respectable

[WEST OZ FLYER]

Tony, think of the vacuum advance as a ignition timing retarding device under load. When you go around a corner in a gear higher than you should be, high engine load, the timing will retard as you have very little vaccum because the throttle is pressed heavily, ie throttle butterfies open. This will bring your timing back to the base setting governed by your engine rpm. There is also a mechanical fly weight system in your distributor that advances your timing as to your engine rpm increases. As your engine spins faster the spark still travel the same speed along the ignition leads so advancing the timing is neccessary to achieve optimum timing for your engine. This can be changed by spring and/or flyweight mass changes depending on the engines needs. This is call re-graphing or re-curving of the distributor.

Now when the engine comes back under light load, idle or coasting, throttle butterflies closed or slightly open, the timing will advance because you now have a vacuum reading hence vacuum advance. This is there for fuel economy, emissions and idle quality in motor vehicles. You will notice that your Subaru manual will state timing adjustments are to be done with vacuum advance disconnected and blocked off. Next time you have access to a EA81 with vacuum advance working check the timing at idle and then check with it disconnected and blocked off.

Moving on to aircraft use. Your engine will only be at 100% load where you pitch you prop at for maximum rpm. As aircraft can't coast or be at a high engine load at low rpm you don't need vacuum advance.

Hope that makes sense.

[WEST OZ FLYER]

With the compression test for diagnosis I do them cold and record the reading. Do them hot and record the reading.

If they are the same hot and cold it could be rings, valves or head gasket. Think wear or tolerances.

If the pressures go down when hot it could be rings or piston to bore clearances, cracked head etc. Think expansion.

Then put a good squirt of oil in the cylinders and do it again. If the pressures come back up it is rings if not it is valves, head gasket etc.

Sorry it has been a big day at work. I hope this all makes sense.

A leakdown test is by far the best.

[mad max]

The most reliable EA81 I had which was trouble free for 10 yrs or so and is still running at Byron Bay at one time had one compression down 10 lbs. but as the engine ran good I ignored it and re-checked a yr. later and the compressions were even. I can't remember the numbers but think they were all under 150lbs. However my compresion gauge is almost as old as me. I recently checked my EJ25 which is running perfectly and they all read 130 according to the gauge

[mad max]

Hi Tony. I've never hooked up the vacuum to the Dist. The best EA81 I ever had and is still flying at Byron Bay had a modified engine cam and no advance weights in the dist. The GA mags. I used to overhaul in the 70's had no advance mechanism

[tonydenton]

hello MATTHEW, I can understand all that when I read it but will never be able to remember it . but now I have been told. ha ha. so thank you. I just needed another opinion worried why it was set up a certain way. some things on the engine were never right from the all those years ago. thanks heaps

[tonydenton]

thank you too max. that is a good run hope I'm that lucky.

[Tim]

[Tim]

Oops, I was stuck on page one and didn't realise there were more good answers following.

[WEST OZ FLYER]

Tim, it has been my observation that early distributors (pre unleaded) have way more mechanical advance than the later ones. Point distributors were by far the worse.

Tony the most important thing with timing in your gyro is maximum advance. I would run mine at 28* BTDC. Anything after that made no power difference. So as long as you can wind the engine over on the starter without it pushing pistons down it will be fine. Most EA81 distributors have around 15-20* mechanical advance so your static timing should be 8-12*. You will not hear detonation in your gyro over the propeller. Tread carefully.

Have a read of this. http://4secondsflat.com/Spark_plug_reading.html

Sparkplugs can tell you way more about your engine than you think. And the there is the vacuum gauge.

[RossM]

That guy knows his spark plugs.
I know stuff all about motors, but do agree with him, you can tell from the forth picture of a spark plug that the rear tyre does need a bit more air in it.

[WEST OZ FLYER]

Yeah Ross, he knows his stuff. That is not the page I was looking for but from that guy. I sent it to Chook last year. I will see if he still has the link.

Chook are you reading this?

[chook]

Yes Matt and I have had a look back and can't locate either your email or my notes on it which is a bit perplexing.
From memory NGK gave a reasonable explanation of the subject as well.

Regards........Chook.

[RossM]

https://www.ngksparkplugs.com/about-ngk/faqs/spark-plug-faqs

Use safety glasses and gloves before starting maintenance

When should I use a resistor spark plug?

A: NGK "R" or resistor spark plugs use a 5k ohm ceramic resistor in the spark plug to suppress ignition noise generated during sparking.

NGK strongly recommends using resistor spark plugs in any vehicle that uses on-board computer systems to monitor or control engine performance. This is because resistor spark plugs reduce electromagnetic interference with on-board electronics.

They are also recommended on any vehicle that has other on-board electronic systems such as engine-management computers, two-way radios, GPS systems, depth finders or whenever recommended by the manufacturer.

In fact, using a non-resistor plug in certain applications can actually cause the engine to suffer undesirable side effects such as an erratic idle, high-rpm misfire, engine run-on, power drop off at certain rpm levels and abnormal combustion. What is a fouled spark plug?

A: A spark plug is considered fouled when the insulator nose at the firing tip becomes coated with a foreign substance such as fuel, oil or carbon. This coating makes it easier for the voltage to follow along the insulator nose, leach back down into the metal shell and ground out rather than bridging the gap and firing normally.

Many factors can contribute to spark plug fouling. The air-fuel ratio may be too rich as a result of incorrect carburetor adjustment or a poorly performing fuel injection system. Worn piston rings or valve seals may allow too much oil to leak into the combustion chamber, leading to oil fouling. The ignition system may not be performing properly. Prolonged idling or continuous low-speed driving may keep the spark plug from reaching its optimum operating temperature. Using too cold a spark plug can lead to the same problem. Finally, a dirty air cleaner can create a too-rich condition which can lead to fouling.

Fuel, oil and carbon fouling can all be the result of different causes but, once a spark plug is fouled, it will not provide adequate voltage to the firing tip and that cylinder will not fire properly. Therefore, it is recommended that a plug be replaced once it is fouled. How do I read a spark plug?

Normal Condition
An engine's condition can be judged by the appearance of the spark plug's firing end. If the firing end of a spark plug is brown or light gray, the condition can be judged to be good and the spark plug

is functioning optimally.







Dry and Wet Fouling
Although there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. If the insulation resistance drops to 0 ohms, the firing end is fouled by either wet or dry carbon.





















Overheating
When a spark plug overheats, deposits that have accumulated on the insulator tip melt and give the insulator tip a glazed or glossy appearance.


How do I install spark plugs correctly?

A: It is essential to tighten a spark plug to the specified turning angle or torque setting. First, screw in the plug finger tight until the gasket meets the cylinder head. Then seat the plug/gasket with a torque or turning angle wrench as specified in the chart below.

Spark plug type	Thread Diameter	Cast Iron Cylinder Head (lb-ft.)	Aluminum Cylinder Head (lb-ft.)
Flat seat type (with gasket)		25.3~32.5	25.3~32.5
		18.0~25.3	18.0~21.6
		10.8~18.0	10.8~14.5
		7.2~10.8	7.2~8.7
		--	5.8~7.2
Conical seat type (without gasket)		14.5~21.6	14.5~21.6
Conical seat type (without gasket)		10.8~18.0	7.2~14.5

This is very important, as excessive tightening of a spark plug can cause breakage of the metal shell and damage to the interior seals. At the same time, insufficient tightening can lead to overheating of the spark plug and potential detonation.





Anti-seizeCorona stain

Corona stain is observed as a light brown or tan discoloration above the hex (located on the ceramic body of the spark plug). Corona stain is created by oil or dirt particles surrounding the spark plug. Spark plugs create a high amount of static electricity as they fire, attracting these particles to the exposed ceramic between the plug boot and the hex. Corona stain is completely normal and should not be mistaken for exhaust gas blow-by or broken seals inside the spark plug.

Gapping spark plugsTorque Understanding Heat Range

• Step 1: Disconnect the spark plug lead. Number the leads so that the correct leads are connected after the plugs have been installed.
• Then, clean the area around the spark plug to avoid getting debris in the combustion chamber when you remove the plug.
• Step 2: Remove the spark plug using a spark plug socket.
• Step 3: Clean light deposits from the plug with a soft brush and solvent. Never use petrol.
• (Petrol contains methane and benzene, which are dangerous hydrocarbons. Think of using appropriate PPE, such as gloves and barrier cream , before handling petrol).
  
  You can also use a sturdy tool to scrape off tough deposits, cleaning down inside around the insulator. Make a fine point tool from a hacksaw blade. Do not damage the insulation.
• Step 4: Inspect the spark plug for very stubborn deposits, or for cracked porcelain or electrodes that have been burned away. If any of these conditions exists, replace the spark plug.
• Clean the electrode and earth with a spark plug file. The surfaces should be clean, flat (not rounded) and square to each other
• Step 5: Check the spark plug gap and adjust as necessary.
• Step 6: If it seems in working order, replace the plug, taking care not to over-tighten (see engine manufacturer recommendations) and re-attach the spark plug lead.
• Note: NEVER clean a spark plug with a shot blaster or abrasives.

[RossM]

cripes, did I post that. it is no longer on their website

[WEST OZ FLYER]

Yep you did post that.

[RossM]

but did you read it Matthew?

[WEST OZ FLYER]

Yes mate, was there anything specific you were refering to?

[RossM]

no, just seemed a lot to read