Fiat panda - non interference engines

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Mon 5 Aug 2013 00:26
Fiat panda - non interference engines - Billhook

My Panda Fire 999cc engine seems to be quite efficient, economical and appears to suffer no side effects from being a non interference engine.

Why are all engines not designed like this so that valves and pistons do not collide when the cam belt breaks?

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Mon 5 Aug 2013 01:02
Fiat panda - non interference engines - unthrottled

Emissions.

In order to obtain a reasonable compression ratio, deep valve relief cut-outs in the piston crowns are required to avoid piston-to-valve contact in the event of cambelt failure. These cut-outs become stagnant crevices where combustion is incomplete and the unburned HC emissions are therefore high.

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Mon 5 Aug 2013 08:42
Fiat panda - non interference engines - Billhook

Thank you for that, but why did they not use the cut out technology all the time in overhead cam engines before the emission laws?

Is it possible now for instance during a rebuild to buy special cut out pistons for say an old Jaguar twin cam engine or other classic cars where the cost of a valve collision with pistons may come to many thousands of pounds?

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Mon 5 Aug 2013 13:30
Fiat panda - non interference engines - Peter.N.

All diesel engines are of the interference type because you couldn't get sufficient compression if they were not. The considerable improvement in petrol engine fuel efficiency dictates that the gas flow be as free as possible - hence the the change.

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