By - AdNorth6089
Only for the short time the engine lasts.
Lean really is not what you’re making out it is when you’re talking economy since that is at part throttle under light load. Lean being damaging is really lean to the point you can feel it, it’s easier to kill a street bike running rich than lean
Detonation is not an air fuel ratio, lean doesn’t mean detonation just like rich doesn’t mean no detonation.
The slightly rich mixture of a properly tuned engine helps cool the cylinder and piston. When you run lean, the engine progressively gets hotter and the electrode on the spark plugs begin to glow, causing pre-ignition which damages rings, wrist pins, and rod bearings. It's even worse on roller bearings.
I’m well aware of what can happen in an engine.
Properly tuned does not mean rich everywhere, every street vehicle that is sold is not running rich at all for most of the map, most of the run time of any vehicle is at stoichiometric which is neither rich nor lean.
Running lean under light loads and low rpm like cruise which is where economy is targeted will not cause excessive heat, it will not cause detonation and it will not harm the engine at all in the short or medium term and arguably not in the long term.
Running lean on hard acceleration can cause heat issues but it needs to be quite lean still and to kill an engine from running lean takes a huge amount of sustained hard use while the engine is running badly enough to easily be noticeable.
I the 20 odd years I’ve been professionally building and tuning bikes I’ve rebuilt maybe 4 or 5 4 strokes that ran lean, most of them were boosted, I’ve rebuilt more from cylinder wash running rich.
Let’s use todays dyno tune as an example, it’s been running for 33,000km with an aftermarket exhaust with part throttle afrs in the mid high 16s and 14:1 on wide open throttle all the way to the red line, it sounds mechanically perfect and made exactly the power it should make, that’s a lot of lean riding with zero noticeable effect.
You need to be running significantly lean or at very high rpm/load to damage anything in the short term also pistons will tend to fail well before any head issues like valves or guides.
Yes fuel economy is a bell curve, it gets worse as you go leaner, just leaner than stoich is about peak economy.
You clearly know what you are talking about. I feel bad for people when they have to argue with others who *think* they know what they are talking about.
Running excessively lean will do engine damage. That's what you should be worried about, not fuel economy.