R22 - Lycoming engine and engine compartment

E:TIP 1:induction hose: after maintenance has been completed, use you left hand to feel up behind the air induction entry on the right hand side cowling (just rear of the pilot’s door) and check to see that the flexible air induction hose has been firmly attached. We know of a couple that have come off because the hose clamps were not tightened and then caused a consequence loss of power when the hose sucked onto something else in flight.

E:TIP 2: carb heat: If at any time in flight you feel that “something is not right” with the engine – your first action, provided that it is safe to do so (height, power requirements etc), would be to pull the carb heat full on. This ensures that any potential carb ice problems are eliminated, PLUS gives you an alternative filtered carb air source should the problem be with the main air induction hose.

E:TIP 3: power loss when hot: If at any time in flight you have an unexplained loss of power that is of a magnitude that, though the engine keeps running, an emergency landing has to be made, it may be a problem with an inlet valve and your hydraulic tappets.

This can usually be confirmed by the fact that the engine can be started and run again with no apparent problems after it has cooled down, whereas a sticking exhaust valve usually gives problems on the next cold start.

What may have happened is that the engine has, some time in the past, been started with the throttle wide open and the resulting quick start may have been reported, but not the magnitude of the engine overspeed.

During this quick start, an inlet valve may become stretched (Tuliped) and therefore slightly longer.

If the hydraulic tappet valve clearances have been set at the minimum value or the valve seat in the cylinder has worn, the stretched valve expands lengthwise (taking up all the available gap clearances) when the engine is running hotter at a high power setting and then does not quite seal on the cylinder head seat.

This then allows the cylinder to run very inefficiently and in a worse case, the combustion flame caused by the spark plug – through the slightly open inlet valve - starts combustion of inlet gases destined for other cylinders.

One of cases known to us had the pilot report a loud “banging” noise immediately preceding what he described as ”someone putting a brake on the engine”. Again as in previous cases, the engine did not stop running – it simply had no power.

The solution is to replace the tuliped inlet valve and ALL the hydraulic tappets. It seems that the tappets “look OK” when the mechanic checks them for damage and leak down, however the hammering during the engine overspeed must do something to also weaken their springs and they tend to fail, not doing the job of keeping a zero backlash in the valve train system. You can pick this by noisy (ticky) tappets when the engine is hot and sometimes a lack of “grunt” from the engine (the extra valve clearance means that the valve timing is out a little) and therefore changing the timing of the amount of fuel/air mixture that can enter the cylinder.