Spark plug gapping

[BigD]

I just purchased my first set of spark plugs since I purchased plane six years ago. Electrodes we’re oval shaped and I decided it was time. Where do I go for gapping number? Can’t recall. Thanks!

 

 

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[PT20J]

It’s in the Service Manual. Also, here is the Lycoming service instruction including torque specs.

SI1042AG Approved Spark Plugs.pdf

[EricJ]

There's a go-no-go gauge that's useful for determining when the electrode oval is too oval or not for massive plugs. 

https://www.aircraftspruce.com/catalog/topages/sparkplug12-03392.php

Also, this gap gauge is very common and useful for GA massive plugs:

https://www.aircraftspruce.com/catalog/topages/ATSgap.php

There are a number of tools used for setting the gap, so just check around if you don't yet have a decent one.    There are a few "spark plug tool kits" around that have some of this stuff bundled together, which is a good way to accumulate the tools if you're just starting.   Look at spruce or Aircraft Tool Supply or similar places online.

[MikeOH]

What @EricJ said.

 I bought a kit with a caddy, gapping tool, gauge, and anti-seize from Spruce. The caddy is really nice for rotating the plugs.

[Fly Boomer]

4 hours ago, BigD said:

 

I just purchased my first set of spark plugs since I purchased plane six years ago. Electrodes we’re oval shaped and I decided it was time. Where do I go for gapping number? Can’t recall. Thanks!

 

 

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The chart on PDF page 5 will get you started (see attached).

Champion Aerospace Catalog.pdf

[BigD]

Thanks y’all. I have all those tools -I was just looking for the number. I’ll check tomorrow I think it’s .16. I have it at hangar.


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[Hank]

7 hours ago, BigD said:

Thanks y’all. I have all those tools -I was just looking for the number. I’ll check tomorrow I think it’s .16. I have it at hangar.


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I recollect that the 0.016" gage must move freely, and the 0.019" won't go in. But I've not done it in a while.

[BigD]

I recollect that the 0.016" gage must move freely, and the 0.019" won't go in. But I've not done it in a while.

Thanks Hank!


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[M20F]

Massives are nice, you don’t feel as bad when you drop one on the floor and beak it.  
 

Finewires are better though, I won’t go back. 

[BigD]

All were ovals. I have replaced with new. I think the last time they were new was over 20 years ago and over 500 hours. I wish I had done it when I purchased plane in 2018. Plugs were cheaper then! 

[201Steve]

I keep a spare plug in my tool bag. Haven’t needed it yet but, how close to proper gap do the typically run when new? 

[N201MKTurbo]

32 minutes ago, 201Steve said:

I keep a spare plug in my tool bag. Haven’t needed it yet but, how close to proper gap do the typically run when new? 

You must keep that spare plug in your plane, it keeps all your plugs from fouling. As soon as you remove it from the box on the hat rack, you are guaranteed a fouled plug.

[cliffy]

I learned from a guy that worked on DC-3s and DC-6s (big round motors with  lots of plugs to change)

He always used just clean engine oil upon installation. Put a drop on his finger a rolled the threads trough it

He never had a seized plug.  I've done it that way for 55 years also and I've never had a seized plug on any engine.