Technical MultiAir Interference

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Technical MultiAir Interference

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This is not a specific Punto question, but since it (Punto Evo) is the first car to receive this engine, it makes sense to ask here (or possibly 'Grande Punto' section, why couldn't they just carry on with the regular naming convention?). Is the new Fiat MultiAir engine non-interference? The reason I ask is that the valve actuation is electronic, and I wouldn't fancy the Fiat electrical gremlins causing a piston-valve scuffle.

I've spent quite a bit on my car over the last two years, and if anything major goes wrong again, I am going to have to consider whether it is economical. I would consider a Punto Evo MultiAir, but not a chance if it is an interference engine :devil:
 
The valves probably fail shut so maybe less catastrophic when it does go t*ts up.

Courtesy Google: http://www.fiat.co.uk/Content/?id=10857

Personally I would like to see turbocharged 2 stroke diesels. They dont use the crankcase for breathing so they dont clatter like scooter engines and are amazingly powerful. They also dont need poppet valves, cams, mutiair, etc
 
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The valves probably fail shut. I cant see how that makes it more reliable though maybe less catastrophic when it does go t*ts up.

That would be safer in the event of a power failure. However, if someone in the ECU programming department has not taken into account cumulative rounding errors or memory leaks when it comes to the engine phase variable, the engine could quite easily fall 90 degrees out of phase, much like a cambelt jumping teeth.
 
It works by leaking oil out of the inlet cam followers so if the cam drive fails at the very least exhaust valves will hit pistons.

Dirty oil will be a nightmare
 
The new MultiAir engines have electrinic inlet valves. The cam belt only drives the exhaust valves. As the inlet valves are opened electrinically I dont believe there is an inlet cam? The cam belt should be under less stress than a conventional engine so cam belt failures should be rare.
Whether engine is interference or non inteference I dont know. A lot of toyota engines are inteference. Cam belt failures and valve colisions are rare on Toyotas. It all comes down to good design and good maintenance.
 
The MultiAir is an evolution of the 1.4 16v FIRE engine which was always an interference engine- I'd put good money on the MultiAir being no different.

There's plenty of presentation video's on Youtube that show the basic operation of the system.
 
Pretty much every 16V engine is interference. Soft cams and light valve springs will put less strain on the cam belt. Fiats tend to rev so need harder springs, etc.

According to the diagrams on the www all valves on the new engine are driven by one cam shaft so the cam belt load is the same as any other engine. The difference is the special hydraulic tappets which vary the lift and duration of the inlet valves opening.
 
Technically only 8 valves are driven by the camshaft, with 4 other lobes being used as a pump to create pressure in the hydraulic lines which feed the solenoids for the inlet valves.



;)
 
Danny, that video is fantastic thank you. As you say, the intake camshaft now effectively acts as a pump, but only provides pressure at times where the piston is not at TDC, so an electronic failure of the phase position could open the solenoid at the wrong time, put there would be no pressure to open the valve. It's significantly more fail-safe than I expected. It does require the engine oil to stay pretty clean though I imagine.

Still pretty scary watching how close the valves and pistons come.
 
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I wonder how Yamaha manage to get 120bhp and 16000 revs from 600cc. To get that much air in and out, all of the valves must virtually touch the pistons.
 
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