves.
Thinking about it if the big end has gone then it may throw the rod up more as its no longer fully connected to the crank.
I have removed the 2 valves and put the head in the hot wash for the day, the piston is in the de-carb will post photos later.
Today i have looked at the head and there are 2 bent exhaust valves and the piston has tapped the head face. There is no further damage to the other pistons or valves.
Thinking about it if the big end has gone then it may throw the rod up more as its no longer fully connected to the crank.
I have removed the 2 valves and put the head in the hot wash for the day, the piston is in the de-carb will post photos later.
Once oil pressure is gone metal goes to metal (crank on bearing) they wear each other away rapidly until they get so hot they bond together.
Because the crank has grabbed the bearing it spins it in the rod causing more wear. At this point it's bad enough as the crank and rods are junk.
If you carry on then the bearing can bond to the rod, depending on a few more factors it bends and breaks then exits stage left through the block to create a little window so you can look inside.
^^ Now can you see how a piston can hit the head? Bending a valve depends on how close they were obviously, piston to head is usually .08 - 1mm cold, so if the valve was less than that it'll bend that too.
Because the crank has grabbed the bearing it spins it in the rod causing more wear. At this point it's bad enough as the crank and rods are junk.
If you carry on then the bearing can bond to the rod, depending on a few more factors it bends and breaks then exits stage left through the block to create a little window so you can look inside.
^^ Now can you see how a piston can hit the head? Bending a valve depends on how close they were obviously, piston to head is usually .08 - 1mm cold, so if the valve was less than that it'll bend that too.
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