Valve Clearance/Lash

[Auto Doc's]

It is kind of a weird situation. There is no direct sensor for the valve clearances but the valve clearances out of spec changes the readings on the MAP sensor that if you know what you are looking at can tell the valve clearances. It is not a direct read system, more a deviation that results from changes in valve clearances.

That is because the MAP is reading the running engine intake air vacuum. compared to the atmospheric pressure. When the valve clearances are not correct the MAP will sense this because the vacuum will be lower than what the sensor is calibrated to read as normal.

I've also worked as an auto mechanic for many years, and MAP sensors were very common on the first fuel injection vehicles.

 

[Auto Doc's]

MAP is all about pressure as in atmospheric. Not really anything to do with valve clearances.

I highly doubt, Briggs, has an OPTICAL sensor (high precision) on the cam or rocker arm/s that talks to the ECU like this. Maybe they do, I do NOT know.

Valve clearance and crank POSITION are different potatoes. Is Briggs looking at valve clearance to monitor crank position now? They better have solid steel cam gears and optical sensors. Why does that sound backwards? I'm willing to learn.........

MAP sensor - Wikipedia

en.wikipedia.org

 

[slomo]

I get the MAP part. There would be more dynamic loading with cutting grass or not, cloudy day vs full sun going up hill towing a core aerator. AGL above ground level where the person lives with said mower. Yes valve clearances effect dynamic cylinder compression, nothing huge but small. If the dynamic compression is now slightly lower with valves out of whack, I can see this working. MAP is reading the intake manifold pressure/vacuum.

So engine off, MAP knows the pressure. Engine on, new MAP reading, looks at say a fuel map or parameters for a proper running engine. Any deviance's possibly adjusts air/fuel ratio to run proper.

Think I'm making this harder than what it really is. I need a nap LOL.

 

[Auto Doc's]

I get the MAP part. There would be more dynamic loading with cutting grass or not, cloudy day vs full sun going up hill towing a core aerator. AGL above ground level where the person lives with said mower. Yes valve clearances effect dynamic cylinder compression, nothing huge but small. If the dynamic compression is now slightly lower with valves out of whack, I can see this working. MAP is reading the intake manifold pressure/vacuum.

So engine off, MAP knows the pressure. Engine on, new MAP reading, looks at say a fuel map or parameters for a proper running engine. Any deviance's possibly adjusts air/fuel ratio to run proper.

Think I'm making this harder than what it really is. I need a nap LOL.

You're getting the idea. The MAP constantly monitors all conditions as soon as key is turned on. The MAP reads the conditions and makes constant fine adjustments in milliseconds of time so the engine controller can adjust injector on time for more fuel as demanded.

 

[Skippydiesel]

The small planes I flew all we did was to adjust the mixture for best speed, no charts. Of course these never get above 10,000. And whenever we had engine problems we went to full rich setting and turn on the carb heater.

Best speed is not necessarily best economic speed.
A common method, to achieve best power setting is for aircraft fitted with pilot controllable carburettors, (air/fuel mixture) will usually have a recommended process for taking the engine to peak exhaust temperature and then either going lean or rich of peak.
Carby heat will reduce best engine power. Combining both full rich and carby heat could have a significant negative effect on engine performance, depending on altitude & climatic conditions.
Carby heat should only be applied when about to reduce engine power Or when in known/suspected icing conditions (eg descent into circuit) as a method of minimising carburettor ice