Spark plug anti seize question.

[Daleandee]

The way to being always easy to remove plugs next time without damaging the helicoil, was to carefully wire brush the threads in the cylinders with a small rotating wire brush in a drill to remove the crud. Doesn't anyone else do this? Reinstall w anti seize of course.

Wouldn't that put the crud in the cylinder? The reason we use a blow gun around the plugs before removal is to help prevent stuff from falling inside ...

 

[Dan Thomas]

Wouldn't that put the crud in the cylinder? The reason we use a blow gun around the plugs before removal is to help prevent stuff from falling inside ...

That's why I prefer the black stuff from Champion or whoever. It doesn't have the metals and minerals that accumulate in those threads and gum them up. It goes on really thin, as you only need a thin film to prevent eventual seizure. The fit of those threads is pretty close and doesn't need thick, heavy goop.

Look again at those excerpts from the TCDSs I posted. Aluminum, zinc, copper, and nickel powders; calcium oxide, magnesium silicate, limestone, amorphous silica. Lots of crud that accumulates in there. I would expect the calcium, limestone, silica and silicates to be abrasive, too, and you don't want that falling into the cylinder.

 

[Domenick]

I've been using the "heavy goop" for twenty years and never needed to clean the cylinder threads on my O-320-D3G. That engine (since replaced) went 2925 hours.

 

[nrpetersen]

The other part of plug removal ritual is to first remove the bottom plug, then only remove the top plug when the piston is at TDCenter when both valves are closed. Seems to me that the potential contamination crud around the piston top ring groove could be an order of magnitude more than might be dropped inside from from plug removal. To me seizure and helicoil damage would a big deal, and never approached.

 

[3393RP]

You speak truth! After twenty years I'm still taking little dabs out of the cap ...

I've had these two tubes for more than 20 years. One was at my shop in a small town 15 miles away from home, the other in the garage. In 2022, we built a house on the property where the shop is located, and moved from the big city to the country.

I don't use much since I quit racing in 2007, but there's still wheel studs and other things that need a dab. At the current rate of consumption, I'll still have plenty to use on my casket hinges.

 

[texasclouds]

 

[Clip4]

I just use aviation motor oil on the threads. They never seize.

 

[Dan Thomas]

The peak voltage in the primary winding is much higher than 14V because of the "inductive spike" generated when the points open (or the transistor turns off). 100-200V typically. Same deal with magnetos.

That is NOT how you measure the turns ratio in a transformer. A common method is to apply a known AC voltage to one winding and measure the open circuit voltage of the other winding(s). Your DC resistance method is woefully inaccurate because the secondary of an ignition coil is wound with much finer wire than the primary and so has much higher resistance per turn. The finer wire is used because a) it takes up less space and b) the lower current in the secondary allows this without overheating.

Here is a scholarly article on magneto theory:

https://ntrs.nasa.gov/api/citations/19930091186/downloads/19930091186.pdf
P. 11 lists a turns ratio of 57:1. P.15 lists an average spark current of .033A (33mA). Both of these numbers reasonably close to my example.

I had to do a little digging; there are very few magneto manuals that mention the number of turns of primary and secondary turns in the aircraft magneto's coil. From this article https://aerotoolbox.com/magneto/ I see these excerpts:

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So, your earlier assertion of about 100:1 is correct. The sudden fall of the flux is responsible for generating the secondary's high voltage, as opposed to the gradual fall of an AC sine wave as with a normal transformer. Shoot, I knew that, having taught it in Aircraft Systems in college, and I knew about voltage spikes as presented by the master contactor when it is shut off (also generated by the starter and its contactor), spikes that are famous for frying sensitive electronics that might be turned on at the time. I once used my oscilloscope to determine that the master's spike was around 600 volts, much of which is absorbed by the battery, and in many airplanes, shunted by a diode across the coil. But we still lost too many encoders that were connected directly to the radio breaker in non-avionics-bus airplanes, and they would get some spikes, probably more off the starter than the master contactor.