Mitsu 4D56 advie-Interference or non-interference engine?

[arnielbenz]

Mga sir heto na naman po ako nagtatanong hehehe!! ask ko lang kung lahat ba ng position ng piston sa mitsu advie 4D56 ay kung Interference or non-interference?

Base kasi sa nabasa ko, In an interference engine, the position of the piston at the top of its stroke will occupy the same physical space that the open valves do whilst the piston is at the bottom of its stroke. It's important to know if your engine is an interference engine because if the timing belt breaks, at least one set of valves will stop in the open position and the momentum of the engine will ram the piston in that cylinder up into the valves requiring a very expensive engine repair or replacement. In a non-interference engine, the valves do not occupy any space that the piston could move into, so if your timing belt snaps on one of these engines, in 99% of cases you won't suffer any valve damage because the piston cannot physically touch the open valves.

Salamat mga sir.

[voltscastillo]

alam ko interference engine ang 4d56 eh. kaya salpok talaga yung valves sa piston pag napatid yung timing belt at high revs.

[duskylim]

Dear Sir:

You must have misunderstood the explanation. The valves CANNOT occupy the same positions at top and bottom dead center because then they will NOT be moving!

Which means they will not open and close, which means they will not be serving as valves in the first place - the means by which the engine controls charge flow into and out of the cylinders.

What is usually meant by an "interference engine" is that at TOP DEAD CENTER the valves and the pistons are in close enough proximity to ALMOST touch.

This is typically the case when the clearances between them are very close, such as in diesel engines with very high compression ratios - greater than 19:1, or in older model gasoline engines with severely hemispherical combustion chambers and high-lift, long-duration camshafts (race or semi-race cams) - a good example of which is Toyota's 2TG with the Yamaha head.

What is usually done (for both the diesel and gasoline engines) is that pockets are cut into the piston crown to create clearance for the valves at top dead center.

These cuts are called FLYCUTS or RELIEF cuts. Open any issue of Hot Rod or Diesel Power magazine and you can see ads for these type of pistons - usually offered by the Arias piston company.

As we are talking about the 4D56 (a Mitsubishi diesel engine) the reason for the high compression ratio (from 21.5:1 to up to 23.5:1) in these engines is they are DIVIDED Chamber or Indirect Injection engines.

They need the high compression to generate the necessary heat and turbulence for complete combustion at high engine speeds (>3000 rpm).

This was the traditional solution back then for high-speed automotive diesel engines (pioneered in the Philippines by the Isuzu Gemini Diesel).

This was the older design that was popular before the advent of the more modern Common-Rail, Direct-Injection (computer-controlled) diesel engines.

These older engines have a small, spherically-shaped combustion chamber (called a TURBULENCE Chamber) which communicates with the main chamber via a narrow throat - the most common design of which is the RICARDO COMET Series III, IV and V.

The chamber also contains the injector nozzle and the glow plug. During compression, air at high speed is forced into the turbulence chamber in a spinning vortex.

Injection begins a little before top dead center and the combustion causes a reversal of flow out of the chamber into two pan-shaped cuts in the piston, completing combustion.

As high compression ratios demand close tolerances, there is little that can be done to minimize interference. That is why all these engines are at risk of self-destruction should the timing belt break.

It is false economy to skip or neglect your timing belt. Change it at the recommended intervals.

Best Regards,

Dusky Lim

[Dieseldude]

Guys, thank you for your posts re interference and non-interference engines. I was never aware of these terms.

Let me share my experiences on 4D56 timing belt failure.

This engine has two timing belts, short and long belts. Short belt is driven by the crankshaft to synchronize the left and right balancer shafts. This minimizes engine vibration. Short belt failure rarely does any engine damage, except for increased vibration. Long belt synchronizes crankshaft, camshaft, and injection pump. From experience, long belt failure may or may not result in catastrophic engine damage, depending on the operating state of the engine during belt failure.

1. Vehicle running fast or downhill, transmission engaged: When belt failure happens under this condition, injection pump and camshaft stop turning while crankshaft continues rotating due to vehicle momentum. Any valve which is in the open or down position will be repeatedly hammered by the piston, resulting in major engine failure.
2. Vehicle running at low idle, transmission not engaged: When belt failure occurs under this condition, both camshaft and injection pump stop turning, and crankshaft almost immediately stops rotating. Although the piston may hit any open valve, the force is not sufficient to cause any significant damage due to low flywheel inertia.

Sad to say, most timing belt failures occur when vehicle is on the road with transmission engaged................

As Dusky posted, replace timing belts on schedule..

[kgb]

All what you have quoted is technically correct but very unnecessary,all 4-stroke diesel engines are interferance engines by design,if the synchronisation between crank and cam is broken there is serius trouble guarranteed!